GB2277587A

GB2277587A - Enviromental monitoring

Info

Publication number: GB2277587A
Application number: GB9407666A
Authority: GB
Inventors: Michael Harry Tinker; John Alexander Cole
Original assignee: WRC PLC
Current assignee: WRC PLC
Priority date: 1993-04-19
Filing date: 1994-04-18
Publication date: 1994-11-02
Anticipated expiration: 2014-04-18
Also published as: GB9308016D0; GB2277587B; GB9407666D0

Abstract

An environment is monitored, for example for pollution, by detecting changes in the movements of plant materials or animals which are very small, i.e. no larger than 3000 mu m. These materials and animals include, for example, algae, protozoa, microorganisms, insects, pollen, spores and seeds. The environment is normally gaseous or aqueous. In one arrangement, a vessel V contains the plant material or animals, and their movements are detected by use of a light beam L from a source C, to display a speckle pattern on a screen S, the speckle pattern being inspected and measured to obtain movement information. Alternatively, the light beam L can be combined with a reference beam to give an interference pattern containing doppler frequencies indicative of organism movement. <IMAGE>

Description

ENVIRONMENTAL MONITORING This invention relates to environmental monitoring and to apparatus useful therefor.

It is known that the active behaviour of fish is an indicator of their living functions and that changes in behaviour can indicate a change in their aquatic environment. Thus, for example, changes in the gill movements and swimming activity of fish have been used as indicators of the presence of pollutants in waters to which the fish are exposed. The behaviour of luminescent bacteria has also been used to detect pollutants.

We have now found that it is possible to monitor changes in an environment by detecting movements in or of very small plant materials and very small animals which are exposed to the environment. By observing the movements, it is possible to monitor changes in the environment itself, eg. the arrival and/or presence of pollutants.

Thus, the invention provides a method of monitoring an environment which comprises detecting movements in or by small plant materials or animals, exposed to the environment.

The invention also includes apparatus for carrying out the method, which apparatus comprises means for containing the small plant material or animals, means for exposing them to the environment, and means for sensing their movements upon said exposure.

Whilst the invention is particularly concerned with aquatic and atmospheric (or other gaseous) ~environments, it can be used in other different circumstances.

The animals and plant materials used in the invention can vary widely but they are all small, i.e. they are no larger than 3000 m and, more usually, are up to about 1000 m in size. They may be very small indeed, eg. algae of about 2 m in size. Examples include algae and protozoa, bacteria and other microorganisms, and small insects, and pollen, spores and fine seeds. Preferred organisms for use in the invention include Paramecium and flagellate types of algae.

The movements in small animals which can be detected include free swimming, ciliary beating and various intra- and extra-cellular motions. Any or all of these movements can be affected by the presence of harmful substances in the environment, so that measurement of the organisms' individual or collective behaviour can be used to monitor aquatic pollution.

In gaseous environments, the behaviour of pollen, spores, fine seeds and other plant materials, or of small animals can be observed. Thus, for example, the flight movements of small insects can be observed, in order to detect their response to gaseous chemicals.

In order that the invention may be more fully understood, reference is made to the accompanying drawings in which: Fig. 1 is a schematic illustration of one embodiment of apparatus in accordance with the invention; and Figs. 2 and 3 are graphs of spectral power against frequency as described in Examples 1 and 2, respectively.

Referring to Figure 1, there is shown a beam of light (L), arising from a coherent source C, that traverses a transparent vessel V containing a living sample of small organisms. Typically this sample would be an aqueous suspension of algae or protozoa, but alternatively it could be an aerosol of pollen, spores, fine seeds or small insects.

The scatter of the coherent light generates an optical image in the form of a speckle pattern on a screen S further down the light path. The movements of the organisms in the vessel exposed to the light beam produce continual shifts in the speckle pattern. By putting an optical detector or detectors D to one side of the main beam and then analysing the frequency and spatial distribution of the received signal, information is gained on the motile behaviour of organisms in the sample.

The invention includes: 1. the use of coherent light to produce an optical pattern after the light has traversed a sample holder containing the micro-organisms, in a liquid or gaseous suspension.

2. the use of speckle pattern as the means of inferring movements of the micro-organisms.

3. the use of fast Fourier transform apparatus to analyse the speckle signals.

4. the use of cross-correlation apparatus to analyse the speckle signals.

5. apparatus for carrying out the above procedures.

A closed-circuit television camera may also be used to record the speckle pattern, for subsequent analysisoff-line.

An alternative way of measuring motile behaviour in accordance with the invention uses a split beam of coherent light, one beam going through the suspension of small organisms or plant material and the other beam acting as a phase reference. By recombination of the two light beams, the organisms'/plant material movements are revealed as an interference pattern containing doppler frequencies.

Another variation of the invention employs a positional modulation of the cell containing the microorganisms. This may be achieved by affixing the cell to a piezo-electric or electromechanical transducer. At sufficiently high vibratory frequencies the swimming organisms are effectively stationary within a modulation period, their positions being modulated purely by the transducer, and a full speckle modulation at twice the imposed frequency is seen. As the modulation frequency is reduced progressively there comes a point at which the swimming movements of each organism within a modulation period are significant with respect to the size of the organism and the speckle modulation amplitude is reduced.By sweeping the modulation frequency and simultaneously observing the amplitude of the in-phase response of the speckle pattern, the mean swimming speed of the micro-organism can be inferred.

In order that the invention may be more fully understood, the following Examples are given by way of illustration only.

ExamDle 1 Using the apparatus of Figure 1, the following tests were made.

A few millilitres of the organism Tetrahvmena rracilis were introduced into the cuvette V, which had already been fixed in the line of the laser beam, on an optical bench. The apparatus had already been optically - aligned, with a photodetector D set just off-axis, 2 metres down the light path from the cuvette. A lid was then closed to exclude extraneous light.

The laser was started and after a few minutes the shutter was opened to illuminate the cuvette. The resulting speckle behaviour was then measured at a fixed point by the photodetector, whose electrical signal was amplified and led to an electronic Fast Fourier Transform (FFT) analyser. The FFT expresses the relative amplitude of the signal over a range of frequency, typically the signal voltage is on a logarithmic decibel scale and the frequency range covers 0 to 200 Hertz or 0 to 500 Hz, depending on the test organism.

Graph N in Fig. 2 illustrates the FFT for Tetrahvmena culture, before addition of any toxicant.

The graphs P, Q and S represent the effect of adding a copper salt to the culture, the FFT spectrum first moving slightly to higher frequencies, and then progressively sinking to lower and lower ones.

Observations on an undosed culture produce a relatively stable FFT, which does not alter much over time.

Example 2 Example 1 was repeated but using the organism EntosiDhon sulcatum.

Results are presented in Fig. 3, on a 0 to 200 Hz frequency range. Graph M shows the FFT of the pure culture, which systematically exhibits small maxima at approximately 16 Hz and 90 Hz. After being dosed with a copper salt these maxima collapse and the whole FFT progressively sinks to lower frequencies, which does not occur in the case of an undosed culture.

The Examples illustrate the way in which copper contamination can be detected. The same technique can be used for other dissolved metals, using organisms sensitive thereto.

Claims

CLAIMS:

1. A method of monitoring an environment which comprises detecting movements in or by plant materials or animals exposed to the environment, the plant materials and animals being no larger than 3000 um.

2. A method according to claim 1, wherein the plant materials and animals are selected from algae, protozoa, microorganisms, insects, pollen, spores and seeds.

3. A method according to claim 2, wherein the animals are bacteria, Paramecia or flagellate types of algae.

4. A method according to claim 1,2 or 3, wherein the environment is liquid and the movements which are detected are free swimming, ciliary beating, or intra- or extracellular motions.

5. A method according to claim 1,2 or 3, wherein the environment is gaseous.

6. A method according to any preceding claim, wherein the movements are detected by light diffraction.

7. A method according to claim 6, wherein a speckle pattern is used to detect said movements.

8. A method according to any of claims 1 to 5, wherein said movements are detected by using a split beam of light.

9. A method according to claim 1 or 2, wherein movements of microorganisms in a cell are detected by positional modulation of the cell.

10. A method of monitoring an environment substantially as herein described with reference to the accompanying drawing.

11. Apparatus for monitoring an environment, which comprises means for containing plant materials or animals which are no larger than 3000 um; means for exposing the plant materials or animals to the environment; and means for sensing their movements upon said exposure.

12. Apparatus according to claim 11, wherein said containing means is a vessel, and said sensing means includes a light source to transmit a beam of light to traverse the vessel.

13. Apparatus according to claim 12, wherein means are provided to generate a speckle pattern.

14. Apparatus according to claim 12, wherein the sensing means includes means to split the light beam into two, only one of which traverses the vessel, and to recombine the two and establish an interference pattern.

15. Apparatus according to claim 13 or 14 which includes means to sense the time-wise fluctuations in the speckle or interference pattern, and to analyse the power spectrum of the fluctuations.

16. Apparatus according to claim 11, wherein the containing means is located to a movement transducer, means are provided to vibrate the containing means at varying frequencies; and means for sensing the apparent movement of animals in the containing means.

17. Apparatus for monitoring an environment substantially as herein described with reference to the accompanying drawing.