GB2024016A - Degradation of pesticide residues - Google Patents

Abstract

Pesticide, e.g. herbicide or insecticide, residues are degraded in situ by application to the locus of the residue of an active oxygen- releasing compound. Potassium oxy- sulphate salts are particularly useful in neutralizing the phytotoxic activity of triazine herbicide residue, and the use of percarbonates is also disclosed.

Description

SPECIFICATION Degradation of pesticide residues THIS INVENTION relates to degradation of pesticide residues, and concerns methods for degrading pesticide, for example herbicide or insectiside residues remaining at a locus, e.g., in soil and/or plants, which has previously been treated with the pesticide and also concerns compositions for use in such methods.

For a number of years, triazine herbicides have been economically very important class of herbicide, expecially in the agriculture industry. These herbicides have application in controlling a broad spectrum of weeds and other undesirable vegetation. On certain valuable crops, such as corn, milo and sorghum, such herbicides have a somewhat limited phytotoxic effect, which makes them particularly valuable for use in association with those crops. Particularly well-known triazine herbicides include 2-chloro-4-ethylamino-6-ispropylamine-s-triazine, 2-chloro-4,6-bis (ethylamino)-s-triazine, 2(4-chloro-6-ethyla mi no-s-triaz ine-2-yl-amino)-2-methylpropionitrile, 2-chloro4-cyclopropylamino-6-isopropylamine-s-triazine, and combinations thereof.The most popular triazine herbicides are currently marketed under several trade names, including Atrazine, Aatrex, Bladex, Evik, Lexone, Princep Sencor, Simazine, Metribuzin, Ametryn, Prometryne, Propazine, Procyazine, and Terbutryn. A more complete description of the activity of the triazine herbicides is contained in Pamphlet 738, issued by the Cooperative Extension Service of lowa State University in April of 1977.

The herbicide is typically distributed uniformly over the field to be treated, being incorporated by any acceptable procedure into the top two to three inches (5 to 7.5 cm) of the soil.

Unfortunately, the triazines exhibit an undesirable residual phytotoxic activity which degrades very slowly, sometimes taking up to several years. Further, it has been found that, unlike corn, milo and sorghum, most other desirable crops are affected adversely by the toxic activity of triazines, some at a concentration level as low as 0.02 ppm. As a result, the triazines are rarely used where crop rotations or multiple crop plantings are necessary or desirable. Moreover, where a crop, such as corn, planted in a field selectively treated with a triazine herbicide, is destroyed or damaged before harvest, as by hail, it is usually not possible for a quicker maturing crop, such as soybeans, sunflowers or the like to be successfully planted in the same field in place of the original crop because of the toxic activity of the herbicide residue.

In view of the obviously desirable advantages of triazine herbicides, many attempts have been made previously to develop techniques for degrading or safening these herbicides in order to permit their use with otherwise sensitive crops. Safening agents which have been proposed have not been commercialized because of their high cost and because some have produced undesirable byproducts in the reaction with the herbicide. Thus, procedures which could be employed selectively to inhibit or degrade the phytotoxic activity of triazine herbicide residues without producing any undesirable byproducts or adversely affecting the environment would be of exceptional value in extending the utility of these herbicides. Other pesticides, such as insecticides, have similarly had their utility diminished or essentially destroyed as a result of their adverse residual effects on the environment.For example, certain chlorinated aromatic hydrocarbons, which do not decompose naturally, have been found to be concentrated by storage in the fatty tissue of certain plants and animals. Extensive efforts have been made to develop commercially and environmentally effective procedures to break down these compounds or otherwise inhibit the toxic effects which follow their otherwise desirable usage in killing pests. As of this time, many insecticides have had to be removed from the market because no acceptable safening procedures have been developed.

The present invention is concerned with a method for degrading residual organic chemical pesticides, such as herbicides and insecticides, in situ, i.e. remaining at the locus of their previous use, whereby residual harmful or potentially harmful chracteristics are substantially reduced with no adverse environmental effect.

In one aspect the present invention provides a method for degrading an organic chemical pesticide remaining as a residue at the locus of previous use of such pesticide, which method comprises treating the locus, by a suitable agronomic application technique, with an active oxygen-releasing compound which does not adversely affect the environment at said locus in a manner such that an effective amount of active oxygen is release at said locus to contact said chemical pesticide residue.

Thus in the method of the present invention, a pesticide residue is degraded by treating the location where the residue is present by use of a composition comprising an active oxygen-releasing compound which, through reaction of the active oxygen with the chemical residue, degrades and neutralizes the toxic activity of the chemical without leaving any harmful residue or byproduct in the soil.

It is found that, for example, the relatively stable potassium oxysulphate and peroxysulphate salts possess the desirable characteristic of having no adverse environmental impact on the fields to be treated and these compounds thus constitute preferred active oxygen-releas ing component for use in the invention. More importantly, these salts function to release active oxygen in such a manner that only extremely low levels of salt application are necessary to degrade effectively the toxic activity of the pesticide residue.

In a preferred method of the present invention, soil at the locus to be treated is assayed to obtain a quantitative determination of the pesticide content and possibly also an indication of the overall pH of the environment. The composition containing the oxygen-releasing compound, e.g. potassium oxysulphate salt, is then applied to the locus in appropriate preferred quantities or preferred form, as dis cussed below, by any agronomically acceptable technique which results in contact between the active oxygen which is released and the chemical pesticide residue.

The oxygen-releasing compound may be applied to the growth medium at the locus of the crop or directly to the plants themselves.

Within a time period of from 36 to 72 hours, the toxic activity of the chemical pesticide will be observed to degrade to an acceptable level.

Under many circumstances, the active oxygen-releasing compound, e.g. sulphate salts, may be applied alone, without any additive or diluent. More often, however, it will be preferred to apply the active component of the present invention in an agricultural composition or formulation which also includes an agronomically acceptable carrier. It may also be desirable to add a small amount, typically less than about 5 parts by weight, of buffering agent, e.g. sodium bicarbonate or sodium sulphate, to adjust the stability of the active oxygen-releasing compound to take into account the pH of the environment of application. Such compositions may also be mixed with fertilizers or fertilizer materials before their application, provided the fertilizer composition is not one which adversely reacts with the active oxygen-releasing component of the composition.

By "agronomically acceptable carrier" is meant any substance which can be used to dissolve, disperse, or diffuse a compound in the composition without impairing the effectiveness of the compound and which by itself has no detrimental effect on the soil, equipment, crops, or agronomic environment. Thus, it will be apparent to those skilled in the art that the compositions to be used in the methods of the present invention may be applied either in solid formulations which may thereafter be wetted into the soil or may be applied directly in liquid form, e.g. in solution.

In post-emergence applications, it will usually be desirable to include one or more adjuvants, such as wetting agents, surfactants, spreading agents, and the like, for enhancing the ability of the composition to adhere to, and be absorbed into, the plant.

In its particularly preferred form, the method of the present invention may be used for substantially neutralizing the herbicidal activity of triazine herbicide residue at the locus of a previous agronomic application of the herbicide such that crops to which the herbicide is phytotoxic may be successfully planted at and harvested from said locus.

Hence in a further aspect, the present invention provides a method for substantially reducing the herbicidal activity of a triazine herbicide residue at the locus of a previous application of said herbicide, which method comprises treating said locus, by means of any suitable agronomic application technique, with an environmentally safe active oxygenreleasing compound which releases active oxygen subsequent to its application at said locus.

According to this aspect of the invention, the locus of the triazine herbicide residue is treated in an agronomically suitable manner with a composition containing an effective amount of an active oxygen-releasing compound, e.g. potassium peroxysulphate salt, which is relatively stable at the pH of the locus of application and which will release active oxygen in the presence of water.

The locus is preferably so treated that the triazine herbicide is contacted by the active oxygen-releasing compound, e.g. salt at a mole ratio greater than about 0.5 to 1 moles and less than about 5 moles of salt per more of triazine herbicide. For most triazine herbicides the preferred contact ratio will be between about 1:1 and about 4:1, with the ratio of about 2 moles salt per mole of triazine being particularly advantageous.

As used herein, "herbicidal activity" refers to that characteristic property of a compound which results in the control or modifying of the natural growth of vegetation or plants.

Such controlling or modifying effects include all deviations from natural development such as, for example, killing, retardation, defoliation, desiccation, regulation, stunting, tillering, stimulation, dwarfing, and the like.

Unless otherwise indicated herein, the term "plants" will be intended to include germinant seeds, as well as emerging seedlings and established vegetation, and will include also both below- and above-ground portions.

The triazine herbicides which may be substantially neutralized by practice of the present invention are active herbicides of a general type, typically effective against a wide range of plant species with essentially no discrimination between desirable and undesirable species. These herbicides may be characterized chemically as substituted amino-s-triazines having the following basic structure:

In the structure above, R1 is typically a halo gen (most often chlorine) or a cyanide radical; R2 and R3 are lower alkyl-substituted amino groups.

The method of the present invention may also be utilized in conjuction with the applica tion of a triazine herbicide to control selec tively the growth of weeds at the locus of an agronomic crop to which the triazine herbicide is phytotoxic. In this embodiment, the triazine herbicide is applied to the locus of the crop prior to emergence, preferably, although not necessarily, prior to planting. After a suitable time for the herbicide to act on the weeds and other undesired vegetation, the soil at the locus is assayed for a quantitative determina tion of triazine residue and an oxygen-releas ing compound is thereafter applied to the locus of the crop in an amount effective substantially to neutralize the herbicidal activ ity of the triazine residue.

It will be understood that depending upon the agronomic crop, the weed control tech nique referred to above permits planting of the crop seeds before, during and/or after application of the herbicide to the locus. Of course, for all crops, a preferred technique will be to remove the undesired vegetation and thereafter neutralize the herbicidal activity of the triazine prior to planting. However, in some instances it may be desirable or neces sary to wait until after planting to neutralize the herbicide or even to plant the seed prior -to application of the herbicide. This will de pend upon such things as the phytotoxic resistance of the seed, the manner in which the seed is applied to the locus (i.e. in furrows or simply within the top layer), etc, as will be appreciated by those skilled in the art.It is a very desirable feature of this invention that, within limits, exigencies such as weather emergencies or manpower and/or equipment utilization problems become less serious be cause of the flexibility of the weed control procedures which are permitted by the inven tion.

Those skilled in this art will recognize that the techniques described above for triazine herbicides are of general application and can be adopted by routine experimentation, to suit other types of herbicides and pesticides. For example, although optimum application pa rameters have not as yet been established, the neutralization technique of the present inven tion has been indicated as effective in degrad ing residues of halogenated aromatic hydro carbons, such as DDT (dichloro-diphenyl-tri chloroethane) and Treflan (trifluralin).

In a further aspect, the present invention provides an agricultural composition for use in degrading the toxic activity of an organic chemical pesticide remaining as a residue at the locus of previous use of such pesticide, which composition comprises an active oxygen-releasing compound which does not adversely affect the environment at said locus in combination with an agronomically acceptable carrier.

The invention also provides, in yet a further preferred aspect, an agricultural composition for use in degrading the toxic activity of triazine herbicide residues remaining in a field subsequent to treatment with such herbicide at residue concentrations below about 5 ppm, which composition comprises a water soluble potassium oxysulphate salt which releases active oxygen upon application to the soil in combination with an agronomically acceptable carrier.

The Active Oxygen-Releasing Compound Active Oxygen-releasing compounds are those compounds which contain oxygen in a relatively weak and unstable bonded state and in excess of that required to form a relatively stable compound. They are further characterized in that they release oxygen, in its active, nascent state as opposed to in a relatively inactive combined molecular form. The conditions which result in the release of active oxygen from such compounds vary considerably depending upon the compound, but are most often reached upon changes in temperature of pH or upon dissolution of the compound in water.

The presence of active oxygen in a compound may be determined in many ways. One particular convenient procedure, involving the displacement of iodine from potassium iodide, will give a quantitative as well as a qualitative determination.

The methods of the present invention require an active oxygen-releasing compound which is not only soluble in water, but is also environmentally safe. More importantly, the compound should be sufficiently stable (or ablt to be buffered to be sufficiently stable) in an environment of agronomic application such that the release of active oxygen is, or may be, controlled to ensure substantial contact of the active oxygen with the chemical pesticide to be degraded.

Of the many compounds which release active-oxygen, most will have a detrimental effect on the environment or will release the oxygen either too slowly or too quickly. Environmentally detrimental compounds are unsuitable for use in this invention. Further, compounds which release oxygen either too quickly for effective contact or too slowly will have to be used in such quantities as to be uneconomical in agronomic application.

Experiments have indicated that the alkali and alkaline earth metal oxysulphates may be available in compositions which are, or can be, stabilized to release active oxygen in a suitable fashion so as to be useful in the present invention. However, with the exception of the calcium salt, which may have limited application in some geographic areas, it appears that only the potassium oxysulphates possess the additional characteristic of causing no harmful effect to the enviroment.

There is also some indication that the percarbonates, particularly potassium percarbonate, may also have some application in the methods of the present invention.

The preferred stable, oxygen-releasing compound for use in the compositions and methods of the present invention is potassium monoperoxysulphate. This compound is sold in a particularly desirable ternary salt composition having the chemical formula 2KHSQ5 . KHSO4 . K2S04 under the trade name "OXONE" by E. I. du Pont de Nemours 8 Company of Wilmington, Delaware. This composition, which is described in, for example, United States Patent Specification No. 3,041,139 has the significant benefit of being relatively stable within a defined pH range.

Application Techniques An agronomic application in any application which would be utilized to treat the locus of a crop, including surface applications such as spraying, misting, dusting or scattering, and incorporation into the soil, as by discing, furrowing, or the like. It is feature of the prevent invention that the compounds recommended as active oxygen-releasing compounds for use in the methods of the present invention can be applied to the growth medium (that is, to, for example, the soil directly) or to the plants to be treated.While most situations will dictate that the composition be formulated as an aqueous solution, it will apprent to those skilled in this art that the active oxygen-releasing compounds utilized in the present invention may be applied to the soil dry and thereafter the active oxygenreleasing compounds to the locus of the crop will be dictated by many factors, all well within the skill of the art will be determined by those skilled in this art.

The most beneficial utilization of the invention method involves determination of soil pH at the locus of application. This is because most active oxygen-releasing salts, including the preferred potassium oxysulphate salts, are more stable and better able to be utilized within defined pH ranges. There are many standard techniques for assaying soil to determine pH, as will be well-known to those skilled in the art. Also, where is it desirable or convenient to assay the soil for a qualitative and/or quantitative determination of the pesticide residue, most assay tests for this purpose can be made to additionally provide a pH reading. For example, the assay test described in the Journal of Agr. Food Chemistry, Vol.

14, pages 70-73 (1966) for determination of 2-chloro-s-triazine presence also describes a pH test which may be conducted with the same soil samples.

When the assay shows the soil at the locus of application to be highly alkaline, a buffering agent may be necessary to ensure that the active oxygen-releasing agent is maintained within an acceptable range of stability. With the preferred potassium oxysulphate salts, sodium bicarbonate or sodium sulphate will be an effective buffer. As a rule, from about 1 to about 5 units of buffer per 100 units by weight of salt will be sufficient to maintain the stability of the active oxygen-releasing salt.

It should be noted that the safening effect of the active oxygen-releasing compounds useful in the methods of this invention is not compromised by the presence of nitrogen based fertilizers. Thus, compositions containing the compounds may also include fertilizers or fertilizing materials. The only limitation here is that the fertilizer should in most cases be a nitrogen-based fertilizer, such as ammonium sulphate or ammonium nitrate, because other typical components of commercial fertilizers, especially phosphates, may have a deleterious effect on the active oxygen-releasing compounds.

The preferred active oxygen-releasing sulphate salts have the additional advantage of not being affected adversely by the presence of organic matter. In fact, it appears to be the case that where organic matter is present in the soil or is added to the soil at the same time as the active oxygen-releasing agent, the degradative effect on the residual pesticide is enhanced, particularly where the pesticide is a chloro-s-triazine, such as Atrazine or Simazine.

This invention will be further explained by the following illustrative examples.

EXAMPLE 1 An assay of the soil of a 200 acre (80 Ha) field which had just been harvested of a corn crop determined that the field contained a residue of Atrazine herbicide uniformly distributed at a concentration of approximately 0.3 ppm. The field was treated with a formulation consisting essentially of potassium monoperoxysulphate (in the form of a commercially available preparation known by the Trade Mark OXONE, sold by du Pont), at a rate of 0.6 pounds per acre, (0.66 Kg/Ha). That is, a total of 55 Kg of the formulation was employed in treating the 200 acre (80 Ha) field.

The material was incorporated into the soild of the field by discing it in as a dry powder to a depth of 3 to 6 inches (7.5 to 15 cm). The field was left undisturbed for 48 hours after which time it was planted in soybeans. The second crop, which has no tolerance for Atrazine, even at extremely low levels, did well.

EXAMPLE 2 Attrex triazine herbicide was mistakenly applied, at a rate of 1.7 pounds per acre (1.9 Kg/Ha) to a field of already emerged soybean as a result of an overshot during aerial treatment of an adjacent field with the herbicide. A swath approximately 400 yards (365 m) lond was affected. Within seven days, the soybean crop began to wither and die. An application of potassium monoxysulphate was made by spraying an aqueous solution of the salt directly over the field at a rate of approximately 3.0 pounds of active oxygen-releasing compound per acre (3.4 Kg/Ha). Within 36 hours a definite improvement in the colour of the beans and the plants was observed. Approximately 40% of the crop was irretrievably destroyed, but 60% was saved. This example demonstrates that the beneficial effects of the method of the present invention may be obtained even post emergence.

EXAMPLE 3 Soybeans were planted in a field immediately following the harvest of a 1 977 corn crop. The soil had been assayed and showed no discernable herbicide down to a level of three inches (7.5 cm). Several weeks after the soybean crop had emerged, however, what appeared to be severe herbicide injury was noticed on some of the larger plants. It was determined that there were toxic levels of Atrazine in the soil deeper than three inches (7.5 cm) below the surface. Thus, those plants which were demonstrating the effect were those whose roots extended down further than three to four inches (7.5 to 10 cm), and it thus appeared that the herbicides was being taken up by the plants through the root system. The product not commercially sold under the Trade Mark NO-TOX (containing as its principal ingredient the OXONE product sold by Du Pont) was applied by air directly to the field at a weight ratio of the product to the herbicide of approximately 2:1 and was thereafter watered in on about one-half of the field.

The triazine injury was immediately stopped on that half with no further burn or chlorosis on any new growth. No therapeutic effect on those plants too severely damaged prior to the treatment was observed.

This example appears to demonstrate that the beneficial active oxygen-releasing salts of the invention are taken up by the plants themselves, through the root system and perhaps directly through the leaves, to degrade herbicide which is inside the plant system.

Claims (20)

1. A method for degrading an organic chemical pesticide remaining as a residue at the locus of previous use of such pesticide, which method comprises treating the locus, by a suitable agronomic application technique, with an active oxygen-releasing compound which does not adversely affect the environment at said locus in a manner such that an effective amount of active oxygen is release at said locus to contact said chemical pesticide residue.

2. A method according to claim 1, wherein the active oxygen-releasing compound is a potassium oxysulphate salt.

3. A method according to claim 2, wherein the potassium oxysulphate salt is potassium monoperoxysulphate.

4. A method according to claim 1, wherein the active oxygen-releasing compound is potassium percarbonate.

5. A method according to claim 1, wherein the pesticide is an insecticide.

6. A method according to any one of claims 1 to 4, wherein the pesticide is a triazine herbicide selected from the group consisting of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine, 2-chloro-4, 6-bis(ethylamino)-s-triazi ne, 2(4-ch loro-6-ethylamino-s-triaz ine-2-yl-amino)-2-methylpropionitrile, 2-chloro 4-cyclopropylamine-6-isopropylamino-s-triaz- ine, and combinations thereof.

7. A method for substantially reducing the herbicidal activity of a triazine herbicide residue at the locus of a previous application of said herbicide, which method comprises treating said locus, by means of any suitable agronomic application technique, with an environmentally safe active oxygen-releasing compound which releases active oxygen subsequent to its application at said locus.

8. A method according to claim 7, wherein said active oxygen-releasing compound is a potassium oxysulphate salt.

9. A method according to claim 8, wherein said oxysulphate salt consists of a stabilized potassium monoperoxysulphate.

10. A method according to claim 7, wherein said active oxygen-releasing compound is potassium percarbonate.

11. A method according to any one of claims 7 to 10, wherein the triazine herbicide is selected from the group consisting of 2chloro-4-ethylamino-6-isopropylamino-s-triazine, 2-chloro-4,6-bis(ethylamino)-s-triazine, 2(4-chloro-6-ethylamino-s-triazine-2-yl-amino)2-methylpropionitrile 2-chloro-4-cyclopropylamino-6-isopropylamino-s-triazine, and combinations thereof.

1 2. A method according to any one of claims 7 to 11, wherein the soil at the locus is assayed to obtain a quantitative determination of the amount of herbicide and said active oxygen-releasing comound is thereafter applied to said locus in such amounts that the mole ratio of active oxygen-releasing compound to triazine herbicide is in the range 0.5 :1 to 5.0 :1.

1 3. A method according to claim 12, wherein said mole ratio is about 2:1.

14. A method according to any one of the preceding claims, wherein said oxygen-releasing compound is buffered with sodium bicarbonate or sodium sulphate.

1 5. A method according to any one of the preceding claims, wherein said active oxygenreleasing compound is applied in the form of an aqueous solution.

1 6. An agricultural composition for use in degrading the toxic activity of an organic chemical pesticide remaining as a residue at the locus of previous use of such pesticide, which composition comprises an active oxygen-releasing compound which does not adversely affect the environment at said locus in combination with an agronomically acceptable carrier.

1 7. An agricultural composition composition for use in degrading the toxic activity of triazine herbicide residues remaining in a field subsequent to treatment with such herbicide at residue concentrations below about 5 ppm, which composition comprises a water soluble potassium oxysulphate salt which releases active oxygen upon application to the soil in combination with an agronomically acceptable carrier.

1 8. A method for degrading an organic chemical pesticide residue, substantially as herein described.

19. An agricultural composition for use in degrading the toxic activity of an organic chemical pesticide residue, substantially as herein described.

20. Any novel feature or novel combination of features disclosed herein.