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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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There have also been examples of international chemical companies selling a package of extension, training and pesticide programmes to the governments of developing countries, to the mutual advantage of all concerned.

The agricultural chemicals industry has considerable technical expertise, and experience in training technical and administrative staff, and would welcome the opportunity for greater co-operation with international organisations like FAO in the future.

There is also a strong case for aid donors to give more attention to the development of crop protection which can, when correctly applied, generate higher rates of return on investment than many large capital projects.

58 LEVER

–  –  –

The economic decision to use crop protection chemicals has been shown to have many financial and non-financial facets. Used correctly, and with an appreciation of the environmental risks, agricultural chemicals will continue to grow in importance, making a major contribution to the vital growth of agricultural productivity in the developing countries. Investment in the chemicals, and the extension.service to promote their correct and timely use will generate excellent economic returns.

–  –  –

[1] FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS,

Agriculture : Towards 2000, FAO, Rome (1981).

[2] HASKELL, P.T., "Can tropical crops be efficiently protected?", Proc. 11th British (see Ref 19) Insecticide Fungicide Conf. (1981), British Crop Protection Council, Croydon (1981).

[3] FREEMAN, J.A., "Food in store", Pesticides and Human Welfare (GUNN, D.L., STEVENS, J.G.R., Eds), Oxford University Press, Oxford (1976) 169.

[4] PATHAK, M.D., OU, S.H., DE DATTA, S.К., "Rice", Pesticides and Human Welfare (GUNN, D.L., STEVENS, J.G.R., Eds), Oxford University Press, Oxford (1976) 131.

[5] ADAM, A.V., "The importance of pesticides in developing countries", Pesticides and Human Welfare (GUNN, D.L., STEVENS, J.G.R., Eds), Oxford University Press, Oxford (1976) 115.

[6] RUSCOE, C.N.E.R., "Pyrethroids as cotton insecticides", Outlook on Agriculture JO. 4 (1980) 167.

[7] YEOH, C.H., LEE, K.A., LIM, H.H., PHONG, A.K., "Comparison of chemical and manual weeding in rubber nursery", Plrs Bull. Rubb. Res. Inst. Malaysia No 162 (1980) 28.

–  –  –

[9] DE DATTA, S.К., BARKER, R., "Economic evaluation of modern weed control techniques in rice", Integrated Control of Weeds (FRYER, J.D., MATSUNAKA, S, Eds), University of Tokyo Press, Tokyo (1977) 20 5.

–  –  –

[11] INTERNATIONAL INSTITUTE OF TROPICAL AGRICULTURE, Annual Report, U T A, Ibadan ( 1975) 160.

[12] INTERNATIONAL INSTITUTE OF TROPICAL AGRICULTURE, Zero tillage - an alternative to bush fallow, IITA Research Highlights Ibadan (1977) 1.

–  –  –

[14] WILSON, K.C., "Tea nutrition", Tea _10 3 (1969) 16.

[15] SETH, A.K., ABU BAKAR BIN BAHA, SIVARAJAH, S., "New recommendations for weed control in young oil palms", Planter 46 527 (1970) 32.

[16] BORLAUG, N.E., "Mankind and civilisation at another crossroads in balance with nature - a biological myth", Bio-Science 221 (1972) 41.

[17] INTERNATIONAL INSTITUTE OF TROPICAL AGRICULTURE, Grain Legume Improvement Programme, IITA Report, Ibadan (1973) 52.

[18] RAHEJA, A.K., "Yield losses from pests and the economics of chemical pest control in cowpeas in Northern Nigeria", Pests of Grain Legumes (SINGH, S.R VAN EMDEN, H.E., TAYLOR, T.A. Eds), Academic Press, London (1978).

[19] COFFEE, R.A., "Electrodynamic energy - a new approach to pesticide application, Proc 10th British Insecticide and Fungicide Conf. (1979), British Crop Protection Council, Croydon.

[20] METCALF, R.L., "Changing Role of Insecticides in Crop Protection", Ann. Rev. Entomol. 25^ (1980) 219.

–  –  –

[22] LEVER, В.G., "Some economic factors affecting choice of the sterile insect release method as part of a pest control programme", Sterility Principle for Insect Control 1974 (Proc. Symp. Innsbruck, 1974), IAEA, Vienna (1974) IAEA-SM-186/53.

PESTICIDES IN THE AGRICULTURAL

ENVIRONMENT

(Session II) Chairman

–  –  –

FATE OF PERSISTENT PESTICIDES IN THE AGRICULTURAL ENVIRONMENT WITH

PARTICULAR EMPHASIS ON THE APPLICATION OF NUCLEAR TECHNIQUES.

A selection has been made from open literature and from studies evaluated by the Joint FAO/WHO Meeting of Experts on Pesticide Residues over the past three or four years to show how isotope techniques have been applied during studies to determine the fate of pesticides in the agricultural environment. While many of these involve investigations to elucidate metabolism in plants, animals and soil, nuclear techniques are also useful in developing and validating analytical techniques and in determining the nature and level of residues transferred to and accumulated in foods of animal origin and the effect of processing and cooking on residues in food commodities of all types.

INTRODUCTION

Pesticides have provided tremendous benefits in the past, through the control of pests that affect man's health, destroy his sources of food, compete with his crops, and damage his belongings. They are toxic chemical compounds that must be treated with the same care and respect as pharmaceutical products and other developments of modern science and technology. There have been problems in the past due to their misuse or over-use but very rarely, if ever, from their proper use. Increasingly precise analytical procedures that can detect minute amounts of residues, the phasing out of undesirable chemicals, more comprehensive regulatory procedures and the less intensive use of pesticides through the development of integrated pest control systems will ensure a minimum of problems and a maximum of benefits from use of pesticides in the future.





An ever-increasing world population demands increased food, fibre and forage production, together with improved public health facilities for man's survival. Improved technology, including the judicious use of pesticides, helps man meet these demands.

Several important factors must be considered in connection with the use of pesticides in today's environment-conscious society. It must be recognised that vast airounts of time, money and effort are being expended to ensure that

–  –  –

these chemicals are capable of being used for the general betterment of mankind through the production of wholesome food and the protection of health. It is also clear that there are some very definite hazards and drawbacks involved when these products are used excessively or unwisely.

One fact that comes through very clearly is that pesticides are now, and will continue to be, an integral and essential part of most pest control systems.

The amount of pesticide used in any system or systems will inevitably vary according to the crop to be protected, the pest to be controlled, the nature of the compound itself and of factors such as biological and cultural control practices and climate. By the same token, it is safe to say that society's overall goal should be to use pesticides at the lowest possible levels within the socio-economic constraints of our society and to use them in a manner designed to minimise the risk of side effects.

The term "persistence" cannot be exactly defined. A substance is unduly persistent whenever a measurable quantity thereof continues to exist in some discernable chemical form. Obviously, the most desirable pesticide would be one that has a biological 'life' just sufficient to perform its function as a pesticide, with no residual carry over. Since this is difficult to achieve, the rhythm of use of the pesticide in terms of its function must always be considered. Therefore, "the function, time, rhythm" of a pesticide must take into consideration not only its biological 'life', but also its presence afterwards in terms of any residual terminal chemical.

The desirability of having rapidly bio-degradable pesticides appears attractive as theoretically this would prevent any residues. However, two questions arise; first, are the metabolites from degradation "ecologically safe" and second, how precise is the time of degradation? The first requires extensive study to identify the metabolites and their ecological effect while in the case of the second, conditions determining rate of degradation are important. With short-lived materials, the timing of application for insect control is usually much more critical than with more stable materials. The precision in timing may be well beyond the capabilities of farmers. In the case of insect pests with a long life cycle, a large reproductive capacity or an ability to migrate it would be necessary to apply such short-lived materials repeatedly and frequently with the result that the environmental impact could well be greater.

There are two facts which must be taken into account by the proponents of the use of persistent pesticides. They wander far away from the original area of application and they have been proven to be harmful to some species of fauna.

On the other hand, those who favour a complete ban on the use of persistent pesticides, including organochlorine insecticides, should realise that they serve a very valuable function in both public health and agriculture. In spite of claims that less toxic or less persistent materials could serve the same purpose, the expert opinion is that, for many applications, effective substitutes are not yet available.

There are real dangers. There are real advantages. Ways must be sought in which the potential harm can be diminished or eliminated. To accomplish this end, ecologists and physiologists must work together with agriculturists and public health officials.

When the Scientific Secretary responsible for this International Symposium on Agrochemicals invited me to present a review paper on "Persistent Pesticides in the Agricultural Environment" I assumed that I should confine my attention IAEA-SM-263/32 65 to the classical "persistent" pesticides. However, a detailed study of the scientific literature revealed that most of this work had already been reviewed at previous FAO/IAEA meetings and I could see no way in which I could present this information in a fresh light. Extensive correspondence with contacts in various tropical countries only served to confirm my views.

I therefore concluded that the recognition that the agricultural environment is finite and that all pesticides are persistent to some degree justified a review of recent studies of the effect of the various components of the agricultural environment on a variety of widely used modern pesticides. I have attempted to make such a review, paying particular attention to the application of nuclear techniques in studying these interactions.

THE APPLICATION OF NUCLEAR TECHNIQUES

It is interesting to consider how the application of isotope techniques has led to a more complete understanding of the properties, effects and fate of pesticides and how radiotracer studies now form a vital part of the multi-disciplinary approach to the study of new pesticides prior, as well as subsequent, to marketing. Before doing so I would like to draw attention to the report of a previous FAO/IAEA Research Co-ordination Meeting held in Vienna, 25-29 October 1971 [1] in which the value of isotopetracer techniques for obtaining complete information on the persistence and fate of foreign substances in living organisms and the environment is summarised in a few,

well-chosen words which are as true today as they were eleven years ago:

"Any foreign chemical added to food or the environment will always be present from that moment onwards either as the original chemical compound or as its equivalent derivatives and breakdown products. Fortunately, most foreign chemicals undergo sufficiently rapid physical dispersion and/or chemical degradation so that the resulting residues are of little or no ecological or toxicological significance. However, in assessing the possible significance of each residue in food or the environment in the first place, it is essential to obtain as complete a picture as possible of the fate and biological activity, not only of the parent compound but of all its likely derivatives. It is not sufficient to study the disappearance of the parent substance only. The derivatives may also be of significance in relation to possible concentration in food chains, chronic toxicity or long-term ecological effects. Isotope-tracer techniques have been found to be especially useful in basic studies of this kind and in the preparation of "balance sheets" to account for the overall fate of the original substance. Another advantage of the tracer technique is that it also provides information on metabolites, derivatives, etc. which may not be recovered or extracted by the usual analytical extraction procedures, especially from aged or stored samples."

If we were to measure the importance of isotope techniques by the number of scientific papers that appear in open literature or in unpublished studies presented to government authorities for evaluation, we would find that studies of metabolism in plants, animals and other environmental niches exceed all of the rest of the studies involving radiotracers. This is not only because of the importance of metabolism studies for evaluation of consumer safety, but because such studies go a long way towards providing a clear picture of the mode of action of the compound, its possible effect on livestock and wild life, the importance of application patterns and techniques, the possibility of phytotoxicity and similar side-effects and the likely influence of environmental factors. There is, in fact, no other convenient method for studying metabolism.



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