WO2001067094A2 - Device and method for bringing a compound into contact with an environment - Google Patents
Device and method for bringing a compound into contact with an environment Download PDFInfo
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- WO2001067094A2 WO2001067094A2 PCT/IB2001/000307 IB0100307W WO0167094A2 WO 2001067094 A2 WO2001067094 A2 WO 2001067094A2 IB 0100307 W IB0100307 W IB 0100307W WO 0167094 A2 WO0167094 A2 WO 0167094A2
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/18—Water
- G01N33/1826—Organic contamination in water
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/24—Earth materials
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/20—Controlling water pollution; Waste water treatment
Definitions
- the present invention pertains to a device and a method for releasing a compound, preferably a pesticide, into a predetermined environment, preferably a subsurface reservoir.
- the device and the method is useful for monitoring the degradation or sorption of the released substance in the environment.
- the invention will be useful for generating data on the degradation or sorption of e.g. pesticides in an environment. The data can be evaluated by regulatory authorities prior to decisions concerned with e.g. issuance of marketing authorisations.
- Pesticides are a generic term comprising a large number of completely different compounds used for the control of weeds, harmful insects etc. Pesticides are divided into different groups, determined by the target. The most common of these groups are herbicides against weeds, insecticides against insects, and fungicides against fungi.
- Pesticides such as chlorinated hydrocarbons, organophosphorus pesticides, phe- noxy acids, triazines, thiocarbamates and captan have all been developed and used during the past decades in an attempt to control weeds, insects and fungi. Even though many of the pesticides have been banned for a number of years, some of them are now being detected in groundwater. This is causing a problem as the access to groundwater reservoirs for drinking water purposes is restricted. Also, the groundwater may require extensive purification.
- Pesticides are continually being developed by the agrochemical industry, and a new generation of pesticides such as synthetic pyrethroides, sulfonylureas and benzim- idazoles have been developed in recent years.
- the toxicological and environmental behaviour of such pesticides has to be tested, before they can be registered. These tests are routinely performed by the agrochemical industry. Proper and accurate testing methods are required in order to document the environmental effects of using the pesticides.
- Pesticide contamination of surface- and groundwater may be caused by improper handling of the pesticides or result from normal agricultural practices. Pesticides are not only toxic to the target organisms, and it has been established that in some cases only about 1 % of the total amount of pesticide is effectively utilized (Dahi et al. (1989): Laarebog i Vandforurening med Milj ⁇ gifte (in Danish), Technical Univer- sity of Denmark).
- the environmental effect of the use of pesticides depends largely on the annually applied quantity, the concentration, the toxic effect of the pesticide, and the resistance towards degradation in soils and water (Beitz et al., 1994, (Ed.: H. B ⁇ rner): Occurrence, toxicological and ecotoxicological significance of pesticides in Ground and Surface Water, p. 3-56).
- the toxic effect of pesticides can be evaluated from tests, in which predetermined organisms are influenced by different doses during a certain period of time (normally from 72 to 96 hours).
- the toxicity can be measured from one or more of the following:
- LD 50 The dose (e.g. oral dose), which results in 50% mortality among the test organisms.
- EC 50 The concentration, which results in 50% inhibitance of e.g. algae production.
- NOEC Maximum concentration, which results in no visible effect on the test organisms.
- Pesticide degradation processes may be abiotic or biotic. Considering pesticide degradation processes in general, non-redox reactions are typically abiotic (McNab & Narasimhan (1994): Degradation of Chlorinated Hydrocarbons and Groundwater Geochemistry: A Field Study. Environ. Sci Technol., 28, p. 769-775). Both abiotic and biotic degradation processes can be influenced by soil parameters such as particle distribution, mineral composition, organic matter content, humidity, pH, temperature and redox potential. In addition, biotic processes are affected by the bio- mass, the composition of the microbial population, and the availability of nutrients. Microbial degradation of pesticides occurs much more frequently than abiotic degradation. As abiotic degradation products are much the same as those of enzymati- cally catalysed processes, it may be difficult to distinguish between abiotic and biologic degradation.
- Biotic processes include processes in living organisms or processes catalysed by enzymes inside or outside living cells. Microbial degradation of a large number of pesticides have been demonstrated, and several pesticide degrading microorganisms have been isolated. Microorganisms capable of metabolising pesticides gain energy thereby, and the pesticides are degraded and, normally, to some degree mineralised into low molecular weight inorganic products like CO 2 , H 2 0 and CI " .
- the biodegradability of pesticides is normally characterized by their half lives. However, this presupposes that the degradation follows first-order kinetics, and this in turn presupposes that the degradation rate is proportional to the concentration of residual pesticide.
- a pseudo first-order degradation requires a very low pesticide concentration (which is usually found in groundwater), or a high pesticide degrading potential. At low substrate concentration, diffusion may be the limiting factor for the substrate available to the microorganisms. Also the rate constant depends on the biomass, and the pesticide must be the sole carbon source for the degrading organisms.
- Humidity is possibly the most important factor next to the number of microorganisms. This is due to a higher bioreactivity in humid environments because sub- strates and nutrients are transported much more readily in such environments.
- the present invention makes it possible to follow the transport and/or the degradation and/or the sorption of e.g. a pesticide in a groundwater reservoir.
- the invention provides a simple way for determining if a pesticide is either bound to a sediment (sorption), if a pesticide is maintained in a groundwater reservoir, or if a pesticide is degraded, and in the latter case, if the degradation is caused at least partly by mi- croorganisms.
- Such a determination of the possible outcome of using pesticides is essential for evaluating whether or not the pesticide in question should be granted a marketing authorisation. Accordingly, the present invention represents an important commercial value, as there do not exist for the present time a sufficiently reliable method that is capable of evaluating for example the degradation and transport of pesticides in a groundwater reservoir.
- US 5,605,634 Mackay & Wilson; University of Waterloo describes a method for discharging a substance to the groundwater.
- a low density polyethylene (LDPE) tubing can be used.
- the tubing has a thickness of 0.33 mm. This thickness only allows passage of solutions consisting of small, low polarity molecules in sufficient amounts.
- a pump in the dis- closed method, and, following introduction of a substance from a surface reservoir, the solution containing that substance is circulated in the LDPE tube and returned to a reservoir.
- One method is based on pumping a substance, for example a pesticide, and a tracer into a groundwater reservoir.
- the degradation and/or flow of the substance and/or the tracer can then be followed by state of the art monitoring techniques.
- This method has several drawbacks.
- First of all it is difficult during prolonged periods of time to discharge - by means of pumping - a constant amount of a substance and tracer into the reservoir, since a pump will not be running sufficiently evenly over long periods of time, and since a problem with the pump inevitably gives rise to a major problem with both discharging the substance and handling of the generated data.
- the system is dependent on electricity - a resource often not available at remote locations - and ordinary maintenance, and thirdly, the pumping cannot avoid disturbing the natural flow conditions on the locality in question.
- Another method requires isolation of a sediment from a groundwater reservoir and transfer of the sediment from the reservoir to closed laboratory incubations. It is important, but quite impossible under practical conditions, that the conditions in the laboratory and in the groundwater reservoir are identical. In the laboratory the sediment is supplemented with an aqueous solution of a pesticide, and degradation or sorption of the pesticide over time is monitored. It is clear that this method is a closed, static system while an aquifer is a dynamic system due to the natural groundwater flow with the possibility of exchange of e.g. essential nutrients with the surroundings. Also, in laboratory incubations the groundwater chemical conditions may be changed quite radically during the time in which the experiments take place.
- the oxidative/reductive properties of the sediment may change during sample isolation, storage and analysis in the laboratory. It is difficult for an anaerobic sediment sample not to be contaminated by oxygen during isolation, storage or analysis. Also, transfer of the sediment cannot avoid affecting the microorganisms that are present in the sediment, and the microorganisms may for example be subjected to alterations affecting their growth and contact with nutrients, light, temperature and redoxpotential.
- the flow direction is not necessarily the same as under the natural conditions, the total volume of a sediment capable of being investigated in this way is very limited, and the method cannot be expected to be representative for the conditions characterising the natu- ral groundwater reservoirs on the locality from where the sediment was isolated.
- Another major weakness of this method is that it is very complicated to carry out such experiments under anaerobic conditions. This is all the more critical for sediments isolated from anaerobic environments.
- the present invention concerns a device for passively releasing a substance to an environment and a method for determining the degradation and/or sorption of the substance in question in the environment.
- the invention is useful for analysing the degradation and/or sorption of organic compounds in an environment such as a natural groundwater reservoir.
- the invention is particularly useful for analysing organic compounds including pesticides that are moderately polar and preferably less polar than water.
- the device according to the inven- tion does not require any maintenance, or only a minimal maintenance, and it is simple and economical to install in any given locality of interest.
- the invention makes it possible to determine - without any further experiments or analysis - the degree to which a given pesticide might be adsorbed/absorbed to a sediment or, alternatively, degraded, and in the latter case, if such degradation takes place by purely abiotic means or if it is being catalysed by microorganisms.
- the present invention solves the problems associated with the prior art methods listed herein above.
- an emitter cell comprising
- a compartment comprising a fluid composition comprising at least one of a) an assayable compound, and b) a tracer moiety, or a combination of both,
- composition comprised in said compartment is separated from a predetermined environment by at least one selectively permeable membrane capable of bringing at least one of said a) and b), when present, or a combination of both, into contact with said predetermined environment, and
- the present invention pertains to an emitter cell comprising
- a compartment comprising a fluid composition comprising at least one of a) an assayable compound, and b) a tracer moiety, or a combination of both, ii) wherein said composition comprised in said compartment is separated from a predetermined environment by at least one selectively permeable membrane capable of bringing at least one of said a) and b), when present, or a combination of both, into contact with said predetermined environment by means of passive diffusion.
- Yet another aspect of the invention relates to a device comprising a plurality of operably linked emitter cells according to the invention.
- a further aspect of the invention pertains to a kit comprising the emitter cell according to the invention and/or the device according to the invention in combination with detection means for detecting one or more of said assayable compound and said operably linked detectable substance and said tracer moiety and said further tracer moiety.
- the present invention relates to a method for monitoring at least one assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of:
- a further aspect of the present invention pertains to a method for monitoring at least one assayable compound and/or an operably linked detectable substance in a predetermined compartment, said method comprising the steps of:
- a method for monitoring the sorption of an assayable compound and/or an operably linked detectable substance in a predetermined environment comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the sorption of said assayable compound and/or said operably linked detectable substance in said predetermined environment.
- a method for monitoring the biotic degradation of an assayable compound and/or an operably linked detectable substance in a predetermined environment comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the biotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined environment.
- a method for monitoring the biotic degradation of an assayable compound and/or an operably linked detectable substance in a predetermined environment comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the biotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined compartment.
- a still further aspect of the invention pertains to a method for monitoring the abiotic degradation of an assayable compound and/or an operably linked detectable sub- stance in a predetermined environment, said method comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the abiotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined environment.
- a further aspect relates to a method for monitoring the abiotic degradation of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the abiotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined compartment.
- a method for monitoring the stability of an assayable compound and/or an operably linked detectable substance in a predetermined environment comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the stability of said assayable compound and/or an operably linked detectable substance in said predetermined environment.
- Yet another aspect pertains to a method for monitoring the stability of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the stability of said assayable compound and/or an operably linked detectable substance in said predetermined compartment.
- the present invention relates to a method for monitoring at least one tracer moiety in a predetermined environment, said method comprising the steps of:
- a method for determining the flow of at least one tracer moiety in a predetermined environment comprising the steps of the method for monitoring at least one tracer moiety, and at least a further step of monitoring the flow of said tracer moiety in said predetermined environment.
- a method for monitoring at least one assayable compound and/or an operably linked detectable substance in a predetermined compartment comprising the steps of:
- Compartment Section of emitter cell comprising a composition of matter sur- rounded by a membrane defining a division between said composition comprised in said compartment and an external environment.
- Open compartment Compartment in operably contact with an external source capable of providing said compartment with additional composition of matter and op- tionally maintaining a steady state concentration of said matter comprised in said composition.
- Assayable compound Compound capable of being determined or detected either quantitatively or qualitatively by means of any assay suitable for such detection.
- Tracer moiety Moiety retaining identical or substantially identical means for identification at least during assaying or detection.
- Predetermined environment Any environment wherein an assayable compound or a tracer moiety is capable of being released under practical circumstances.
- Selectively permeable membrane Membrane that is permeable for a given substance, and impermeable for other substances. Permeability may be defined on the basis of chemical and/or physical properties of a given substance.
- Passive diffusion Bringing a composition of matter comprised in a closed compart- ment into contact with a composition of matter comprised in a predetermined environment.
- Semi-passive diffusion Bringing a composition of matter comprised in a open compartment into contact with a composition of matter comprised in a predetermined environment.
- Detectable label Substance capable of revealing quantitative or qualitative properties of a moiety or a compound.
- Reversibly bound compound or moiety Compound or moiety capable of existing in a bound as well as an unbound form.
- Polymer is understood within the ordinary meaning at this term and comprises molecules formed by the union of at least one type of monomer.
- the compartment according to the invention may comprise a fluid composition comprising either a) an assayable compound, or b) a tracer moiety, or a combination of both a) and b).
- the fluid composition comprising said compound and/or said tracer preferably comprises a liquid composition such as e.g. an aqueous solvent.
- an emitter cell wherein a) is brought into contact with said environment by means of passive diffusion in the absence of b).
- the present invention pertains to an emitter cell wherein a) is brought into contact with said environment by means of passive diffu- sion and b) is brought into contact with said environment by means of semi-passive diffusion.
- an emitter cell wherein a) is brought into contact with said environment by means of semi-passive diffusion and b) is brought into contact with said environment by means of passive diffusion.
- the invention relates to an emitter cell wherein both a) and b) are brought into contact with said environment by means of passive diffusion.
- both of the assayable compound a) and the tracer moiety b) is brought into contact with said environment by means of passive diffusion.
- the present invention overcomes the problems associated with prior art solutions to a similar problem.
- the present invention renders the use of a pumping source superfluous, and the expenses associated with acquiring and running a pump can be saved. This also eliminates any problems associated with periodically uneven pumping speeds as well as any problems arising when the natural flow on the location is being disturbed by the pumping source.
- an emitter cell wherein b) is brought into contact with said environment by means of either passive diffusion or semi-passive diffusion in the absence of a). It may be advantageous to initially bring the tracer moiety b) into contact with said external environment in order to deter- mine the flow of groundwater on the location in question. When the flow direction has been determined it is possible to carry out an experiment wherein the assay- able compound a) and optionally also the tracer moiety b) is brought into contact with said external environment.
- the advantage associated with such a two-step method is that no assayable compound is released in vain, if the direction of the flow of groundwater should be different from that expected.
- Passive diffusion results in bringing the composition comprising the assayable com- pound and/or the tracer moiety into contact with an external environment.
- Passive diffusion as used herein is normally caused by a concentration gradient, that is different concentrations of said assayable compound and/or said tracer in different locations such as e.g. a compartment and an external environment separated by a boundary such as a membrane comprising a polymer allowing the diffusion to oc- cur.
- a passive diffusion may also be caused by a temperature gradient or a pressure gradient.
- the contact is established when the composition comprised in the closed compartment diffuses into the external environment.
- the contacting of the external environment and the composition comprising the assayable compound and/or the tracer moiety occurs in the compartment itself. This is the case when composition of matter from the external environment enters the compartment. However, contacting may also take place in both the compartment and the external environment.
- the emitter cell may also comprise a composition comprising at least one further assayable compound or a detectable substance operably linked to at least one of said assayable compound and said further assayable compound.
- the detectable substance is operably linked as used herein when said assayable compound and/or said further assayable compound is capable of being converted into said detectable substance. The conversion may take place by means of any form of chemical modification, or reaction with a chemical or biological agent including a microorganism.
- the operable linkage makes it possible to detect said assayable compound and/or said further assayable compound by means of detecting instead said detectable substance.
- the assayable compound and/or the further assayable compound is preferably selected independently from the group consisting of chemical compounds and the group consisting of biological compounds.
- Chemical compounds shall be understood to comprise any compound made by in vitro synthesis, whereas biological compounds relate to entities such as cells and viruses as well as their metabolites.
- Preferred biological compounds are microbial cells selected from the group consisting of eukaryotic microbial cells and prokaryotic microbial cells.
- earth bacteria such as Pseudomonas species are preferred, in particular Pseudomonas species such as e.g. Pseudomonas fluorescens.
- Preferred chemical compounds are pesticides including herbicides, insecticides and fungicides.
- One group of preferred pesticides comprise chlorinated hydrocarbons, organophosphorus pesticides, phenoxy acids, triazines, thiocarbamates and ni- troaromatics.
- Another group of preferred pesticides comprise synthetic pyrethroides, sulfonylureas and benzimidazoles.
- any pesticide including any herbicide, insecticide or fungicide, including any synthetic pyrethroide, sulfonylurea or benzimidazole, and any derivative thereof, suspected of being able to resist degradation in a soil sediment, or suspected of being able to remain in a soil sediment in concentrations or levels above those determined by the authorities as maximum recommendable values.
- any pesticide including any herbicide, insecticide or fungicide, including any synthetic pyrethroide, sulfonylurea or benzimidazole, and any derivative thereof, suspected of being able to resist degradation in a soil sediment, or suspected of being able to remain in a soil sediment in concentrations or levels above those determined by the authorities as maximum recommendable values.
- non-degradable or “slowly" degraded compounds are likely to enter groundwater reservoirs and render said reservoirs unsuitable for use in ordinary tap water, unless thoroughly cleaned or filtered.
- the assayable compound and/or said further assayable compound when present in water, preferably represents a potential health hazard for human beings, or a compound generally recognised as being undesirable for human and/or animal con- sumption.
- Such compounds are typically characterised by the authorities according to a LC 50 value, indicating the concentration, which results in 50% mortality among the test organisms, a LD 50 value indicating the dose (e.g. oral dose), which results in 50% mortality among the test organisms, or the EC 50 value providing the concentration, which results in 50% inhibitance of e.g. algae production.
- the tracer moiety according to the invention preferably comprises a detectable label. The label must be sensitive enough to facilitate detection or quantification of said tracer during use under practical circumstances.
- the de- tectable label preferably comprises a radiolabel and/or a fluorescently detectable label.
- tracer moiety comprises a radiolabel
- tracer in the form of tritiated water or tracer comprising tritiated water is preferred. This preference is due to the fact that the behaviour of tritiated water would be identical to or resembles the nature of an aqueous solution comprised in the compartment according to the inven- tion.
- preferred tracers are 3 H HO, 3 H 2 0, 2 H 2 0, 2 H 1 HO, 3 H HO, and
- Another tracer capable of being used in combination with the present invention is sulphurhexafluoride, SF e .
- One or more of said assayable compound and said further assayable compound and said tracer moiety may be reversibly bound to a solid phase.
- Reversibly bound shall be understood to comprise any association formed between said solid phase and one or more of said assayable compounds and tracer moiety that does not prevent said compounds or tracer from disassociating or reassociating themselves with said phase by any means of disassociation or reassociation.
- the solid phase pref- erably comprises a silica gel or a resin, more preferably a silica gel, and preferably only the tracer moiety is reversibly bound to said silica gel forming said solid phase.
- the emitter cell according to the invention may comprise a fluid or liquid composition comprising a plurality of different assayable compounds.
- the com- position may comprise for example from two to ten different assayable compounds, such as from three to eight different assayable compounds, for example from four to six different assayable compounds.
- composition may also comprise at least one further tracer moiety, such as from two to five different tracer moieties, for example three or four different tracer moieties.
- the emitter cell comprises a selectively permeable membrane comprising a polymer.
- Preferred polymers according to the invention are natural or synthetic poly- mers, such as e.g. polymers comprising nylon and polymers comprising polyethylene.
- the polymer preferably comprises a compound acting as co-polymer or block co-polymer. Said co-polymer or block co-polymer preferably has the effect of acting as a softening agent at least when comprised in the polymer.
- Polyethylene comprising ethylene methacrylate (EMA) as a random co-polymer is particularly preferred.
- the polyethylene is preferably a low-density polyethylene (LDPE), and the random co-polymer, preferably methacrylate, is preferably present in an amount of from 1 to 25 percent, such as from 12 to 24 percent, for example from 14 to 22 percent, such as from 15 to 21 percent, for example from 16 to 20 percent, such as from 17 to 19 percent, for example about 18 percent.
- preferred polymers comprise or at least essentially consist of ethylene vinyl acetate (EVA) or ethylene acrylic acid (EAA).
- the selectively permeable membrane comprising a polymer preferably has a thickness of less than about 2.0 millimeter (mm), such as less than about 1.0 mm for example less than 0.8 mm, such as less than about 0.6 mm, for example less than about 0.4 mm, for example less than 0.3 mm, such as less than about 0.2 mm, such as less than about 0.1 mm, for example about 0,075 mm, for example less than about 0.05 mm.
- a membrane comprising low-density polyethylene comprising ethylene methacrylate as a random co-polymer is preferably used with a thickness of less than 0.5 mm, such as less than 0.1 mm, for example about 0.075 mm.
- the polymer is substantially impermeable to charged particles including ionic species. However, it may also be preferred under some circumstances that the polymer is substantially impermeable to low polarity particles and particles that do not comprise any ionic charges. Additionally preferred polymers are polyvinyl alcohol, cellulose acetate, polydimethylsiloxane, polybutadiene, ethyl cellulose, and polymethyl methacrylate. Among these, polyvinyl alcohol, cellulose acetate, polydimethylsiloxane are more preferred because of their diffusive properties.
- the polymer may be any polymer that is functionally equivalent to low-density polyethylene (LDPE) comprising a co-polymer, for example a random co-polymer, pref- erably ethylene methacrylate, in an amount of 18 percent.
- LDPE low-density polyethylene
- the concentration of the compound or tracer in the fluid or liquid composition comprised in the compartment is substantially unchanged over time. This is preferably achieved for a closed compartment by including into said closed compartment a solid source comprising said compound and/or said tracer.
- a solid source of compound and/or tracer serves the purpose of supplementing the fluid or liquid source of said compound or said tracer comprised in said closed compartment with additional compound and/or tracer.
- This supplement in the form of the addition to the closed compartment of compound and/or tracer - per time unit - is preferably at least substantially equal to the amount of compound and/or tracer being released - per time unit - into a predetermined exter- nal environment from said closed compartment. In this way, the concentration of said compound or tracer in said fluid or liquid composition is kept at least substantially constant over at least part of the time of releasing said compound and/or said tracer into said environment.
- any changes in the concentration of said compound or tracer comprised in a fluid or liquid composition occur during the period of time wherein said compound and/or tracer is released into said environment, it is preferred that these changes are compensated for by an adaptation of the composition of said permeable membrane comprising a polymer according to the invention, wherein the term adaptation is understood to mean any change in the composition of said membrane or polymer capable of maintaining a constant flux of said compound and/or tracer irrespective of any change in their concentration when they are present in a liquid or fluid composition comprised in said compartment.
- such adaptations of the composition of the permeable membrane according to the invention preferably occurs by carefully selecting corresponding pairs of at least one polymer and at least one co-polymer, or corresponding pairs of at least one polymer and at least one block co-polymer.
- Adaptation as used herein may involve that the polymer in question becomes more permeable to the compound and/or the tracer over time.
- the increased permeability preferably counteracts any decrease in the amount and/or concentration of dissolved compound and/or tracer comprised in the compartment.
- either the membrane comprising the polymer ac- cording to the invention does not undergo any significant modifications causing the flux through the membrane of compound and/or tracer to be altered significantly over at least part of the period of time of releasing said compound and/or tracer, or alternatively, it is preferred that the membrane comprising the polymer according to the invention undergoes an adaptation as defined herein above capable of main- taining an essentially constant flux through the membrane of compound and/or tracer over at least part of the period of time of releasing said compound and/or tracer.
- the term "at least part of the period of time of releasing said compound and/or tracer” will be understood to exclude any initial period substantially shorter than the total release period, wherein “steady-state” release conditions are being established during said "initial” period.
- the "initial” period is often referred to as the "transient” period in the art.
- the length of said initial period preferably amounts to less than 10 percent, for example less than 5 percent, such as less than 2 percent, for example less than 1 percent, such as less than 0.5 percent of the length of the total release period being equal to the period wherein compound and/or tracer is being released or brought into contact with said predetermined external environment. It is much preferred that the emitter cell is capable of releasing essentially the same amount of assayable compound and/or tracer moiety per time unit under practical circumstances. This uniform release rate will simulate a "steady-state" release system and thus improve data quality and validity.
- the emitter cell pertaining to the present invention comprises a permeable membrane and optionally a further permeable membrane that is not subjected to any substantial biodegradation during use under practical circumstances.
- the polymer is preferably non-biodegradable, whereby is understood that the polymer does not become disintegrated during use under practical circumstances.
- the emitter cell is characterised by a ratio between i) the amount of tracer moiety released per time unit, and ii) the amount of assayable compound released per time unit, that is essentially the same under practical circumstances.
- the emitter cell may preferably comprise at least one further selectively permeable membrane.
- the selectively permeable membrane and the at least one further se- lectively permeable membrane may have essentially identical permeability properties, or the permeability of said selectively permeable membrane may be different from the permeability of at least one of said further selectively permeable membrane.
- the selectively permeable membrane of the emitter cell and/or the at least one further selectively permeable membrane preferably has a diffusion coefficient in the range of from 10 "13 to 10 "6 cm 2 /sec, such as in the range of from 10 "13 to 10 "11 cm 2 /sec, for example from 10 "11 to 10 "9 cm 2 /sec, such as from 10 "9 to 10 "6 cm 2 /sec.
- the predetermined environment is preferably selected from a soil, a sediment of an agricultural field, and a groundwater reservoir.
- any aqueous sub-surface environment capable of being brought into contact with said assayable compound and/or said tracer moiety is useful.
- the predetermined environment may be any naturally occurring environment wherein "in situ" analysis of the assay- able compound can be carried out.
- the amount of tracer inside of the emitter is at least 1 mg/litre and preferably less than 10000 mg/litre, such as at least 5 mg/litre and preferably less than 5000 mg/litre, for example at least 10 mg/litre and preferably less than 2000 mg/litre, such as at least 25 mg/litre and preferably less than 2000 mg/litre, for example at least 50 mg/litre and preferably less than 1000 mg/litre, such as at least 100 mg/litre and preferably less than 1000 mg/litre, for example at least 200 mg/litre and preferably less than 1000 mg/litre, such as at least 300 mg/litre and preferably less than 1000 mg/litre, for example at least 350 mg/litre and preferably less than 1000 mg/litre, such as at least 400 mg/litre and preferably less than 1000 mg/litre, for ex- ample at least 500 mg/litre and preferably less than 1000 mg/litre.
- the assayable compound is preferably present in said composition in an amount of at least 0.01 g/litre and preferably less than 1000 g/litre, for example at least 0.05 g/litre, such as at least 0.1 g/litre, for example at least 0.2 g/litre, such as at least 0.5 g/litre and preferably less than 1000 g/litre, for example at least 1 g/litre and preferably less than 100 g/litre, such as at least 5 g/litre and preferably less than 100 g/litre, for example at least 10 g/litre and preferably less than 100 g/litre, such as at least 15 g/litre and preferably less than 100 g/litre, for example at least 20 g/litre and preferably less than 75 g/litre, such as at least 25 g/litre and preferably less than 75 g/litre, for example at least 30 g/litre and preferably less than 75 g/litre, such as at least 40 g/litre and preferably less than 75 g/litre, for example at least 45
- the relative change in the concentration of the assayable compound and/or the tracer moiety comprised in the compartment of the cell is less than 20 percent over 48 hours, such as less than 15 percent over 48 hours, for example less than 10 percent over 48 hours, such as less than 8 percent over 48 hours, for example less than 6 percent over 48 hours, such as less than 4 percent over 48 hours, for example less than 2 percent over 48 hours, such as less than 1 percent over 48 hours, for example less than 0.5 percent over 48 hours, such as less than 0.1 percent over 48 hours.
- the concentration of said assayable compound and/or said tracer moiety in the composition comprised in said compartment may be kept substantially unchanged by dissolving a solid form of said assayable compound and/or a tracer moiety also comprised in said compartment.
- the solid form of said assayable compound is preferably comprised in a fluid permeable or liquid permeable matrix such as e.g. a nylon mesh.
- a fluid permeable matrix such as e.g. a nylon mesh.
- the assayable compound is contacted by a fluid permeable matrix capable of releasing said assayable compound into said fluid composition.
- the mesh size of said fluid permeable matrix is at least 1 ⁇ m and preferably less than 100 ⁇ m, such as at least 10 ⁇ m and preferably less than 80 ⁇ m, such as at least 10 ⁇ m and preferably less than 60 ⁇ m, for example at least 20 ⁇ m and preferably less than 50 ⁇ m.
- the device according to the invention may comprise emitter cells comprising the same or different assayable compounds and/or the same or different tracer moieties.
- Figure 8. 2,4,5-T dissolution experiments.
- A measured concentrations versus time;
- B dissolved mass versus time;
- C dissolved mass versus time;
- D calculated dissolu- tion rates at 22°C versus measured dissolution rates at 8°C for initial herbicide weights of 0.83 g and 1.39 g, respectively.
- Figure 9 Atrazine dissolution experiments.
- A measured concentrations versus time;
- B dissolved mass versus time;
- C dissolved mass versus time;
- D calculated dissolu- tion rates at 22°C versus measured dissolution rates at 8°C for initial herbicide weights of 0.57 g and 1.04 g, respectively.
- Figure 10 DNOC dissolution experiments.
- A measured concentrations versus time;
- B dissolved mass versus time;
- C dissolved mass versus time;
- D calculated dissolution rates at 22°C versus measured dissolution rates at 8°C for initial herbicide weights of 0.88 g and 1.08 g, respectively.
- FIG. 11 (A) Experimental setup for the field experiment. (B) Close-up of the diffusive emitter used in the DNOC experiment.
- FIG. 12 (C 2A5 . T / C HTO )-ratios versus approximate residence time for the 2,4,5-T field experiment, day 145 and 241.
- the values for the source wells represent one filter at 3.5 mbs, whereas the values for the multilevel samplers are averages for 4 filters (3.2, 3.4, 3.6, and 3.8 mbs).
- the bold, solid lines are linear regression lines.
- FIG. 13 (C Atrazine / C HTO )-ratios versus approximate residence time for the atrazine field experiment, day 21 and 200.
- the values for the source wells represent one filter at 3.5 mbs, whereas the values for the multilevel samplers are averages for 4 filters (3.2, 3.4, 3.6, and 3.8 mbs).
- the bold, solid lines are linear regression lines.
- Figure 14 (C Atrazine / C HTO )-ratios versus time for the source wells and multilevel samplers located 0.2 m, 0.4 m, 0.6 m, 1.0 m, and 1.5 m downgradient.
- the values for the source wells represent one filter at 3.5 mbs, whereas the values for the multilevel samplers are averages for 4 filters (3.2, 3.4, 3.6, and 3.8 mbs).
- Figure 15 (C DNO c / C HTO )-ratios versus approximate residence time for the DNOC field experiment, day 25 and 192.
- the values for the source wells are averages for three filters at 3.25, 3.5, and 3.75 mbs, whereas the values for the multilevel samplers are averages for 4 filters (3.2, 3.4, 3.6, and 3.8 mbs).
- Figure 16. Measured and calculated concentrations of dichlobenil and HTO in source wells A1-A5 versus time from onset of the experiment. Values represent averages of filters in 3.2, 3.4, 3.6, and 3.8 mbs for all five source wells.
- Figure 17 Break-through curves for HTO and dichlobenil in multilevel samplers located at 1.5, 3.0, 5.0, and 10.0 m downgradient distance from the source wells. Values represent averages of 4 filters in 3.2, 3.4, 3.6, and 3.8 mbs for all multilevel samplers located within the plume at a given downgradient distance.
- the following herbicides were used: 2,4,5-T (2,4,5-trichlorophenoxy acetic acid), 97% pure from Aldrich, atrazine (6-chloro-N-ethyl-N-(1-methylethyl)-1,3,5-triazine- 2,4-diamine), 99% pure from Novartis, DNOC (4,6-dinitro-2-methyl-phenol), 98% pure from MERCK Schuckardt, and dichlobenil (2,6-dichlorobenzonitrile), 98% pure from Fluka Chemicals.
- the tritiated water had a specific activity of 185 MBq/mL and was obtained from Amersham LIFE SCIENCE.
- the first HTO-experiments consisted of two flow-through reactor experiments of 6 months duration performed under identical experimental conditions.
- the emitters contained 17 mL of 341 mg/L HTO, and the water flow rate through the reactor was
- the pump was turned off and the reactors emptied.
- the reactors were then refilled with millipore water and placed in the refrigerator at 8°C without stirring.
- the emitters were cut open, and the HTO concentrations were determined. Since there was no flow through the reactors in this part of the experiments, it was possible to determine the concentration in the emitter bag at 4350 h from a mass balance.
- the emitter HTO concentrations had declined with almost 40% during the first 4350 h, whereas the effluent concentrations remained essentially constant. Accordingly, the steady-state diffusion coefficient at 4350 h was ⁇ 1.2 ⁇ 10 "10 cm 2 /s. The reason for the increasing diffusion coefficient is discussed below.
- the distance between the emitter surface and the reactor wall is -1.5 cm. If we assume that ideal mixing is accomplished in the system with 700 rpm, the effect of a diffusive boundary layer of this thickness corresponds to a difference of 1% only (Arildskov 2000). Evidently, a surface gel layer is therefore formed, and this gel layer affects the transfer of water molecules from the polymer surface into the water phase.
- the steady-state specific fluxes through the emitter walls were calculated from Fick's Law to be 14.6 ⁇ g d _1 cn ⁇ 2 for experiment 1 and 16.4 ⁇ g d _1 cm -2 for experiment 2.
- emitter concentrations 111 mg/L and 123 mg/L were measured for experiment 1 and 2, respectively, showing that the differences in specific flux were due to differences in herbicide dissolution rates.
- the corresponding diffusion coefficients were 1.14 and 1.16 ⁇ 10 -8 cm 2 /s, respectively.
- the transient period is short, lasting only -25 h, and no initially enhanced concentrations are observed.
- the steady-state flux of atrazine through the emitter membrane was 4.5 ⁇ g d _1 cm "2 . After 3500 h, the emitter was cut open and the atrazine concentration measured. The concentration was 23.8 mg/L, corresponding to a diffusion coefficient of 1.64 ⁇ 10 "8 c ⁇ rVs.
- DNOC The laboratory DNOC experiment was performed similarly to the atrazine experiment described above. However, DNOC was chosen as a model compound for the investigation of the effect of the diffusive boundary layer (e.g. Schlichting, 1968) on the diffusion of pesticide molecules through the polymer membrane. Therefore, the stirring rate was varied during the experimental period. Experimental conditions and results are listed in Table 2. The effluent concentration versus time is shown in Figure 5C. After decreasing the stirring rate, a pronounced delay in attaining a new steady-state concentration was observed. This delay probably reflected the development of a (thicker) gel layer on the polymer surface. It is clear that the effect of the DBL is of major importance for DNOC.
- the transient period lasts for -4 days, and the steady-state flux of dichlobenil through the emitter membrane was 10.23 ⁇ g d _1 cm -2 .
- the emitter was cut open and the dichlobenil concentration measured. The concentration was 6.95 mg/L, corresponding to a diffusion coefficient of 2.57x10 '7 cm 2 /s.
- each of the six nylon nets were fixed to the plastic cap using a stainless steel hook. After 48 h of preconditioning in millipore water in order to dissolve the most soluble fraction of each herbicide and thereby avoid significant variations in herbicide surface area at the beginning of the experiments, each net was submerged into a flask filled with 130 mL of pure millipore water. No mixing was applied.
- the dissolution rate is:
- Dissolution rates for the herbicides at 8°C were determined at a number of concentrations. Plots of measured rates at 8°C versus calculated rates for 22°C (Equation 4) are shown at Figures 9 - 11 , (C) and (D). It can be seen that linear fits provide a reasonable approximation, particularly for the 2,4,5-T dissolution data, providing a means for estimation of dissolution rates at 8°C. The equations for the linear fits and the correlation coefficients are shown at the figures.
- the possibility of calculating the dissolution rate as a function of concentration is providing a means of estimating the emitter herbicide concentration when the total flux through the emitter membrane is known.
- the gradient is approximately ten (10) per thousand (o/oo) and virtually unaffected by the fluctuating groundwater table, resulting in an average groundwater velocity at 3-4 mbs of -100 m/yr determined from breakthrough curves for tritiated water (Arildskov, unpublished data).
- the dominant redox processes are iron- and sulfate reduction from 3-3.5 mbs and sulfate reduction from 3.5-4 mbs (Arildskov et al., submitted).
- the diffusive emitters were installed in a row, Fence A, approximately perpendicular to the groundwater flow direction, consisting of 10 adjacent 2 inch (5.08 cm) inner diameter source wells with the screens located from 3-4 mbs. To remove possible flow obstructions by the well screens, the wells were dry-pumped several times before their use. After experiencing clogging of the well screens due to precipitation of iron (hydr)oxides, the well pipes were flushed with nitrogen and sealed with butyl rubber stoppers after submerging the emitters.
- Multilevel samplers with sampling points at 3.2, 3.4, 3.6, and 3.8 mbs were installed during the experiments at horizontal distances 0.2, 0.4, 0.6, 1.0, 1.5, 3.0, 5.0 and 10.0 m downgradient of Fence A. All samples were collected using a 10 mL polypropylene (PP) syringe (B-D ® Plastipak, Becton Dickinson) fitted with a three-way valve. To remove residual water from the PTFE tubing, the first mL was discarded, after which 5 mL of sample was collected and filtered through a 0.2 ⁇ m PTFE-filter (Advantec/MFS 13HP).
- PP polypropylene
- B-D Plastipak, Becton Dickinson
- the difference corresponded to a factor of 2-3 which could be explained by differences in temperature and mixing rate.
- the field derived values were in general a factor of 10 lower than in the laboratory. This could only be partly explained by differences in temperature and mixing rate.
- the same observation was done by Arildskov and Devlin (2000) who released PCE through nylon tubing to another aquifer. Therefore, the deviations seems larger for low polarity molecules and not aquifer specific. Nevertheless, if the difference is taken into ac- count, laboratory derived diffusion coefficients can be used to design field release system that would suit most practical applications.
- the herbicide to tritiated water ratios in downgradient multilevel samplers were stable for the herbicides 2,4,5-T and atrazine, which were not degraded in the test aq- uifer within a residence time of -6 days.
- the system was consistent enough to demonstrate first-order degradation of DNOC without the detection of degradation products.
- sorption of dichlobenil in the aquifer could be measured by comparison of break-through curves for the herbicide and tritiated water, providing a means for calculating the retardation factor.
- both abiotic degradation and sorption have been detected by use of the passive diffusive emitters.
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Abstract
The present invention provides an emitter cell comprising a compartment comprising a fluid composition comprising at least one of a) an assayable compound, and b) a tracer moiety, or a combination of both, wherein said composition comprised in said compartment is separated from a predetermined environment by at least one selectively permeable membrane capable of bringing at least one of said a) and b), when present, or a combination of both, into contact with said predetermined environment, and wherein, when a) is present, at least one of said a) and b) is brought into contact with said predetermined environment by means of passive diffusion. There is also provided a method for monitoring an assayable compound, including a method for monitoring the sorption and/or degradation of said compound. The present invention is useful for monitoring pesticides in groundwater reservoirs.
Description
Device and method for bringing a compound into contact with an environment
Technical field
The present invention pertains to a device and a method for releasing a compound, preferably a pesticide, into a predetermined environment, preferably a subsurface reservoir. The device and the method is useful for monitoring the degradation or sorption of the released substance in the environment. The invention will be useful for generating data on the degradation or sorption of e.g. pesticides in an environment. The data can be evaluated by regulatory authorities prior to decisions concerned with e.g. issuance of marketing authorisations.
Background of the invention
Pesticides are a generic term comprising a large number of completely different compounds used for the control of weeds, harmful insects etc. Pesticides are divided into different groups, determined by the target. The most common of these groups are herbicides against weeds, insecticides against insects, and fungicides against fungi.
Pesticides such as chlorinated hydrocarbons, organophosphorus pesticides, phe- noxy acids, triazines, thiocarbamates and captan have all been developed and used during the past decades in an attempt to control weeds, insects and fungi. Even though many of the pesticides have been banned for a number of years, some of them are now being detected in groundwater. This is causing a problem as the access to groundwater reservoirs for drinking water purposes is restricted. Also, the groundwater may require extensive purification.
Pesticides are continually being developed by the agrochemical industry, and a new generation of pesticides such as synthetic pyrethroides, sulfonylureas and benzim- idazoles have been developed in recent years. The toxicological and environmental behaviour of such pesticides has to be tested, before they can be registered. These
tests are routinely performed by the agrochemical industry. Proper and accurate testing methods are required in order to document the environmental effects of using the pesticides.
Pesticide contamination of surface- and groundwater may be caused by improper handling of the pesticides or result from normal agricultural practices. Pesticides are not only toxic to the target organisms, and it has been established that in some cases only about 1 % of the total amount of pesticide is effectively utilized (Dahi et al. (1989): Laarebog i Vandforurening med Miljøgifte (in Danish), Technical Univer- sity of Denmark). The environmental effect of the use of pesticides depends largely on the annually applied quantity, the concentration, the toxic effect of the pesticide, and the resistance towards degradation in soils and water (Beitz et al., 1994, (Ed.: H. Bόrner): Occurrence, toxicological and ecotoxicological significance of pesticides in Ground and Surface Water, p. 3-56).
The toxic effect of pesticides can be evaluated from tests, in which predetermined organisms are influenced by different doses during a certain period of time (normally from 72 to 96 hours). The toxicity can be measured from one or more of the following:
1 ) LCS0: The concentration, which results in 50% mortality among the test organisms.
2) LD50: The dose (e.g. oral dose), which results in 50% mortality among the test organisms. 3) EC50: The concentration, which results in 50% inhibitance of e.g. algae production.
4) NOEC: Maximum concentration, which results in no visible effect on the test organisms.
Pesticide degradation processes may be abiotic or biotic. Considering pesticide degradation processes in general, non-redox reactions are typically abiotic (McNab & Narasimhan (1994): Degradation of Chlorinated Hydrocarbons and Groundwater Geochemistry: A Field Study. Environ. Sci Technol., 28, p. 769-775). Both abiotic
and biotic degradation processes can be influenced by soil parameters such as particle distribution, mineral composition, organic matter content, humidity, pH, temperature and redox potential. In addition, biotic processes are affected by the bio- mass, the composition of the microbial population, and the availability of nutrients. Microbial degradation of pesticides occurs much more frequently than abiotic degradation. As abiotic degradation products are much the same as those of enzymati- cally catalysed processes, it may be difficult to distinguish between abiotic and biologic degradation.
Biotic processes include processes in living organisms or processes catalysed by enzymes inside or outside living cells. Microbial degradation of a large number of pesticides have been demonstrated, and several pesticide degrading microorganisms have been isolated. Microorganisms capable of metabolising pesticides gain energy thereby, and the pesticides are degraded and, normally, to some degree mineralised into low molecular weight inorganic products like CO2, H20 and CI".
Complete mineralisation of pesticides in aquifers is a complicated process, where typically both biotic and abiotic factors are involved. From an environmental point of view it is important whether a pesticide can be metabolised, as microbial growth is known to speed up pesticide degradation.
The biodegradability of pesticides is normally characterized by their half lives. However, this presupposes that the degradation follows first-order kinetics, and this in turn presupposes that the degradation rate is proportional to the concentration of residual pesticide. A pseudo first-order degradation requires a very low pesticide concentration (which is usually found in groundwater), or a high pesticide degrading potential. At low substrate concentration, diffusion may be the limiting factor for the substrate available to the microorganisms. Also the rate constant depends on the biomass, and the pesticide must be the sole carbon source for the degrading organisms.
Obviously, half life is not a very appropriate way to compare the degradability of different pesticides. Firstly, as mentioned before, the degradation has to follow first order kinetics for all pesticides compared. Secondly, a number of parameters such as temperature, humidity and pH have to be fixed. Furthermore, the experiments
should be carried out in darkness to avoid photodegradation. Finally, and most problematic, the degrading biomass may be able to degrade some pesticides more or less easily, while other compounds may even be toxic to the microorganisms. Therefore, results obtained in one type of sediment are not readily comparable with results from sediment taken from another environment. Also, the redox conditions have to be accounted for, as some pesticides are only degradable in the presence of oxygen, while degradation of other pesticides requires reduced conditions.
Whereas half lives may in some circumstances be used in the laboratory to investi- gate the influence of different parameters on the degradation of one single pesticide, it is required that one parameter (e.g. the temperature) can be varied, while e.g. pH and humidity is fixed. Other experimental conditions such as redox state, biomass and light intensity must also be identical. Even though it is common practice to compare degradability of pesticides by measuring their half lifes, it is at best only a rough estimate. This represents a serious limitation of the state of the art methods directed to the assessment of the degradability of different pesticides.
It should also be noted that half lives concern only the degradation of the parent compound, and therefore provide no information on the formation of metabolites. Since metabolites may well be no less hazardous than the parent compound, rates of total mineralisation are much more relevant from an environmental point of view. For both abiotic and biotic degradation processes, the formation of intermediates or metabolites makes it impossible to measure the amount of pesticide mineralised at a given time point by plotting pesticide concentration versus time. Therefore, it is convenient to define two types of degradation rates: one based on the degradation of the parent pesticide (primary degradation rate), and another based on formation of CO2 (mineralisation rate), if oxygen is available. The difference between these rates will depend on the formation of metabolites together with sorption and accumulation of pesticide in the biomass, which must also be accounted for. Many pesti- cides disappear relatively fast in nature, but they are only partially degraded, resulting in the formation of various metabolites. If pesticides are totally mineralised, the end product is primarily C02. However, it has been demonstrated that far from all pesticides are mineralised, and the formation of stable degradation products with a chemical structure very similar to that of the parent pesticide can occur.
In summary, microbial degradation of pesticides in aquifers is the main source of pesticide mineralisation. The major mechanisms are redox reactions (in the case of pesticide degradation mainly biotic processes) and hydrolysis (both biotic and abi- otic). In most of the degradation processes the microorganisms cannot obtain carbon or nutrients for growth, but only some amount of energy.
Compared to surface sediments, the number of microorganisms in aquifers is very low. Many studies indicate that the biomass is one of the essential parameters de- termining the rate of pesticide degradation. Other parameters of major influence are:
- Humidity is possibly the most important factor next to the number of microorganisms. This is due to a higher bioreactivity in humid environments because sub- strates and nutrients are transported much more readily in such environments.
- The temperature strongly influences both abiotic and biotic degradation processes. Typically, at about 0°C, no degradation occurs at all, while the rate of a pure chemical process will increase with increasing temperature. The same can be said of biotic processes, with the exception that such processes have a temperature optimum - typically in the range of 20-40°C, and at higher temperatures the activity of the microorgarusms strongly decreases.
- pH has an indirect influence on biotic degradation, since most microorganisms are most comfortable at neutral pH. However, some hydrolytic degradations are favoured at low as well as high pH.
- The redox potential is of major importance, since some pesticides can only be degraded in the presence of oxygen while others require reduced conditions. How- ever, pesticides such as nitroaromatics may be degraded under both aerobic and anaerobic conditions, although through different degradation pathways.
It is clear that it is essential to take into account the above-listed factors when determining the environmental effects of using a given pesticide. State of the art labo-
ratory tests are often inadequate for performing such a determination. An accurate and reliable testing method requires that the testing takes place in situ, i.e. on site at a suitable, predetermined location.
The present invention makes it possible to follow the transport and/or the degradation and/or the sorption of e.g. a pesticide in a groundwater reservoir. The invention provides a simple way for determining if a pesticide is either bound to a sediment (sorption), if a pesticide is maintained in a groundwater reservoir, or if a pesticide is degraded, and in the latter case, if the degradation is caused at least partly by mi- croorganisms. Such a determination of the possible outcome of using pesticides is essential for evaluating whether or not the pesticide in question should be granted a marketing authorisation. Accordingly, the present invention represents an important commercial value, as there do not exist for the present time a sufficiently reliable method that is capable of evaluating for example the degradation and transport of pesticides in a groundwater reservoir.
The traditional analysis and assays are not sufficient for evaluating the consequences of using pesticides. The inadequate state of the art test procedures lead in turn to an insecurity concerning the quality of the groundwater. By using the present method it will be possible to minimise significantly any uncertainty associated with the use of pesticides. This is all the more so, if the method pertaining to the present invention is introduced as an international standard for the evaluation of the consequence of using a given pesticide.
The closest prior art (US 5,605,634 Mackay & Wilson; University of Waterloo) describes a method for discharging a substance to the groundwater. According to US 5,605,634 a low density polyethylene (LDPE) tubing can be used. The tubing has a thickness of 0.33 mm. This thickness only allows passage of solutions consisting of small, low polarity molecules in sufficient amounts. There is used a pump in the dis- closed method, and, following introduction of a substance from a surface reservoir, the solution containing that substance is circulated in the LDPE tube and returned to a reservoir.
Several prior art methods exist for the determination of transport or degradation or sorption of a substance in a groundwater reservoir. One method is based on pumping a substance, for example a pesticide, and a tracer into a groundwater reservoir. The degradation and/or flow of the substance and/or the tracer can then be followed by state of the art monitoring techniques. This method has several drawbacks. First of all, it is difficult during prolonged periods of time to discharge - by means of pumping - a constant amount of a substance and tracer into the reservoir, since a pump will not be running sufficiently evenly over long periods of time, and since a problem with the pump inevitably gives rise to a major problem with both discharging the substance and handling of the generated data. Secondly, the system is dependent on electricity - a resource often not available at remote locations - and ordinary maintenance, and thirdly, the pumping cannot avoid disturbing the natural flow conditions on the locality in question.
Another method requires isolation of a sediment from a groundwater reservoir and transfer of the sediment from the reservoir to closed laboratory incubations. It is important, but quite impossible under practical conditions, that the conditions in the laboratory and in the groundwater reservoir are identical. In the laboratory the sediment is supplemented with an aqueous solution of a pesticide, and degradation or sorption of the pesticide over time is monitored. It is clear that this method is a closed, static system while an aquifer is a dynamic system due to the natural groundwater flow with the possibility of exchange of e.g. essential nutrients with the surroundings. Also, in laboratory incubations the groundwater chemical conditions may be changed quite radically during the time in which the experiments take place. It is also a problem that the oxidative/reductive properties of the sediment may change during sample isolation, storage and analysis in the laboratory. It is difficult for an anaerobic sediment sample not to be contaminated by oxygen during isolation, storage or analysis. Also, transfer of the sediment cannot avoid affecting the microorganisms that are present in the sediment, and the microorganisms may for example be subjected to alterations affecting their growth and contact with nutrients, light, temperature and redoxpotential.
In an attempt to minimise the weaknesses of the above mentioned methods it has been attempted to combine elements from each method. Accordingly, a sediment
core has been taken out and placed in a laboratory at groundwater temperature and contacted with an artificial flow of reservoir groundwater and a non-reactive tracer and a pesticide to be tested. The flow of the groundwater through the sediment was supposed to simulate the natural conditions on the locality from which the sediment core was isolated. The disadvantages of this combined method is that the environment is still disturbed during the isolation of the sediment. Also, the flow direction is not necessarily the same as under the natural conditions, the total volume of a sediment capable of being investigated in this way is very limited, and the method cannot be expected to be representative for the conditions characterising the natu- ral groundwater reservoirs on the locality from where the sediment was isolated. Another major weakness of this method is that it is very complicated to carry out such experiments under anaerobic conditions. This is all the more critical for sediments isolated from anaerobic environments.
A need exists for a simple and accurate method for determining the fate of a pesticide in a groundwater reservoir.
The present invention concerns a device for passively releasing a substance to an environment and a method for determining the degradation and/or sorption of the substance in question in the environment. In its presently preferred form the invention is useful for analysing the degradation and/or sorption of organic compounds in an environment such as a natural groundwater reservoir. The invention is particularly useful for analysing organic compounds including pesticides that are moderately polar and preferably less polar than water. The device according to the inven- tion does not require any maintenance, or only a minimal maintenance, and it is simple and economical to install in any given locality of interest.
The invention makes it possible to determine - without any further experiments or analysis - the degree to which a given pesticide might be adsorbed/absorbed to a sediment or, alternatively, degraded, and in the latter case, if such degradation takes place by purely abiotic means or if it is being catalysed by microorganisms.
It is an object of the present invention to provide a method which is based or substantially based on passive diffusion and does not involve using a pumping device
that requires maintenance after initial establishment. It is a further object of the present invention to provide a mechanism for releasing in constant amounts or essentially constant amounts a pesticide and/or a tracer from the same discharging source. This makes it possible to evaluate if the pesticide in question is e.g. not af- fected by the environmental conditions, or if the pesticide is e.g. sorbed or degraded, and if degraded, if degradation takes place by biotic or abiotic degradation pathways. The present invention solves the problems associated with the prior art methods listed herein above.
Summary of the Invention
In a first aspect there is provided an emitter cell comprising
i) a compartment comprising a fluid composition comprising at least one of a) an assayable compound, and b) a tracer moiety, or a combination of both,
ii) wherein said composition comprised in said compartment is separated from a predetermined environment by at least one selectively permeable membrane capable of bringing at least one of said a) and b), when present, or a combination of both, into contact with said predetermined environment, and
iii) wherein, when a) is present, at least one of said a) and b) is brought into contact with said predetermined environment by means of passive diffusion.
In another aspect the present invention pertains to an emitter cell comprising
i) a compartment comprising a fluid composition comprising at least one of a) an assayable compound, and b) a tracer moiety, or a combination of both,
ii) wherein said composition comprised in said compartment is separated from a predetermined environment by at least one selectively permeable membrane capable of bringing at least one of said a) and b), when present, or a combination of both, into contact with said predetermined environment by means of passive diffusion.
Yet another aspect of the invention relates to a device comprising a plurality of operably linked emitter cells according to the invention.
A further aspect of the invention pertains to a kit comprising the emitter cell according to the invention and/or the device according to the invention in combination with detection means for detecting one or more of said assayable compound and said operably linked detectable substance and said tracer moiety and said further tracer moiety.
In yet another aspect the present invention relates to a method for monitoring at least one assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of:
i) providing at least one assayable compound and/or an operably linked detectable substance,
ii) providing an emitter cell according to the invention or a device according to the invention,
iii) providing a predetermined environment in which the assayable compound and/or an operably linked detectable substance can be monitored over time,
iv) providing means for detecting said assayable compound and/or an operably linked detectable substance,
v) introducing said assayable compound and/or an operably linked detectable substance into a compartment of said emitter cell,
vi) introducing said emitter cell comprising said assayable compound and/or an operably linked detectable substance into said predetermined environment,
vii) releasing said assayable compound and/or an operably linked detectable substance comprised in said emitter cell into said environment under controllable conditions, and
viii) monitoring said assayable compound and/or an operably linked detectable substance in said predetermined environment by means of said detection means.
A further aspect of the present invention pertains to a method for monitoring at least one assayable compound and/or an operably linked detectable substance in a predetermined compartment, said method comprising the steps of:
i) providing at least one assayable compound and/or an operably linked detectable substance,
ii) providing an emitter cell according to the invention or a device according to the invention,
iii) providing a predetermined compartment in which the assayable compound and/or an operably linked detectable substance can be monitored over time,
iv) providing means for detecting said assayable compound and/or an operably linked detectable substance,
v) introducing said assayable compound and/or an operably linked detectable substance into said predetermined compartment of said emitter cell or a further compartment of said device,
vi) introducing said emitter cell comprising said assayable compound and/or an operably linked detectable substance into a predetermined environment,
vii) bringing said assayable compound and/or an operably linked detectable substance comprised in said emitter cell into contact with said predetermined environment under controllable conditions, and
viii) monitoring said assayable compound and/or an operably linked detectable substance in said predetermined compartment by means of said detection means.
In an even further aspect there is provided a method for monitoring the sorption of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the sorption of said assayable compound and/or said operably linked detectable substance in said predetermined environment.
In a still further aspect there is provided a method for monitoring the biotic degradation of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the biotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined environment.
In yet another aspect there is provided a method for monitoring the biotic degradation of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the biotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined compartment.
A still further aspect of the invention pertains to a method for monitoring the abiotic degradation of an assayable compound and/or an operably linked detectable sub-
stance in a predetermined environment, said method comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the abiotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined environment.
A further aspect relates to a method for monitoring the abiotic degradation of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the abiotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined compartment.
In another aspect there is provided a method for monitoring the stability of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the stability of said assayable compound and/or an operably linked detectable substance in said predetermined environment.
Yet another aspect pertains to a method for monitoring the stability of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method for monitoring at least one assayable compound and/or an operably linked detectable substance, and at least a further step of monitoring the stability of said assayable compound and/or an operably linked detectable substance in said predetermined compartment.
In a yet further aspect the present invention relates to a method for monitoring at least one tracer moiety in a predetermined environment, said method comprising the steps of:
i) providing at least one tracer moiety,
ii) providing an emitter cell according to the invention or a device according to the invention,
iii) providing a predetermined environment in which the tracer moiety can be monitored over time,
iv) providing means for detecting said tracer moiety,
v) introducing said tracer moiety into said emitter cell,
vi) introducing said emitter cell comprising said tracer moiety into said predetermined environment,
vii) releasing said tracer moiety comprised in said emitter cell into said environ- ment under controllable conditions, and
viii) monitoring said tracer moiety in said predetermined environment by means of said detection means.
In an even further aspect there is provided a method for determining the flow of at least one tracer moiety in a predetermined environment, said method comprising the steps of the method for monitoring at least one tracer moiety, and at least a further step of monitoring the flow of said tracer moiety in said predetermined environment.
In a yet further aspect of the present invention there is provided a method for monitoring at least one assayable compound and/or an operably linked detectable substance in a predetermined compartment, said method comprising the steps of:
i) providing at least one tracer moiety,
ii) providing an emitter cell or the device according to the invention,
iii) providing a predetermined environment in which the tracer moiety can be monitored over time,
iv) providing means for detecting said tracer moiety,
v) introducing said tracer moiety into said emitter cell,
vi) introducing said emitter cell comprising said tracer moiety into said predetermined environment,
vii) releasing said tracer moiety comprised in said emitter cell into said environment under controllable conditions, and
viii) monitoring said tracer moiety in said predetermined environment by means of said detection means,
ix) determining the flow of said tracer moiety in said predetermined environment,
x) providing at least one assayable compound and/or an operably linked detectable substance,
xi) providing an emitter cell according or a device according to the invention,
xii) providing a predetermined environment or a predetermined compartment in which the assayable compound and/or an operably linked detectable substance can be monitored over time,
xiii) providing means for detecting said assayable compound and/or an operably linked detectable substance,
xiv) introducing said assayable compound and/or an operably linked detectable substance into said predetermined compartment of said emitter cell or a further compartment of said device,
xv) introducing said emitter cell comprising said assayable compound and/or an operably linked detectable substance into a predetermined environment,
xvi) bringing said assayable compound and/or an operably linked detectable substance comprised in said emitter ceii into contact with said predetermined environment under controllable conditions, and
xvii) monitoring said assayable compound and/or an operably linked detectable substance in said predetermined environment or predetermined compartment by means of said detection means.
Detailed Description of the Invention
Compartment: Section of emitter cell comprising a composition of matter sur- rounded by a membrane defining a division between said composition comprised in said compartment and an external environment.
Open compartment: Compartment in operably contact with an external source capable of providing said compartment with additional composition of matter and op- tionally maintaining a steady state concentration of said matter comprised in said composition.
Closed compartment: Compartment wherein no contact exists between said composition of matter comprised in said compartment and an external source of said matter.
Assayable compound: Compound capable of being determined or detected either quantitatively or qualitatively by means of any assay suitable for such detection.
Tracer moiety: Moiety retaining identical or substantially identical means for identification at least during assaying or detection.
Predetermined environment: Any environment wherein an assayable compound or a tracer moiety is capable of being released under practical circumstances.
Selectively permeable membrane: Membrane that is permeable for a given substance, and impermeable for other substances. Permeability may be defined on the basis of chemical and/or physical properties of a given substance.
Bringing into contact: Introducing compositions of matter initially present in different locations into the same compartment or environment.
Passive diffusion: Bringing a composition of matter comprised in a closed compart- ment into contact with a composition of matter comprised in a predetermined environment.
Semi-passive diffusion: Bringing a composition of matter comprised in a open compartment into contact with a composition of matter comprised in a predetermined environment.
Detectable label: Substance capable of revealing quantitative or qualitative properties of a moiety or a compound.
Reversibly bound compound or moiety: Compound or moiety capable of existing in a bound as well as an unbound form.
Polymer: Polymer is understood within the ordinary meaning at this term and comprises molecules formed by the union of at least one type of monomer.
Preferred embodiments of the present invention are described in detail below.
The compartment according to the invention may comprise a fluid composition comprising either a) an assayable compound, or b) a tracer moiety, or a combination of both a) and b). The fluid composition comprising said compound and/or said tracer preferably comprises a liquid composition such as e.g. an aqueous solvent.
Accordingly, there is provided in one embodiment an emitter cell wherein a) is brought into contact with said environment by means of passive diffusion in the absence of b). In another embodiment the present invention pertains to an emitter cell wherein a) is brought into contact with said environment by means of passive diffu- sion and b) is brought into contact with said environment by means of semi-passive diffusion. There is also provided an emitter cell wherein a) is brought into contact with said environment by means of semi-passive diffusion and b) is brought into contact with said environment by means of passive diffusion.
It is preferred that the invention relates to an emitter cell wherein both a) and b) are brought into contact with said environment by means of passive diffusion. When both of the assayable compound a) and the tracer moiety b) is brought into contact with said environment by means of passive diffusion, the present invention overcomes the problems associated with prior art solutions to a similar problem. In par- ticular, the present invention renders the use of a pumping source superfluous, and the expenses associated with acquiring and running a pump can be saved. This also eliminates any problems associated with periodically uneven pumping speeds as well as any problems arising when the natural flow on the location is being disturbed by the pumping source.
In the case of only b) being present, there is provided an emitter cell wherein b) is brought into contact with said environment by means of either passive diffusion or semi-passive diffusion in the absence of a). It may be advantageous to initially bring the tracer moiety b) into contact with said external environment in order to deter- mine the flow of groundwater on the location in question. When the flow direction has been determined it is possible to carry out an experiment wherein the assay- able compound a) and optionally also the tracer moiety b) is brought into contact with said external environment. The advantage associated with such a two-step method is that no assayable compound is released in vain, if the direction of the flow of groundwater should be different from that expected.
It is possible to emit tracer only, or initially to emit tracer only, in order to evaluate or analyse in more detail the flow of the groundwater on the location in question. This
is useful when making an assessment of the time it will take before e.g. a pollution is likely to reach a groundwater reservoir being used as a source for drinking water.
Passive diffusion results in bringing the composition comprising the assayable com- pound and/or the tracer moiety into contact with an external environment. Passive diffusion as used herein is normally caused by a concentration gradient, that is different concentrations of said assayable compound and/or said tracer in different locations such as e.g. a compartment and an external environment separated by a boundary such as a membrane comprising a polymer allowing the diffusion to oc- cur. However, a passive diffusion may also be caused by a temperature gradient or a pressure gradient.
In one embodiment the contact is established when the composition comprised in the closed compartment diffuses into the external environment. In another embodi- ment the contacting of the external environment and the composition comprising the assayable compound and/or the tracer moiety occurs in the compartment itself. This is the case when composition of matter from the external environment enters the compartment. However, contacting may also take place in both the compartment and the external environment.
The emitter cell may also comprise a composition comprising at least one further assayable compound or a detectable substance operably linked to at least one of said assayable compound and said further assayable compound. The detectable substance is operably linked as used herein when said assayable compound and/or said further assayable compound is capable of being converted into said detectable substance. The conversion may take place by means of any form of chemical modification, or reaction with a chemical or biological agent including a microorganism. The operable linkage makes it possible to detect said assayable compound and/or said further assayable compound by means of detecting instead said detectable substance. This is particularly relevant in the case of an assayable compound being degraded only very slowly, as the detection of said operably linked detectable substance will nevertheless indicate that degradation of the assayable compound does indeed take place.
The assayable compound and/or the further assayable compound is preferably selected independently from the group consisting of chemical compounds and the group consisting of biological compounds. Chemical compounds shall be understood to comprise any compound made by in vitro synthesis, whereas biological compounds relate to entities such as cells and viruses as well as their metabolites.
Preferred biological compounds are microbial cells selected from the group consisting of eukaryotic microbial cells and prokaryotic microbial cells. Among the pro- karyotic microbial cells, earth bacteria such as Pseudomonas species are preferred, in particular Pseudomonas species such as e.g. Pseudomonas fluorescens.
Preferred chemical compounds are pesticides including herbicides, insecticides and fungicides. One group of preferred pesticides comprise chlorinated hydrocarbons, organophosphorus pesticides, phenoxy acids, triazines, thiocarbamates and ni- troaromatics. Another group of preferred pesticides comprise synthetic pyrethroides, sulfonylureas and benzimidazoles.
It is particularly relevant to perform an assay for any pesticide, including any herbicide, insecticide or fungicide, including any synthetic pyrethroide, sulfonylurea or benzimidazole, and any derivative thereof, suspected of being able to resist degradation in a soil sediment, or suspected of being able to remain in a soil sediment in concentrations or levels above those determined by the authorities as maximum recommendable values. In particular, such non-degradable or "slowly" degraded compounds are likely to enter groundwater reservoirs and render said reservoirs unsuitable for use in ordinary tap water, unless thoroughly cleaned or filtered.
The assayable compound and/or said further assayable compound, when present in water, preferably represents a potential health hazard for human beings, or a compound generally recognised as being undesirable for human and/or animal con- sumption. Such compounds are typically characterised by the authorities according to a LC50 value, indicating the concentration, which results in 50% mortality among the test organisms, a LD50 value indicating the dose (e.g. oral dose), which results in 50% mortality among the test organisms, or the EC50 value providing the concentration, which results in 50% inhibitance of e.g. algae production.
The tracer moiety according to the invention preferably comprises a detectable label. The label must be sensitive enough to facilitate detection or quantification of said tracer during use under practical circumstances. For those reasons, the de- tectable label preferably comprises a radiolabel and/or a fluorescently detectable label. When the tracer moiety comprises a radiolabel, tracer in the form of tritiated water or tracer comprising tritiated water is preferred. This preference is due to the fact that the behaviour of tritiated water would be identical to or resembles the nature of an aqueous solution comprised in the compartment according to the inven- tion. Examples of preferred tracers are 3H HO, 3H20, 2H20, 2H1HO, 3H HO, and
H2 18O. Another tracer capable of being used in combination with the present invention is sulphurhexafluoride, SFe.
One or more of said assayable compound and said further assayable compound and said tracer moiety may be reversibly bound to a solid phase. Reversibly bound shall be understood to comprise any association formed between said solid phase and one or more of said assayable compounds and tracer moiety that does not prevent said compounds or tracer from disassociating or reassociating themselves with said phase by any means of disassociation or reassociation. The solid phase pref- erably comprises a silica gel or a resin, more preferably a silica gel, and preferably only the tracer moiety is reversibly bound to said silica gel forming said solid phase.
The emitter cell according to the invention may comprise a fluid or liquid composition comprising a plurality of different assayable compounds. Accordingly, the com- position may comprise for example from two to ten different assayable compounds, such as from three to eight different assayable compounds, for example from four to six different assayable compounds.
The composition may also comprise at least one further tracer moiety, such as from two to five different tracer moieties, for example three or four different tracer moieties.
The emitter cell comprises a selectively permeable membrane comprising a polymer. Preferred polymers according to the invention are natural or synthetic poly-
mers, such as e.g. polymers comprising nylon and polymers comprising polyethylene. The polymer preferably comprises a compound acting as co-polymer or block co-polymer. Said co-polymer or block co-polymer preferably has the effect of acting as a softening agent at least when comprised in the polymer.
Polyethylene comprising ethylene methacrylate (EMA) as a random co-polymer is particularly preferred. The polyethylene is preferably a low-density polyethylene (LDPE), and the random co-polymer, preferably methacrylate, is preferably present in an amount of from 1 to 25 percent, such as from 12 to 24 percent, for example from 14 to 22 percent, such as from 15 to 21 percent, for example from 16 to 20 percent, such as from 17 to 19 percent, for example about 18 percent. Additionally preferred polymers comprise or at least essentially consist of ethylene vinyl acetate (EVA) or ethylene acrylic acid (EAA).
The selectively permeable membrane comprising a polymer preferably has a thickness of less than about 2.0 millimeter (mm), such as less than about 1.0 mm for example less than 0.8 mm, such as less than about 0.6 mm, for example less than about 0.4 mm, for example less than 0.3 mm, such as less than about 0.2 mm, such as less than about 0.1 mm, for example about 0,075 mm, for example less than about 0.05 mm. A membrane comprising low-density polyethylene comprising ethylene methacrylate as a random co-polymer is preferably used with a thickness of less than 0.5 mm, such as less than 0.1 mm, for example about 0.075 mm.
In one embodiment the polymer is substantially impermeable to charged particles including ionic species. However, it may also be preferred under some circumstances that the polymer is substantially impermeable to low polarity particles and particles that do not comprise any ionic charges. Additionally preferred polymers are polyvinyl alcohol, cellulose acetate, polydimethylsiloxane, polybutadiene, ethyl cellulose, and polymethyl methacrylate. Among these, polyvinyl alcohol, cellulose acetate, polydimethylsiloxane are more preferred because of their diffusive properties.
The polymer may be any polymer that is functionally equivalent to low-density polyethylene (LDPE) comprising a co-polymer, for example a random co-polymer, pref-
erably ethylene methacrylate, in an amount of 18 percent. Functionally equivalent as used herein above denotes that when a polymer other than LDPE comprising ethylene methacrylate as a random co-polymer in an amount of 18 percent, the calculated diffusion coefficient for a given compound is either at least substantially similar to the diffusion coefficient obtained for LDPE comprising ethylene methacrylate as a random co-polymer in an amount of 18 percent, or, alternatively, functionally equivalent shall be understood to mean that any differences observed over time in the amounts of compound released per time unit, is substantially similar to the differences, if any, observed when said compound is released from LDPE com- prising ethylene methacrylate as a random co-polymer in an amount of 18 percent.
It is preferred that when said assayable compound and/or said tracer moiety is released into said predetermined external environment, the concentration of the compound or tracer in the fluid or liquid composition comprised in the compartment is substantially unchanged over time. This is preferably achieved for a closed compartment by including into said closed compartment a solid source comprising said compound and/or said tracer.
The inclusion of a solid source of compound and/or tracer serves the purpose of supplementing the fluid or liquid source of said compound or said tracer comprised in said closed compartment with additional compound and/or tracer. This supplement in the form of the addition to the closed compartment of compound and/or tracer - per time unit - is preferably at least substantially equal to the amount of compound and/or tracer being released - per time unit - into a predetermined exter- nal environment from said closed compartment. In this way, the concentration of said compound or tracer in said fluid or liquid composition is kept at least substantially constant over at least part of the time of releasing said compound and/or said tracer into said environment.
Should any changes in the concentration of said compound or tracer comprised in a fluid or liquid composition occur during the period of time wherein said compound and/or tracer is released into said environment, it is preferred that these changes are compensated for by an adaptation of the composition of said permeable membrane comprising a polymer according to the invention, wherein the term adaptation
is understood to mean any change in the composition of said membrane or polymer capable of maintaining a constant flux of said compound and/or tracer irrespective of any change in their concentration when they are present in a liquid or fluid composition comprised in said compartment. According to one presently preferred hy- pothesis, such adaptations of the composition of the permeable membrane according to the invention preferably occurs by carefully selecting corresponding pairs of at least one polymer and at least one co-polymer, or corresponding pairs of at least one polymer and at least one block co-polymer. Adaptation as used herein may involve that the polymer in question becomes more permeable to the compound and/or the tracer over time. The increased permeability preferably counteracts any decrease in the amount and/or concentration of dissolved compound and/or tracer comprised in the compartment.
Accordingly, it is preferred that either the membrane comprising the polymer ac- cording to the invention does not undergo any significant modifications causing the flux through the membrane of compound and/or tracer to be altered significantly over at least part of the period of time of releasing said compound and/or tracer, or alternatively, it is preferred that the membrane comprising the polymer according to the invention undergoes an adaptation as defined herein above capable of main- taining an essentially constant flux through the membrane of compound and/or tracer over at least part of the period of time of releasing said compound and/or tracer.
The term "at least part of the period of time of releasing said compound and/or tracer" will be understood to exclude any initial period substantially shorter than the total release period, wherein "steady-state" release conditions are being established during said "initial" period. The "initial" period is often referred to as the "transient" period in the art. The length of said initial period preferably amounts to less than 10 percent, for example less than 5 percent, such as less than 2 percent, for example less than 1 percent, such as less than 0.5 percent of the length of the total release period being equal to the period wherein compound and/or tracer is being released or brought into contact with said predetermined external environment.
It is much preferred that the emitter cell is capable of releasing essentially the same amount of assayable compound and/or tracer moiety per time unit under practical circumstances. This uniform release rate will simulate a "steady-state" release system and thus improve data quality and validity.
It is clear that the emitter cell pertaining to the present invention comprises a permeable membrane and optionally a further permeable membrane that is not subjected to any substantial biodegradation during use under practical circumstances. Accordingly, the polymer is preferably non-biodegradable, whereby is understood that the polymer does not become disintegrated during use under practical circumstances.
In one preferred embodiment the emitter cell is characterised by a ratio between i) the amount of tracer moiety released per time unit, and ii) the amount of assayable compound released per time unit, that is essentially the same under practical circumstances.
The emitter cell may preferably comprise at least one further selectively permeable membrane. The selectively permeable membrane and the at least one further se- lectively permeable membrane may have essentially identical permeability properties, or the permeability of said selectively permeable membrane may be different from the permeability of at least one of said further selectively permeable membrane.
The selectively permeable membrane of the emitter cell and/or the at least one further selectively permeable membrane preferably has a diffusion coefficient in the range of from 10"13 to 10"6 cm2/sec, such as in the range of from 10"13 to 10"11 cm2/sec, for example from 10"11 to 10"9 cm2/sec, such as from 10"9 to 10"6 cm2/sec.
The predetermined environment is preferably selected from a soil, a sediment of an agricultural field, and a groundwater reservoir. However, any aqueous sub-surface environment capable of being brought into contact with said assayable compound and/or said tracer moiety is useful. Accordingly, the predetermined environment may be any naturally occurring environment wherein "in situ" analysis of the assay-
able compound can be carried out. However, it is also possible to use the invention under laboratory conditions for analysis of e.g. an assayable compound released into - or being brought into contact with - a sample of a soil or a sediment extracted from or separated from a natural environment.
The amount of tracer inside of the emitter is at least 1 mg/litre and preferably less than 10000 mg/litre, such as at least 5 mg/litre and preferably less than 5000 mg/litre, for example at least 10 mg/litre and preferably less than 2000 mg/litre, such as at least 25 mg/litre and preferably less than 2000 mg/litre, for example at least 50 mg/litre and preferably less than 1000 mg/litre, such as at least 100 mg/litre and preferably less than 1000 mg/litre, for example at least 200 mg/litre and preferably less than 1000 mg/litre, such as at least 300 mg/litre and preferably less than 1000 mg/litre, for example at least 350 mg/litre and preferably less than 1000 mg/litre, such as at least 400 mg/litre and preferably less than 1000 mg/litre, for ex- ample at least 500 mg/litre and preferably less than 1000 mg/litre.
The assayable compound is preferably present in said composition in an amount of at least 0.01 g/litre and preferably less than 1000 g/litre, for example at least 0.05 g/litre, such as at least 0.1 g/litre, for example at least 0.2 g/litre, such as at least 0.5 g/litre and preferably less than 1000 g/litre, for example at least 1 g/litre and preferably less than 100 g/litre, such as at least 5 g/litre and preferably less than 100 g/litre, for example at least 10 g/litre and preferably less than 100 g/litre, such as at least 15 g/litre and preferably less than 100 g/litre, for example at least 20 g/litre and preferably less than 75 g/litre, such as at least 25 g/litre and preferably less than 75 g/litre, for example at least 30 g/litre and preferably less than 75 g/litre, such as at least 40 g/litre and preferably less than 75 g/litre, for example at least 45 g/litre and preferably less than 75 g/litre, such as at least 50 g/litre and preferably less than 75 g/litre.
It is preferred that the relative change in the concentration of the assayable compound and/or the tracer moiety comprised in the compartment of the cell is less than 20 percent over 48 hours, such as less than 15 percent over 48 hours, for example less than 10 percent over 48 hours, such as less than 8 percent over 48 hours, for example less than 6 percent over 48 hours, such as less than 4 percent
over 48 hours, for example less than 2 percent over 48 hours, such as less than 1 percent over 48 hours, for example less than 0.5 percent over 48 hours, such as less than 0.1 percent over 48 hours.
It will be understood that at least when the assayable compound and/or tracer moiety is being brought into contact with said external environment by means of passive diffusion, due to a concentration gradient or otherwise, the concentration of said compound and/or tracer in the composition comprised in the compartment will gradually decrease, unless said assayable compound is confined to said compart- ment, in which case the contacting between said compound confined to said compartment and a composition comprised in a predetermined external environment will take place in said compartment.
When an assayable compound and/or a tracer moiety according to the present in- vention is released from a closed compartment as defined herein, and into an external, predetermined environment, the concentration of said assayable compound and/or said tracer moiety in the composition comprised in said compartment may be kept substantially unchanged by dissolving a solid form of said assayable compound and/or a tracer moiety also comprised in said compartment. This feature rep- resents a significant difference as compared to the pumping systems of the prior art, wherein it is preferred that the concentration of the compound in an open compartment is kept unchanged by means of a pumping source supplementing the open compartment with additional compound already present in a dissolved form.
The solid form of said assayable compound is preferably comprised in a fluid permeable or liquid permeable matrix such as e.g. a nylon mesh. In one embodiment the assayable compound is contacted by a fluid permeable matrix capable of releasing said assayable compound into said fluid composition. The mesh size of said fluid permeable matrix is at least 1 μm and preferably less than 100 μm, such as at least 10 μm and preferably less than 80 μm, such as at least 10 μm and preferably less than 60 μm, for example at least 20 μm and preferably less than 50 μm.
The device according to the invention may comprise emitter cells comprising the same or different assayable compounds and/or the same or different tracer moieties.
List of references
Arildskov, N.P. 2000. Diffusive emitters for investigating the fate of organic contaminants in aquifers. Ph.D. thesis. Department of Geology and Geotechnical Engineering, Technical University of Denmark.
Arildskov, N. P., Devlin, J. F., 2000. Field and laboratory evaluation of a diffusive emitter for semipassive release of PCE to an aquifer. Ground Water, 38: 129- 138.
Arildskov, N. P., Pedersen, P. G. and Albrechtsen, H. -J., 2000. Fate of the herbicides 2,4,5-T, atrazine, and DNOC in a shallow, anaerobic aquifer investigated by in situ passive diffusive emitters and batch laboratory experiments. Ground Water, submitted.
Clausen, L. 2000. Retention of Pesticides in Filter membranes. Journal of Environmental Quality 29, no. 2: 654-657.
Schlichting, H., 1968. Boundary-Layer Theory. 6th ed, McGraw-Hill Book Company, New York.
Figure Legends
Figure 1. (A) Experimental setup for the laboratory experiment. (B) Close-up of the reactor
Figure 2. (A) concentration histories for two flow-through reactor experiments with initial emitter concentrations = 341 mg/L. Q -10 mL/h; A = 40 cm2; T = 22°C; / = 75 μm; stirring rate 300 rpm. (B) concentration histories for the same emitters immersed in a no-flow reactor at 8°C after 4350 h. Reactor volume, Vr = 138 mL.
Figure 3. Concentration histories for flow-through reactor experiments with initial emitter concentrations of HTO within the range 25 - 750 mg/L. Q -10 mL/h; A = 62.4 cm2; T= 22°C; / = 75 μm; no stirring.
Figure 4. (A) concentration histories for a no-flow reactor with stirring rates 0,
200, 300, and 700 rpm. C, = 500 mg/L; A = 63.2 cm2; T = 22°C; / = 75 μm, reactor volume, Vr = 303 mL. (B) calculated diffusion coefficients versus stirring rate.
Figure 5. Concentration histories for flow-through reactor experiments with: (A) two emitters containing 0.34 g solid 2,4,5-T in 17 mL of water. Q -10 mL/h; A = 40 cm2; T =22°C; / = 75 μm; stirring rate 300 rpm. (B) an emitter containing 0.74 g solid atrazine in 41 mL of water. Q = 9.96 mL/h; A = 72 cm2; T = 22°C; / = 75 μm; stirring rate 300 rpm. (C) an emitter containing 2 g solid DNOC in 48 mL of water. Q -10 mL/h; A = 90 cm2; T = 22°C; / = 75 μm; stirring rate 0 - 300 rpm.
Figure 6. Specific DNOC flux versus stirring rate. The bold, solid line is a linear regression line (R2=0.996), and the error bars represent ± one standard deviation.
Figure 7. Concentration versus time curve for a laboratory flow-through reactor experiment with an emitter containing 1.8 g solid dichlobenil in 44 mL of water. Q = 9.86 mL/h; A = 81 cm2; T- 22°C, / = 7.5 x 10"3 cm; stirring rate 300 rpm.
Figure 8. 2,4,5-T dissolution experiments. (A) measured concentrations versus time; (B) dissolved mass versus time; (C) and (D) calculated dissolu- tion rates at 22°C versus measured dissolution rates at 8°C for initial herbicide weights of 0.83 g and 1.39 g, respectively.
Figure 9. Atrazine dissolution experiments. (A) measured concentrations versus time; (B) dissolved mass versus time; (C) and (D) calculated dissolu-
tion rates at 22°C versus measured dissolution rates at 8°C for initial herbicide weights of 0.57 g and 1.04 g, respectively.
Figure 10. DNOC dissolution experiments. (A) measured concentrations versus time; (B) dissolved mass versus time; (C) and (D) calculated dissolution rates at 22°C versus measured dissolution rates at 8°C for initial herbicide weights of 0.88 g and 1.08 g, respectively.
Figure 11. (A) Experimental setup for the field experiment. (B) Close-up of the diffusive emitter used in the DNOC experiment.
Figure 12. (C2A5.T / CHTO)-ratios versus approximate residence time for the 2,4,5-T field experiment, day 145 and 241. The values for the source wells represent one filter at 3.5 mbs, whereas the values for the multilevel samplers are averages for 4 filters (3.2, 3.4, 3.6, and 3.8 mbs). The bold, solid lines are linear regression lines.
Figure 13. (CAtrazine / CHTO)-ratios versus approximate residence time for the atrazine field experiment, day 21 and 200. The values for the source wells represent one filter at 3.5 mbs, whereas the values for the multilevel samplers are averages for 4 filters (3.2, 3.4, 3.6, and 3.8 mbs). The bold, solid lines are linear regression lines.
Figure 14. (CAtrazine / CHTO)-ratios versus time for the source wells and multilevel samplers located 0.2 m, 0.4 m, 0.6 m, 1.0 m, and 1.5 m downgradient.
The values for the source wells represent one filter at 3.5 mbs, whereas the values for the multilevel samplers are averages for 4 filters (3.2, 3.4, 3.6, and 3.8 mbs).
Figure 15. (CDNOc / CHTO)-ratios versus approximate residence time for the DNOC field experiment, day 25 and 192. The values for the source wells are averages for three filters at 3.25, 3.5, and 3.75 mbs, whereas the values for the multilevel samplers are averages for 4 filters (3.2, 3.4, 3.6, and 3.8 mbs).
Figure 16. Measured and calculated concentrations of dichlobenil and HTO in source wells A1-A5 versus time from onset of the experiment. Values represent averages of filters in 3.2, 3.4, 3.6, and 3.8 mbs for all five source wells.
Figure 17. Break-through curves for HTO and dichlobenil in multilevel samplers located at 1.5, 3.0, 5.0, and 10.0 m downgradient distance from the source wells. Values represent averages of 4 filters in 3.2, 3.4, 3.6, and 3.8 mbs for all multilevel samplers located within the plume at a given downgradient distance.
Example 1
Laboratory experiments with four different herbicides or tritiated water
Herbicides and tritiated water
The following herbicides were used: 2,4,5-T (2,4,5-trichlorophenoxy acetic acid), 97% pure from Aldrich, atrazine (6-chloro-N-ethyl-N-(1-methylethyl)-1,3,5-triazine- 2,4-diamine), 99% pure from Novartis, DNOC (4,6-dinitro-2-methyl-phenol), 98% pure from MERCK Schuckardt, and dichlobenil (2,6-dichlorobenzonitrile), 98% pure from Fluka Chemicals. The tritiated water had a specific activity of 185 MBq/mL and was obtained from Amersham LIFE SCIENCE.
Laboratory emitter experiments
In the laboratory emitter experiments, the diffusion of HTO or herbicide out of the emitter bags was studied by placing emitters containing HTO or excess solid herbicide in reactors filled with millipore water. The experimental setup is shown in figure 1. The diffusion out of the emitters was monitored by analysis of the HTO or herbi- cide content of the reactor vessel. These experiments were undertaken to test the ability of the emitters to release stable amounts of HTO or herbicide during experimental periods of several months. Also, in order to make laboratory and field derived specific fluxes/diffusion coefficients comparable, the effects of stirring rate and temperature differences were investigated.
Tritiated water
The first HTO-experiments consisted of two flow-through reactor experiments of 6 months duration performed under identical experimental conditions. The emitters contained 17 mL of 341 mg/L HTO, and the water flow rate through the reactor was
-10 mL/h. The experiments were run at room temperature (~22°C) with stirring rate 300 rpm. HTO concentrations in the effluent versus time are shown in Figure 2A. The enhanced values from 0-800 h were probably due to stretching of the polymer, caused by a slight over-pressure inside of the emitter. Stretching increases the dis- tance between the polymer chains and thereby increases the diffusion coefficient. There was a good agreement between the two data sets which indicated that the applied polymer is uniform with respect to the water diffusion coefficient. The diffusion coefficients calculated by Fick's First Law from the steady-state concentrations after 800 h were approximately 8χ10"11 cm2/s.
After 4350 h, the pump was turned off and the reactors emptied. The reactors were then refilled with millipore water and placed in the refrigerator at 8°C without stirring. After 357 h, the emitters were cut open, and the HTO concentrations were determined. Since there was no flow through the reactors in this part of the experiments, it was possible to determine the concentration in the emitter bag at 4350 h from a mass balance. The emitter HTO concentrations had declined with almost 40% during the first 4350 h, whereas the effluent concentrations remained essentially constant. Accordingly, the steady-state diffusion coefficient at 4350 h was ~1.2χ10"10 cm2/s. The reason for the increasing diffusion coefficient is discussed below.
For the final part of the experiments (8°C, no mixing), the diffusion coefficients were determined from the slope of the concentration time curves (Figure 2B). The lower temperature and mixing rate resulted in a diffusion coefficient which was a factor of 2.7 lower.
Fick's First Law predicts that the specific flux through the emitter membrane at steady-state is proportional to the emitter concentration. To confirm this, a series of unstirred flow-through reactor experiments with emitter HTO concentrations in the range 25-750 mg/L were conducted at 22°C. Measured concentrations versus time
are shown in Figure 3. The results and experimental conditions are summarized in Table 1. When preparing the emitters for these experiments, care was taken to avoid a pressure gradient across the membrane, and, accordingly, no enhanced initial concentrations were observed in this series of experiments. The calculated dif- fusion coefficients for the experiments compared well with a mean value of
Table 1. Experimental conditions and results from flow-through reactor experiments with tritiated water. For all experiments, the polymer thickness, / = 7.5 x 10"3 cm, the emitter surface area, A = 62.4 cm2, the temperature is 22°C, and no stirring is applied. Errors represent one standard deviation.
d mg/L) °2 (μg/L) Q (mL/h) D (cm2/s)
25 5.3 +/- 0.4 9.81 +/- 0.05 (6.95 +/- 0.61) x 10'11
100 23.5 +/- 3.4 9.69 +/- 0.07 (7.60 +/- 1.18) x 10"11
250 54.3 +/- 5.2 10.01 +/- 0.0-
500 115.7 +/- 9.8 10.20 +/- 0.0! iι
750 154.6 +/- 18.1 9.94 +/- 0.06 (6.84 +/- 0.87) x 10"11
500, polymer 147.1 +/- 8.9 9.52 +/- 0.05 (9.35 +/- 0.74) x 10"11 washed for 118 days
The increase in water diffusion coefficient of the polymer over time was confirmed by including an emitter made of polymer previously washed in millipore water for
118 days in the experiments. The diffusion coefficient for this emitter was 9.35x10"11 cm2/s or 1.3 times the average for the other experiments, whereas the increase after 180 days in the experiments described above corresponded to a factor of 1.5. The increase could be caused by dissolution of uncopolymerized EMA in the pene- trating water. Some uncopolymerized monomer units are probably present in plastics containing copolymer. Dissolution of polyethylene is more unlikely because of
the hydrophobicity of this polymer. Dissolution was confirmed by DOC measurements on the effluent from two of the flow-through reactor experiments, where trace amounts of DOC were detected. Evidently, the dissolution is a slow process that proceeds over several months.
If the gel layer formed at the outer surface of the emitter due to dissolution of the polymer is too thin to be of practical importance, then the DBL-effect for HTO must be small because the diffusion coefficient for water in the polymer is much lower than the water self-diffusion coefficient. A series of no-flow reactor experiments was carried out with emitter concentration 500 mg/L and stirring rates in the range 0 - 700 rpm. The HTO concentrations versus time are shown in Figure 4A, and calculated diffusion coefficients versus stirring rate can be seen in Figure 4B. The difference in diffusion coefficients between the unstirred experiment and the experiments with 300 and 700 rpm corresponds to increases of 22% and 48%, respectively. The maximum possible boundary layer thickness in the reactors, i.e. the distance between the emitter surface and the reactor wall, is -1.5 cm. If we assume that ideal mixing is accomplished in the system with 700 rpm, the effect of a diffusive boundary layer of this thickness corresponds to a difference of 1% only (Arildskov 2000). Evidently, a surface gel layer is therefore formed, and this gel layer affects the transfer of water molecules from the polymer surface into the water phase.
2,4,5-T
The diffusion of 2,4,5-T out of the emitter bags was studied by placing emitters containing excess solid 2,4,5-T in a flow-through reactor and monitoring the 2,4,5-T concentration in the effluent. The experimental conditions and results are listed in Table 2. Figure 5A shows concentration histories for two experiments with emitters containing 0.34 g solid 2,4,5-T (not encapsulated in nylon net) and 17 mL of millipore water. Enhanced initial concentrations, again caused by a slight over-pressure in the emitter bags, were observed. After -500 h a steady-state was reached, and for the rest of the experimental period of 4350 h, the concentrations in the effluents were stable. The steady-state specific fluxes through the emitter walls were calculated from Fick's Law to be 14.6 μg d_1cnτ2 for experiment 1 and 16.4 μg d_1cm-2 for experiment 2. At the conclusion of the experiments (4350 h), emitter concentrations of 111 mg/L and 123 mg/L were measured for experiment 1 and 2, respectively,
showing that the differences in specific flux were due to differences in herbicide dissolution rates. The corresponding diffusion coefficients were 1.14 and 1.16χ10-8 cm2/s, respectively.
Table 2. Experimental conditions and results from laboratory flow-through reactor experiments with emitters containing solid phase herbicide. For all experiments, the polymer thickness is 7.5 x 103 cm, and the reactor temperature is 22°C.
Herbicide 2,4,5-T Atrazine DNOC Dichlobenil
Emitter surface area (cm2) 40 72 90 81
Emitter volume (cm3) 17 41 48 44
Amount of solid herbicide (g) 0.34 0.74 2.0 1.8
Reactor volume (cm3) 138 303 303 303
Average water flow (mL/h) 10.04 9.96 9.82 9.86
Stirring rate (rpm) 300 300 0-300 300
Steady-state effluent cone. (mg/L) 2.43 1.34 15.2-30.2 3.5
Flux through emitter membrane 40.4 a (μg/d cm2) 14.64 4.45 60.8 b 10.23 78.6 c
Unstirred 150 rpm :300 rpm
Atrazine
Another stirred flow-through reactor experiment aimed at determining specific flux and diffusion coefficient under laboratory conditions was conducted with solid atrazine inside of the emitter. The emitter was cylinder-shaped and larger than those applied in the 2,4,5-T experiments. In order to minimize the vertical concentration gradient inside of the emitter, the solid atrazine was encapsulated in a nylon net fixed along the central axis of the emitter, as illustrated in Figure 1 B. The experimental conditions and results are summarized in Table 2. The effluent concentration versus time in Figure 5B shows a fairly constant steady-state concentration but with
larger fluctuations than for 2,4,5-T. The water flow rate was very stable during the experiment, and the fluctuations must therefore be attributed to analytical uncertainty. The transient period is short, lasting only -25 h, and no initially enhanced concentrations are observed. The steady-state flux of atrazine through the emitter membrane was 4.5 μg d_1cm"2. After 3500 h, the emitter was cut open and the atrazine concentration measured. The concentration was 23.8 mg/L, corresponding to a diffusion coefficient of 1.64χ10"8 cπrVs.
DNOC The laboratory DNOC experiment was performed similarly to the atrazine experiment described above. However, DNOC was chosen as a model compound for the investigation of the effect of the diffusive boundary layer (e.g. Schlichting, 1968) on the diffusion of pesticide molecules through the polymer membrane. Therefore, the stirring rate was varied during the experimental period. Experimental conditions and results are listed in Table 2. The effluent concentration versus time is shown in Figure 5C. After decreasing the stirring rate, a pronounced delay in attaining a new steady-state concentration was observed. This delay probably reflected the development of a (thicker) gel layer on the polymer surface. It is clear that the effect of the DBL is of major importance for DNOC. In going from a stirring rate of 300 rpm to no mixing, the specific herbicide flux through the emitter membrane decreased by almost a factor of two from 78.6 to 40.4 μg d'1 cm-2. An additional experiment conducted with a stirring rate of 700 rpm resulted in a specific flux of 124.6 μg d"1 cm-2 (data not shown). The results are plotted as specific flux versus stirring rate in Figure 6, where the data points approach a linear regression line (R2 = 0.996). After the conclusion of the experiment, the emitter concentration was measured. The unstirred steady-state concentration was 33.3 mg/L, corresponding to a diffusion coefficient of 1.94x10"7 cm2/s.
Dichlobenil Another stirred flow-through reactor experiment aimed at determining specific flux and diffusion coefficient under laboratory conditions was conducted with solid dichlobenil inside of the emitter. Again, the emitter was cylinder-shaped and in order to minimize the vertical concentration gradient inside of the emitter, the solid dichlobenil was encapsulated in a nylon net fixed along the central axis of the emitter, as
illustrated in Figure 1 B. The experimental conditions and results are summarized in Table 2. The effluent concentration versus time in Figure 7 shows an almost constant steady-state concentration but with a slight concentration decrease over time, most pronounced in the beginning. The explanation is probably the presence of a small fraction of more fine grained and therefore more readily soluble dichlobenil. The transient period lasts for -4 days, and the steady-state flux of dichlobenil through the emitter membrane was 10.23 μg d_1cm-2. After 125 days, the emitter was cut open and the dichlobenil concentration measured. The concentration was 6.95 mg/L, corresponding to a diffusion coefficient of 2.57x10'7 cm2/s.
Laboratory herbicide dissolution experiments
In none of the emitters, saturated herbicide concentrations were obtained (2,4,5-T: 238 mg/L; atrazine: 33mg/L; DNOC: 140 mg/L; dichlobenil: 18 mg/L at 20°C). Therefore, the dissolution rate for the herbicides may become rate limiting for the release of herbicide through the emitter wall. In order to investigate the herbicide dissolution rates at various concentrations, six 100 mL Scott-Durans glass flasks (total volume 138 mL) were filled with millipore water. Two different amounts of each of the herbicides except dichlobenil were encapsulated in 50 μm tube-shaped nylon net.
Each of the six nylon nets were fixed to the plastic cap using a stainless steel hook. After 48 h of preconditioning in millipore water in order to dissolve the most soluble fraction of each herbicide and thereby avoid significant variations in herbicide surface area at the beginning of the experiments, each net was submerged into a flask filled with 130 mL of pure millipore water. No mixing was applied.
When sampling, the herbicide was removed and the solution was stirred for -30 seconds. Then 1-3 mL solution was replaced by millipore water and immediately analysed on a spectrophotometer. The experiments were conducted at room tem- perature ~22°C until the concentration reached the level where the amount of pesticide dissolved over 6 h were approximately equal to the amount removed in 1 mL of sample. Similarly, before closing down the experiments the dissolution rates at 8°C were determined at 5 to 12 different initial concentration for each of the six experiments.
Measured concentrations versus time (A) and dissolved mass pr. L (B) are shown at Figure 8, 9 and 10 for 2,4,5-T, atrazine, and DNOC, respectively. By use of the computer program TableCurve 2D, the concentration data were fitted to a function of the type:
Equation 1: C(t) = (l-[-^~]γ) p + t
where t is time and α, β, and γ are fitting parameters. Similar fits were calculated for the mass of herbicide dissolved per time and volume unit:
Equation 2: m(t) = ι(l-[ ]λ)
where i, K, and λ are the fitting parameters. The dissolution rate is:
^- dm λi , κ α
Equ te (t) = - = — (—
Eliminating t by combination of Equation 1 and 3 yields:
Equation 4: J(C) =
which describes the dissolution rate, J (mg/Lh) at a given concentration, C (mg/L). The calculated fitting parameters are shown in Table 3.
Table 3. Experimental conditions and best-fit fitting parameters for the herbicide dissolution experiments calculated using the computer program TableCurve 2D. The solution volume was 130 L in all the experiments. The herbicide weights are initial weights.
Fitting parameter β γ l K λ
Correlation coeff. R2 R2
Exp. conditions
0.83 g 2,4,5-T, 22°C 290.4 27.78 0.4105 0.9971 843.7 27.06 0.1568 0.9988
1.39 g 2,4,5-T, 22°C 367.3 16.95 0.2729 0.9986 546.1 27.38 0.3068 0.9994
0.57 g atrazine, 22°C 31.59 59.49 3.121 0.9943 53.76 46.86 1.549 0.9974
1.04 g atrazine, 22°Ca 35.87 48.68 2.368 0.9934 61.44 50.16 1.487 0.9969
0.88 g DNOC, 22°C 248.3 27.82 0.3692 0.9961 1238.1 22.59 0.071 0.9982
1.08 g DNOC, 22°C 248.7 16.51 0.2868 0.9972 332.52 26.32 0.3578 0.9982
a This herbicide containing net had been used for 6 months in an emitter experiment prior to the dissolution experiments.
It can be seen from Figure 8 - 10 that the function provides a good fit of the experimental data. The differences between the concentration curves at a given temperature are much less than should be expected if the dissolution rate was proportional to the herbicide surface area (i.e. the weight of the herbicide). This is particularly evident from the DNOC data (Figure 11 ). Therefore, diffusion of herbicide from the surface of the solid matrix and into solution must be the main controlling factor for the dissolution rate, in particular at high concentrations where the diffusion is slow because of the small concentration gradient. This is evident from the fact that the two sets of curves are almost parallel at high concentrations, which indicates that small variations in sizes and weights of the herbicide containing nylon nets inside of a diffusive emitter are unlikely to have a significant effect on the resulting mass flux.
In the experiments with dissolution of atrazine, the large herbicide containing net had been used in an emitter experiment for -6 months before use. This is reflected in the initial dissolution rates (at 22°C) which are highest for the low weight atrazine. However, during the experiment the dissolution rate for the high weight atrazine overtakes. This demonstrates that in experiments with emitters containing solid phase herbicide, the herbicide solubility decreases over time due to dissolution of the most soluble material. Nevertheless, the results also indicate that this decrease may be of minor importance, especially at high concentrations, and only during the first few days of an experiment.
Dissolution rates for the herbicides at 8°C were determined at a number of concentrations. Plots of measured rates at 8°C versus calculated rates for 22°C (Equation 4) are shown at Figures 9 - 11 , (C) and (D). It can be seen that linear fits provide a reasonable approximation, particularly for the 2,4,5-T dissolution data, providing a means for estimation of dissolution rates at 8°C. The equations for the linear fits and the correlation coefficients are shown at the figures.
Plots of J(C) at 22°C versus concentration for the largest solid matrix of each of the three herbicides, calculated from Equation 4, are shown in Figure 12. It is interest- ing to note that the plot for the neutral atrazine is a straight line, i.e. the dissolution rate depends on the aqueous concentration only. For the acidic herbicides 2,4,5-T and DNOC, the dissolution rate also depends on the pH of the solution.
The possibility of calculating the dissolution rate as a function of concentration is providing a means of estimating the emitter herbicide concentration when the total flux through the emitter membrane is known.
Example 2
Field experiments
Three field experiments aimed at evaluating the degradation of the herbicides 2,4,5- T, atrazine, and DNOC, and one field experiment aimed at evaluating the sorption of dichlobenil in the test aquifer were carried out. The experiments were conducted at 3-4 mbs (meters below surface) in a shallow, anaerobic sand aquifer located in Tisvilde Hegn, Northern Zealand, Denmark. The upper -2 m consists of aeolian sand followed by Post-Glacial marine sand deposits. At 8.75-9.25 mbs the sand aq- uifer is bounded by clayey till. The water table is generally 1.5-2.0 mbs, fluctuating approximately 0.5 m over the year. The gradient is approximately ten (10) per thousand (o/oo) and virtually unaffected by the fluctuating groundwater table, resulting in an average groundwater velocity at 3-4 mbs of -100 m/yr determined from breakthrough curves for tritiated water (Arildskov, unpublished data). The dominant redox processes are iron- and sulfate reduction from 3-3.5 mbs and sulfate reduction from 3.5-4 mbs (Arildskov et al., submitted).
The diffusive emitters were installed in a row, Fence A, approximately perpendicular to the groundwater flow direction, consisting of 10 adjacent 2 inch (5.08 cm) inner diameter source wells with the screens located from 3-4 mbs. To remove possible flow obstructions by the well screens, the wells were dry-pumped several times before their use. After experiencing clogging of the well screens due to precipitation of iron (hydr)oxides, the well pipes were flushed with nitrogen and sealed with butyl rubber stoppers after submerging the emitters.
Five source wells (total width -0.3 m) were used in each experiment (Figure 11A). The field emitters contained both solid herbicide and tritiated water (tracer). Close- ups of the emitters are shown in Figure 11 B, and relevant data can be found in Table 4.
Table 4. Data for diffusive emitters installed in the source wells with calculated specific fluxes and diffusion coefficients for the field experiments. The aquifer porosity is estimated to be 0.325, the groundwater flow velocity is -100 m/yr, the plume cross sectional area is ~0.5 m2, and the polymer thickness, / = 75 μm. The total length of one emitter is 1 m.
Parameter Unit 2,4,5-T Atrazine DNOC Dichlobenil
Emitter cell volume mL 16 130 165 130
Number of emitter cells m-1 22 5 4 5
Total emitter surface area cm2/ 880 900 900 900 m
Amount of solid herbicide g/L 20 50 40 35
Source well herbicide min. μg/L 183.4 32.95 1451 222.5Θ concentration3 max. μg/L 323.2 67.58 1625
Specific flux min. μg d'1 1.56 0.27 11.96 1.84e max. cm'2 2.73 0.56 13.40
Emitter concentration mg/L 175b 30b 50.1c 7b
Diffusion coefficient min. cm2/s 7.7x10'10 7.8x10'10 2.1 x10'8 2.3x10'8 max. cm2/s 1.4x10'9 1.6x10'9 2.3x10'8
Source well HTO min. μg/L 18.3 15.5 13.0 18.3e concentration3 max. μg/L 25.1 20.7 23.7
Specific flux min. μg d'1 0.15- 0.13 0.11 0.15 max. cm"2 0.21 0.17 0.20
HTO emitter concentrationd mg/L 566 500 500 500
Diffusion coefficient min. cm2/s 2.4χ10'11 2.2x10'11 1.9x10'11 2.6x10'11 e max. cm2/s 3.2x10'11 3.0x10'11 3.4x10'11 a Average for the five source wells Estimated c Measured; average for 20 emitter bags d Initial concentration
6 Average for day 3 to day 68
Samples from the source wells were collected through teflon tubing with a filter installed close to the well screen at 3.5 mbs (2,4,5-T and atrazine), from three filters installed close to the downgradient end of the well screen at 3.25, 3.5 and 3.75 mbs (DNOC), or from four filters installed close to the downgradient end of the well screen at 3.2, 3.4, 3.6 and 3.8 mbs (dichlobenil). Multilevel samplers with sampling points at 3.2, 3.4, 3.6, and 3.8 mbs (Figure 11 A) were installed during the experiments at horizontal distances 0.2, 0.4, 0.6, 1.0, 1.5, 3.0, 5.0 and 10.0 m downgradient of Fence A. All samples were collected using a 10 mL polypropylene (PP) syringe (B-D® Plastipak, Becton Dickinson) fitted with a three-way valve. To remove residual water from the PTFE tubing, the first mL was discarded, after which 5 mL of sample was collected and filtered through a 0.2 μm PTFE-filter (Advantec/MFS 13HP). This filter was chosen because of its weak sorption of a number of pesticides (Clausen, 2000). When sampling, the first 2 mL was discarded, and the following 2 mL was filtered into a 20 mL PE vial for scintillation counting. Finally, the remaining 1 mL was filtered into 2 mL glass HPLC-vials sealed with 8 mm Tef- lon/silicone SEPTA (National Scientific Company, part no. C4013-60), and filled with oxygen-free N2 to prevent precipitation of iron(hydr)oxides in the vials. To remove organic impurities, HPLC-vials were heated to 550°C for 24 h before use.
2,4,5-T/HTO
In the first field experiment, 2,4,5-T and HTO were released simultaneously to the aquifer during a 241 day period. The average (C2A5.T/ CHTO)-ratios for the source wells and downgradient multilevel samplers (representing various residence times) at day 145 and day 241 are shown in Figure 12. During the earlier stages of the ex- periment clogging of the well screens caused by precipitation of iron (hydr)oxide was experienced. However, after clean-pumping, the well pipes were sealed at the surface with rubber stoppers to minimise oxygen intrusion, which significantly reduced the problem. At both sampling days, the ratios were constant from the source wells down to samplers located 1.5 m downgradient, corresponding to a travel time of 5-6 days. Therefore, no detectable degradation occurred within this period of time. However, at the border of the plume, the ratios were lower than in the centre. This is likely due to the different diffusion coefficients in water for 2,4,5-T (-3.7x10'7 cm2/s for 2,4,5-T at 8°C), and HTO (1.35χ10'5 cm 2/s at 8°C,) (Arildskov, 2000)
causing a difference in the transversal diffusive spreading of -3 cm after 6 days of travel time.
Calculated specific fluxes and diffusion coefficients for day 145 and 241 are shown in Table 4. Between day 145 and 241 , the 2,4,5-T concentrations had increased by a factor of 2, whereas the HTO concentrations increased by a factor of 1.5. A likely explanation for the general increase is that small amounts of oxygen have been able to diffuse through the well casing or the rubber stoppers, causing some extend of clogging of the well screens with iron oxides, and therefore a decrease in groundwater flow rate, to occur. The smaller increase for HTO may be caused by HTO-exhaustion due to the long experimental period.
Atrazine /HTO
In the second field experiment, atrazine and HTO were released to the aquifer dur- ing a 200 day period. The average (Catrazine/ CHTO)-ratios versus residence time for the source wells and downgradient multilevel samplers are shown in Figure 13. At day 21 , the ratios for both the source wells and the multilevel samplers were close to 2, and the obvious conclusion was that little or no degradation occurred during the -9 days of travel time. A late sampling round (day 200) led to the same conclu- sion, although the (Catrazine/ CHTO)-ratios had increased to 4-5. In order to investigate the consistency of the emitters over time, samples were collected from the source wells and selected downgradient piezometers (located in the centre of the plume) at regular intervals for the first 110 days of the experiment. The results are shown as (Cat azine/ CHTO)-ratios versus time in Figure 14. Initially, elevated atrazine concentra- tions, probably caused by saturation inside of the emitter bags when submerged into the source wells, were evident. In this experiment care was taken to minimize the intrusion of oxygen from the beginning, resulting in stable ratios around 2-3 for more than 100 days. However, in agreement with the results discussed above, there was no sign of degradation, i.e. the ratios did not decrease with increasing distance from the source wells. Calculated specific fluxes and diffusion coefficients for day 21 and 200 are shown in Table 4. Again, the herbicide concentration had increased more over time than the HTO concentration; probably for the same reasons as discussed above. Iron oxide precipitates may well have affected the flow through the well screens significantly, since they were clearly visible on the upper part of the
emitters when they were recovered from the source wells. At day 200, one source well appeared to be completely clogged because of huge concentrations of both atrazine (-18 mg/L) and HTO (-9.5 mg/L), and was therefore excluded from the data set.
DNOC /HTO
Three months after completion of the 2,4,5-T experiment, new emitters containing HTO and solid DNOC were installed in the same source wells for a 192 day period. The average (Cmocl CHTO)-ratios for source wells and downgradient multilevel sam- piers at day 25 and 192 are shown in Figure 15. At day 25, the ratios decreased rapidly from -100 in the source wells to below the detection limit (10 μg/L) in multilevel samplers located 0.6 m and further downgradient of the source wells. At day 192, DNOC could be detected 1.5 m downgradient. Clearly, the DNOC was degraded within the aquifer. For all five sampling dates, the degradation followed first- order kinetics with respect to the DNOC concentration (Table 5). However, the rate decreased with time from onset of the experiment (Table 5). This phenomenon is discussed in detail elsewhere (Arildskov et al., submitted).
Table 5. Field derived first-order DNOC degradation rate constants and linear correlation coefficients for -ln(r/r0) (r=[CDNOC / CHTO]-ratio) versus time at different sampling days.
Time from onset of k R2 Number of experiment (d) (d'1) data points
25 1.47 0.98 3
57 0.74 0.97 5
84 0.51 1.00 5
148 0.37 0.96 6
192 0.35 0.97 6
Calculated specific fluxes and diffusion coefficients for day 25 and 192 are shown in Table 4. In contrast to previous results, the source well ratios declined (-30%) with time, even though the tracer concentration increased by 80% during the same 167 days. Therefore, significant clogging has likely occurred, but in the case of DNOC,
iron oxide precipitation inside the well screens may have caused considerable iron oxide mediated degradation of the herbicide even before it left the source wells (cf. Arildskov et al., submitted).
Dichlobenil/HTO
Three months after completion of the DNOC experiment, new emitters containing HTO and solid dichlobenil were installed in the same source wells for a 68 day period. In this case the investigation focussed on sorption of the compound to the aquifer sediment, and therefore break-through curves for dichlobenil and HTO for mul- tilevel samplers at various downgradient distances from the source wells (corresponding to various travel times in the aquifer) were compared. In order to minimise the transient phase, during which the solute break through the polymer, the field emitters were preconditioned in water for 7 days prior to installation. Figure 16 shows measured and calculated average concentrations in the source wells. It can be seen that the steady-state concentrations are fairly stable for both dichlobenil and HTO. The time required to reach steady-state in the source wells is only 1-2 days. The break-through for tritiated water clearly occurs before the break-through for dichlobenil (Figure 17). Field retardation factors were calculated from the time difference for the 50% break-through for the two compounds. The field measured retardation factors were in the range 1.36 to 1.60 for downgradient distances 1.5 to
10 meters, slightly higher in 5 and 10 m than in 1.5 and 3 m. This could be due to small variations in the sediment organic matter content.
Conclusions It was demonstrated that the passive diffusive emitters containing excess solid herbicide were able to release stable concentrations of 2,4,5-T, atrazine, DNOC, and dichlobenil for several months in the laboratory after a transient period of a few days duration. Herbicide dissolution experiments could be used to predict the emitter concentration, but the actual release rate was determined by both the dissolution rate and the diffusion coefficient of the herbicide in the polymer. The field emitters containing both herbicide and HTO released both compounds for up to 8 months. In the field, the released concentrations varied more than in the laboratory experiments which could be contributed to natural variations in the groundwater flow and clogging of the well screens.
The field derived diffusion coefficients were lower than laboratory values. For HTO, the difference corresponded to a factor of 2-3 which could be explained by differences in temperature and mixing rate. For the herbicides, the field derived values were in general a factor of 10 lower than in the laboratory. This could only be partly explained by differences in temperature and mixing rate. However, the same observation was done by Arildskov and Devlin (2000) who released PCE through nylon tubing to another aquifer. Therefore, the deviations seems larger for low polarity molecules and not aquifer specific. Nevertheless, if the difference is taken into ac- count, laboratory derived diffusion coefficients can be used to design field release system that would suit most practical applications.
The herbicide to tritiated water ratios in downgradient multilevel samplers were stable for the herbicides 2,4,5-T and atrazine, which were not degraded in the test aq- uifer within a residence time of -6 days. The system was consistent enough to demonstrate first-order degradation of DNOC without the detection of degradation products. Furthermore, sorption of dichlobenil in the aquifer could be measured by comparison of break-through curves for the herbicide and tritiated water, providing a means for calculating the retardation factor. In summary, both abiotic degradation and sorption have been detected by use of the passive diffusive emitters.
Claims
1. Emitter cell comprising
i) a compartment comprising a fluid composition comprising at least one of a) an assayable compound, and b) a tracer moiety, or a combination of both,
ii) wherein said composition comprised in said compartment is separated from a predetermined environment by at least one selectively permeable membrane capable of bringing at least one of said a) and b), when present, or a combination of both, into contact with said predetermined environment, and
iii) wherein, when a) is present, at least one of said a) and b) is brought into contact with said predetermined environment by means of passive diffusion.
2. Emitter cell according to claim 1 , wherein a) is brought into contact with said en- vironment by means of passive diffusion in the absence of b).
3. Emitter cell according to claim 1 , wherein a) is brought into contact with said environment by means of passive diffusion and b) is brought into contact with said environment by means of semi-passive diffusion.
4. Emitter cell according to claim 1 , wherein a) is brought into contact with said environment by means of semi-passive diffusion and b) is brought into contact with said environment by means of passive diffusion.
5. Emitter cell according to claim 1 , wherein a) is brought into contact with said environment by means of passive diffusion and b) is brought into contact with said environment by means of passive diffusion.
6. Emitter cell according to claim 1 , wherein b) is brought into contact with said environment by means of passive diffusion in the absence of a).
7. Emitter cell according to claim 1 , wherein b) is brought into contact with said en- vironment by means of semi-passive diffusion in the absence of a).
8. Emitter cell according to any of the preceding claims, wherein said composition comprises at least one further assayable compound or a detectable substance operably linked to at least one of said assayable compound and said further as- sayable compound.
9. Emitter cell according to claim 8, wherein said assayable compound and/or said further assayable compound is selected independently from the group consisting of chemical compounds and the group consisting of biological compounds.
10. Emitter cell according to claim 9, wherein said biological compound is a microbial cell selected from the group consisting of eukaryotic microbial cells and pro- karyotic microbial cells.
11. Emitter cell according to claim 9, wherein said chemical compound is a pesticide.
12. Emitter cell according to claim 11 , wherein said pesticide is selected from the group consisting of a herbicide, an insecticide and a fungicide.
13. Emitter cell according to claim 9, wherein said assayable compound and/or said further assayable compound, when present in water, is a potential health hazard and/or generally undesirable for human and/or animal consumption.
14. Emitter cell according to claim 1, wherein said tracer moiety comprises a detectable label.
15. Emitter cell according to claim 14, wherein said detectable label comprises a radiolabel and/or a fluorescently detectable label.
16. Emitter cell according to claim 15, wherein said tracer moiety comprises a radiolabel.
17. Emitter cell according to claim 16, wherein said tracer moiety comprises tritiated water.
18. Emitter cell according to claim 14, wherein one or more of said assayable compound and said further assayable compound and said tracer moiety is reversibly bound to a solid phase.
19. Emitter cell according to claim 18, wherein said solid phase comprises a silica gel or a resin.
20. Emitter cell according to claim 18, wherein said tracer moiety is reversibly bound to a solid phase.
21. Emitter cell according to claim 20, wherein said solid phase comprises a silica gel.
22. Emitter cell according to any of the preceding claims, wherein said fluid comprises a liquid.
23. Emitter cell according to claim 22, wherein said liquid comprises an aqueous solvent.
24. Emitter cell according to any of the preceding claims, wherein said composition comprises a plurality of different assayable compounds.
25. Emitter cell according to claim 24, wherein said composition comprises from two to ten different assayable compounds.
26. Emitter cell according to any of claims 14 to 25, wherein said composition comprises at least one further tracer moiety.
27. Emitter cell according to claim 26, wherein said composition comprises from two to five different tracer moieties.
28. Emitter cell according to claim 27, wherein said composition comprises three or four different tracer moieties.
29. Emitter cell according to any of the preceding claims, wherein said selectively permeable membrane comprises a polymer.
30. Emitter cell according to claim 29, wherein said polymer is substantially impermeable to charged particles including ionic species.
31. Emitter cell according to any of the preceding claims comprising at least one further selectively permeable membrane.
32. Emitter cell according to claim 31 , wherein said selectively permeable membrane and said at least one further selectively permeable membrane have essentially identical permeability properties.
33. Emitter cell according to claim 32, wherein the permeability of said selectively permeable membrane is different from the permeability of at least one of said at least one further selectively permeable membrane.
34. Emitter cell according to any of the preceding claims, wherein essentially the same amount of assayable compound is released per time unit under practical circumstances.
35. Emitter cell according to any of the preceding claims, wherein the ratio between i) the amount of tracer moiety released per time unit, and ii) the amount of assayable compound released per time unit, are essentially the same under practical circumstances.
36. Emitter cell according to any of the preceding claims, wherein said predetermined environment is selected from the group consisting of a soil, a sediment of an agricultural field, and a groundwater reservoir.
37. Emitter cell according to any of the preceding claims, wherein the amount of tracer is at least 1 mg/litre and preferably less than 10000 mg/litre.
38. Emitter cell according to any of the preceding claims, wherein the amount of assayable compound is at least 0.01 g/litre and preferably less than 1000 g/litre.
39. Emitter cell according to any of the preceding claims, wherein the relative change in the concentration of the assayable compound in the cell is less than 20 percent per 48 hours.
40. Emitter cell according to any of the preceding claims, wherein said permeable membrane has a diffusion coefficient for transport through said permeable membrane of said assayable compound or said tracer, said diffusion coefficient being in the range of from 10"13 to 10"6 cm/Vsek.
41. Emitter cell according to any of the preceding claims, wherein said assayable compound is contacted by a fluid permeable matrix capable of releasing said assayable compound into said fluid composition.
42. Emitter cell according to claim 41 , wherein the mesh size of said fluid perme- able matrix is at least 1 μm and preferably less than 100 μm.
43. Device comprising a plurality of operably linked emitter cells according to any of claims 1 to 42.
44. Device according to claim 43, wherein each emitter cell comprises a different assayable compound and/or a different tracer moiety.
45. Kit comprising the emitter cell according to any of claims 1 to 42 and/or the device according to any of claims 43 and 44, in combination with detection means for detecting at one or more of said assayable compound and said operably linked detectable substance and said tracer moiety and said further tracer moiety.
46. Method for monitoring at least one assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of:
i) providing at least one assayable compound and/or an operably linked detectable substance,
ii) providing an emitter cell according to any of claims 1 to 42 or the device according to any of claims 43 and 44,
iii) providing a predetermined environment in which the assayable compound and/or an operably linked detectable substance can be monitored over time,
iv) providing means for detecting said assayable compound and/or an operably linked detectable substance,
v) introducing said assayable compound and/or an operably linked detectable substance into a compartment of said emitter cell,
vi) introducing said emitter cell comprising said assayable compound and/or an operably linked detectable substance into said predetermined environment,
vii) releasing said assayable compound and/or an operably linked detectable substance comprised in said emitter cell into said environment under controllable conditions, and
viii) monitoring said assayable compound and/or an operably linked detectable substance in said predetermined environment by means of said detection means.
47. Method for monitoring at least one assayable compound and/or an operably linked detectable substance in a predetermined compartment, said method comprising the steps of:
i) providing at least one assayable compound and/or an operably linked detectable substance,
ii) providing an emitter cell according to any of claims 1 to 42 or the device according to any of claims 43 and 44,
iii) providing a predetermined compartment in which the assayable compound and/or an operably linked detectable substance can be monitored over time,
iv) providing means for detecting said assayable compound and/or an operably linked detectable substance,
v) introducing said assayable compound and/or an operably linked detectable substance into said predetermined compartment of said emitter cell or a further compartment of said device,
vi) introducing said emitter cell comprising said assayable compound and/or an operably linked detectable substance into a predetermined environment,
vii) bringing said assayable compound and/or an operably linked detectable substance comprised in said emitter cell into contact with said predetermined environment under controllable conditions, and
viii) monitoring said assayable compound and/or an operably linked detectable substance in said predetermined compartment by means of said detection means.
48. Method for monitoring the sorption of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method of claim 46 and at least a further step of monitoring the sorption of said assayable compound and/or said operably linked detectable substance in said predetermined environment.
49. Method for monitoring the biotic degradation of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method of claim 46 and at least a further step of monitoring the biotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined environment.
50. Method for monitoring the biotic degradation of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method of claim 47 and at least a further step of monitoring the biotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined compartment.
51. Method for monitoring the abiotic degradation of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method of claim 46 and at least a further step of monitoring the abiotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined environment.
52. Method for monitoring the abiotic degradation of an assayable compound and/or an operably linked detectable substance in a predetermined environ- ment, said method comprising the steps of the method of claim 47 and at least a further step of monitoring the abiotic degradation of said assayable compound and/or said operably linked detectable substance in said predetermined compartment.
53. Method for monitoring the stability of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method of claim 46 and at least a further step of monitoring the stability of said assayable compound and/or an operably linked detectable substance in said predetermined environment.
54. Method for monitoring the stability of an assayable compound and/or an operably linked detectable substance in a predetermined environment, said method comprising the steps of the method of claim 47 and at least a further step of monitoring the stability of said assayable compound and/or an operably linked detectable substance in said predetermined compartment.
55. Method for monitoring at least one tracer moiety in a predetermined environment, said method comprising the steps of:
i) providing at least one tracer moiety,
ii) providing an emitter cell according to any of claims 1 to 42 or the device according to any of claims 43 and 44,
iii) providing a predetermined environment in which the tracer moiety can be monitored over time,
iv) providing means for detecting said tracer moiety,
v) introducing said tracer moiety into said emitter cell,
vi) introducing said emitter cell comprising said tracer moiety into said predetermined environment,
vii) releasing said tracer moiety comprised in said emitter cell into said environment under controllable conditions, and
viii) monitoring said tracer moiety in said predetermined environment by means of said detection means.
56. Method for determining the flow of a tracer moiety in an environment, said method comprising the steps of the method of claim 55 and at least a further step of determining the flow of said tracer moiety in said predetermined environment.
57. Method for monitoring at least one assayable compound and/or an operably linked detectable substance in a predetermined compartment, said method comprising the steps of:
i) providing at least one tracer moiety,
ii) providing an emitter cell according to any of claims 1 to 42 or the device according to any of claims 43 and 44,
iii) providing a predetermined environment in which the tracer moiety can be monitored over time,
iv) providing means for detecting said tracer moiety,
v) introducing said tracer moiety into said emitter cell,
vi) introducing said emitter cell comprising said tracer moiety into said predetermined environment,
vii) releasing said tracer moiety comprised in said emitter cell into said environment under controllable conditions, and
viii) monitoring said tracer moiety in said predetermined environment by means of said detection means,
ix) determining the flow of said tracer moiety in said predetermined environment,
x) providing at least one assayable compound and/or an operably linked detectable substance, xi) providing an emitter cell according to any of claims 1 to 42 or the device according to any of claims 43 and 44,
xii) providing a predetermined environment or a predetermined compartment in which the assayable compound and/or an operably linked detectable substance can be monitored over time,
xiii) providing means for detecting said assayable compound and/or an operably linked detectable substance,
xiv) introducing said assayable compound and/or an operably linked detectable substance into said predetermined compartment of said emitter cell or a further compartment of said device,
xv) introducing said emitter cell comprising said assayable compound and/or an operably linked detectable substance into a predetermined environment,
xvi) bringing said assayable compound and/or an operably linked detectable substance comprised in said emitter cell into contact with said predetermined environment under controllable conditions, and
xvii) monitoring said assayable compound and/or an operably linked detectable substance in said predetermined environment or predetermined compartment by means of said detection means.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2001234026A AU2001234026A1 (en) | 2000-03-06 | 2001-03-05 | Device and method for bringing a compound into contact with an environment |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DKPA200000360 | 2000-03-06 | ||
| DKPA200000360 | 2000-03-06 | ||
| US24372500P | 2000-10-30 | 2000-10-30 | |
| US60/243,725 | 2000-10-30 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| WO2001067094A2 true WO2001067094A2 (en) | 2001-09-13 |
| WO2001067094A3 WO2001067094A3 (en) | 2002-01-17 |
Family
ID=26068784
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/IB2001/000307 WO2001067094A2 (en) | 2000-03-06 | 2001-03-05 | Device and method for bringing a compound into contact with an environment |
Country Status (2)
| Country | Link |
|---|---|
| AU (1) | AU2001234026A1 (en) |
| WO (1) | WO2001067094A2 (en) |
Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DD110350A1 (en) * | 1974-01-25 | 1974-12-12 | ||
| US4505889A (en) * | 1982-09-23 | 1985-03-19 | Rohm And Haas Company | Protracted release microbiocidal article for aqueous systems |
| EP0325492A1 (en) * | 1988-01-22 | 1989-07-26 | Bend Research, Inc. | Osmotic system for delivery of dilute solutions |
| EP0511853A2 (en) * | 1991-05-01 | 1992-11-04 | Reckitt And Colman Products Limited | Apparatus for emitting a chemical agent |
| US5702684A (en) * | 1994-05-02 | 1997-12-30 | Nalco Chemical Company | Method of use of compositions of biocides and fluorescent indicators to control microbial growth |
| WO1998037959A2 (en) * | 1997-02-24 | 1998-09-03 | Willuweit, Thomas | Device for the metered dispensing of substances |
| US5807697A (en) * | 1996-04-19 | 1998-09-15 | Lockheed Martin Energy Systems, Inc. | Biological tracer method |
| US5902749A (en) * | 1997-09-18 | 1999-05-11 | The United States Of America As Represented By The Secretary Of The Interior | Automated chemical metering system and method |
-
2001
- 2001-03-05 AU AU2001234026A patent/AU2001234026A1/en not_active Abandoned
- 2001-03-05 WO PCT/IB2001/000307 patent/WO2001067094A2/en active Application Filing
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DD110350A1 (en) * | 1974-01-25 | 1974-12-12 | ||
| US4505889A (en) * | 1982-09-23 | 1985-03-19 | Rohm And Haas Company | Protracted release microbiocidal article for aqueous systems |
| EP0325492A1 (en) * | 1988-01-22 | 1989-07-26 | Bend Research, Inc. | Osmotic system for delivery of dilute solutions |
| EP0511853A2 (en) * | 1991-05-01 | 1992-11-04 | Reckitt And Colman Products Limited | Apparatus for emitting a chemical agent |
| US5702684A (en) * | 1994-05-02 | 1997-12-30 | Nalco Chemical Company | Method of use of compositions of biocides and fluorescent indicators to control microbial growth |
| US5807697A (en) * | 1996-04-19 | 1998-09-15 | Lockheed Martin Energy Systems, Inc. | Biological tracer method |
| WO1998037959A2 (en) * | 1997-02-24 | 1998-09-03 | Willuweit, Thomas | Device for the metered dispensing of substances |
| US5902749A (en) * | 1997-09-18 | 1999-05-11 | The United States Of America As Represented By The Secretary Of The Interior | Automated chemical metering system and method |
Non-Patent Citations (2)
| Title |
|---|
| DATABASE COMPENDEX [Online] Engineering Information Inc., USA; AN EIX98244170983, 1998 ANTON, S.D., ET AL.: "Subsurface herbicide application with the John Deere MulchMaster" XP002157411 * |
| MALOSZEWSKI P ET AL: "TRANSPORT PARAMETERS OF SOME HERBICIDES DETERMINED FROM A TRACER TEST" IAHS-AISH PUBLICATION,INTERNATIONAL ASSOCIATION OF HYDROLOGICAL SCIENCES,,SL, no. 250, 1998, pages 529-535, XP000980330 ISSN: 0144-7815 * |
Also Published As
| Publication number | Publication date |
|---|---|
| AU2001234026A1 (en) | 2001-09-17 |
| WO2001067094A3 (en) | 2002-01-17 |
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