Markus D. Müller, Thomas Poiger and
Bruno Patrian, Plant Protection Chemistry, Federal Research Station, 8820
Wädenswil
The use of pesticides is tightly regulated in most countries in order to safeguard agricultural crops from damage by pests and to protect the environment and non-target organisms from adverse effects from exposure to these compounds. The registration process includes a prospective assessment of the fate of pesticides is an integrated benefit-risk evaluation. As pesticides - the technical active ingredients as well as formulated products - belong to commodities which are traded globally, several international bodies such as FAO, SETAC, OILB and OECD commit their activities to the international harmonization of guidelines on how to perform studies documenting the environmental fate of pesticides and on how to combine these studies into a dossier for submission to national authorities. The following outline of the assessment process is therefore valid not only for Switzerland but also for the European Union and most OECD-countries.
Briefly, most countries use the following tiered approach:
· Model studies in soil: 14C-labeled pesticides are incubated in soil under both aerobic and anaerobic conditions whereby the rate of degradation and the degradation products are determined and a mass balance is established. The sorption of the pesticide and its relevant metabolites is determined in batch equilibrium studies.
· Model studies in water and in sediment-water-systems, again with labeled compounds: hydrolysis, photolysis, biodegradation, and distribution between sediment and water are determined.
· Model studies in air, if the compound is at least somewhat volatile.
The results of laboratory studies may trigger more detailed (higher tier) studies such as field dissipation and lysimeter studies. Based on a defined set of studies, the experts of the national authorities deduce predicted environmental concentrations (PECs) taking into consideration the use rates of the formulated product in the range of crops. The PECs in soil and surface water are evaluated in terms of possible adverse effects to representative organisms (e.g. earthworms, algae, fishes).
Whereas the guidelines for the studies seem well established, the process of the extrapolation of the findings and conclusions from these studies to real world situations is still evolving in many countries. Nevertheless, a considerable degree of environmental safety has already now been achieved – at still rising costs for the companies conducting research for new active ingredients and for the registration authorities.