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«: AGROCHEMICALS: FATE IN FOOD AND THE ENVIRONMENT PROCEEDINGS OF A SYMPOSIUM, ROME, 7 - 1 1 JUNE 1982 JOINTLY ORGANIZED BY IAEA AND FAO l^J I N T E R ...»

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(2) Experiments should be planned between the IAEA and its collaborators in tropical climates to determine the half-lives of, initially, DDT, technical BHC, and possibly lindane. These experiments should be designed to include degradation in soils, on and in plants, and aquatic environments in order to compare differences between temperate and tropical conditions.

(3) The effectiveness o f microbial degradation must be considered in the soil studies.

(4) Volatilization o f unchanged pesticides must be taken into account in the experimental designs.

HERBICIDES IN THE TROPICS

Owing to the very rapid increase in the use o f herbicides in developing countries, primarily under tropical conditions, the consultants' group recommended consideration o f two research programmes: for effective chemical control o f Imperata cylindrica (L.) beauv. and related weeds, and for improving weed control in aquatic ecosystems.

Imperata cylindrica and related weeds are among the ten most damaging pest weeds in the world. This weed infests enormous land areas in the tropics and effective chemical control has not yet been developed. Little is known about the absorption and metabolism o f herbicides by this weed. Studies with radiolabeled herbicides would readily answer these questions and, as a continuation, it may be possible to develop special formulations o f herbicides that would control this weed effectively.

Regarding weed control in aquatic systems, the primary technical difficulties at present involve herbicide application technologies that effectively control water weeds while not causing environmental problems involving fish, use o f the water for human consumption, etc. Some work has been done on herbicide formulations, specifically for aquatic situations, and the consultants urged that this be used as a building block for the Joint F A O / I A E A Division programme. Radiolabeled herbicides are ideal for these studies because of precise answers that can be obtained on movement and distribution of the herbicide in water, uptake by the plant, inactivation in sediments, and metabolism of the herbicide in the water, and in the plant.

In both programmes, the consultants listed possible research contractors and research agreement holders.

SUMMARY REPORT 339

–  –  –

1. INTRODUCTION This report documents the recommendations o f the Third Research Co-ordination Meeting on Agricultural Chemical Residue-Biota Interactions in Soil and Aquatic Ecosystems, which was held concurrently with the Symposium.

The accomplishments o f the programmes are reviewed and proposals for the future activities and direction o f the programmes are presented.

Use o f agrochemicals will continue to be indispensable in the desperate battle o f mankind against starvation. Agrochemicals are essential ingredients in agricultural production. Environmental contamination represents unwanted side-effects o f agrochemical use. Frequent monitoring of the fate and effects o f pesticides in the environment is necessary because these chemicals are subject to continuous change. Nuclear techniques are an essential tool in this context.

Both isotope tracer techniques and labelled substrate techniques are used and are found to be o f great importance in this field. With the aim o f promoting extension o f this research and monitoring to developing countries, the Joint

F A O / I A E A Division initiated two co-ordinated research programmes:

(a) Isotopic tracer-aided research and monitoring programme on Agricultural Residue-Biota Interactions in Aquatic Ecosystems (water programme) in 1975,

which had the objectives:

(i) T o develop, standardize and apply isotopically labelled substrate techniques for comparative assays o f primary autotrophic and micro-heterotrophic production and decay (ii) To develop, standardize and apply complementary isotopic tracer techniques to determine fate, persistence and bioconcentration of trace contaminants (iii) T o use these techniques to obtain comparable data on the current status o f water bodies and the changes to be expected.

(b) Isotopic tracer-aided studies o f Agrochemical Residue-Soil Biota Interactions (soil programme) in 1977, which had the objectives:

(i) T o develop and evaluate labelled substrate techniques for measuring the soil capacity to decompose undesirable contaminants and residues and to promote desirable transformations (ii) T o perform comparative studies o f the fate and biological effects o f selected agrochemical residues and additives, and o f soil biological activity (iii) T o apply the techniques as a diagnostic tool, with priority to be given to rice ecosystems.

–  –  –

2. OBJECTIVES

The following objectives were outlined at this meeting:

(a) T o review the progress o f the programme (b) T o discuss the problems related to methodology and labelled substrates (c) T o discuss application o f a c o m m o n methodology developed since the previous Research Co-ordination Meeting (d) T o prepare for publication the scientific data and information obtained since the last report (IAEA-TECDOC-247, 1981) (e) T o identify the problems and priorities o f related subject areas and to make appropriate recommendations.





3. ACHIEVEMENTS

The contributions o f the programme participants were presented at the Symposium. The results were discussed by a larger group o f scientists and they attracted generally favourable comments. In a separate meeting, the programme participants reviewed the results and highlighted the achievements.

They commented that the system o f research programmes is quite satisfactory.

Major importance lies in development o f an international understanding o f the subject matter. The programme was successful in the sense o f having established over the years an excellent co-operation and exchange o f experience among the participants. Through scientific visits, close collaboration was established among scientists from developing and developed countries.

Some highlights are presented in the following sub-sections.

3.1. Water programme

Studies in Hungary showed that the labelled substrate-anti-cholinesterase method is a simple, sensitive and reliable tool to estimate specific pesticide residues in rivers and lakes. Application o f the labelled substrate-heterotrophic activity technique in fresh water fish ponds has been demonstrated in Canada and Israel. With the help o f this technique it was concluded that the tolerance o f parathion in this system is 30 ppb for a single treatment and that repeated treatments with 15 ppb, if a recovery time o f 3 to 7 days is allowed, are also tolerated.

Algal growth measurements using 14C02 correlated well with other primary production measurement methods. It was shown to be a g o o d monitoring method for water quality, both o f an Indonesian river system and o f a lake in the Federal Republic o f Germany. Use o f labelled substrate techniques for estimating the nitrogen and the carbon cycles in fresh water lakes has been demonstrated in the United States o f America.

SUMMARY REPORT 345 The fate o f the herbicide dichlobenil in Yugoslav irrigation channels was investigated, using a radiolabeled chemical. A half-life was estimated and some metabolites could be identified. Accumulation and effects o f radionuclides, heavy metals ( 2 1 0 P b ) and DDT were studied in connection with paper mill effluents in Baltic estuaries. Under certain conditions aquatic plants and algae were found to accumulate considerable amounts o f the contaminants, to the disadvantage o f some algal species.

3.2. Soil programme

Despite some promising publications and laboratory attempts, use o f labelled substrates to investigate agrochemical effects in the soil environment is not as well developed as in the aquatic system. Labelled substrates are, however, used to demonstrate effects on the metabolism o f soil organisms in vitro. In India it was found that nitrogen fixation o f cowpea plants was inhibited by herbicides at a concentration o f 5 to 10 ppm. This was correlated with a reduced metabolism o f labelled substrates by the Rhizobia strains. In the US it was found that at application levels o f 25 ppm atrazine began to exert an inhibiting effect on the appearance of gaseous denitrification products. In Iraqi soils nitrogen fixation and 14 C-glucose respiration were only inhibited at very high concentrations o f benlate, sevin and dipterex.

On the other hand, in the US, Turkey and Brazil labelled pesticides are widely used in the soil ecosystem as a unique tool to investigate pesticide residues and metabolites. In Austria it has been shown that, under certain conditions, elements such as zinc, mercury and cadmium accumulate to undesirable concentrations in some crop plants, although the edible parts usually have lower concentrations compared with other plant parts.

4. RECOMMENDATIONS The following recommendations were outlined to ensure essential continuity and the most effective contribution o f related research programmes

to the growing problems o f environmental contaminants:

(a) T o initiate, as funds become available, a co-ordinated research programme with the possible title o f Fate o f Pesticides and their Effects in Soil and Water Environments o f Tropical and Non-tropical Regions. The programme should include the flooded soils o f rice fields. A condition for participants in the programme is that they would undertake c o m m o n experiments.

(b) T o allocate extra funds for procurement of agrochemicals and their metabolites.

346 SUMMARY REPORT (c) T o continue publication o f scientific documents, since they were found to be o f great value to institutes, especially in developing countries, where literature sources are often limited.

(d) T o hold future Research Co-ordination Meetings at locations where the work is being done, preferably in developing countries, as previously recommended in IAEA-TECDOC-247, 1981.

5. CONCLUSIONS

In the light o f the original objectives and earlier recommendations, the meeting noted with satisfaction that the programme had achieved most o f its goals. Labelled substrates and other isotopic tracer techniques have been improved and their use has been extended to applications in developing countries.

Comparative assays have been devised that are ready to be applied whenever required. Results obtained with the techniques in various countries generally confirmed that pesticides, when used at the recommended levels, do not reach alarming concentrations in f o o d and the environment. It should be stressed that the results are preliminary and some aspects, such as the possible differences between pesticide behaviour in tropical and temperate zones, need further investigation. A topic that requires specific attention is temporarily and permanently flooded soil. There is insufficient information on the transport o f agrochemicals from agricultural land into water bodies. Rice field water, running from one field into the other, is likely to increase residues on its way.

It is concluded that there is a greater need to use tracer methodologies to help solve these problems.

SUMMARY REPORT



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