Environmental risk assessment for pesticides in the atmosphere; the results of an international workshop

The Health Council of the Netherlands organised an international workshop o n the fate of pesticides in the atmosphere and possible approaches for thei r regulatory environmental risk assessment. Approximately forty experts dis cussed what is currently known about the atmospheric fate of pesticides and major gaps in our understanding were identified. They favoured a tiered ap proach for assessing the environmental risks of atmospheric dispersion of t hese chemicals. In the first tier a pesticide's potential for emission duri ng application, as well as its volatilisation potential should be assessed. Estimates of the former should be based on the application method and the formulation, estimates of the latter on a compound's solubility in water, s aturated vapour pressure and octanol/water partition coefficient. Where a p esticide's potential for becoming airborne exceeds critical values, it shou ld be subjected to a more rigorous second tier evaluation which considers i ts toxicity to organisms in non-target areas. This evaluation can be achiev ed by calculating and comparing a predicted environmental concentration (PE C) and a predicted no-effect concentration (PNEC). By applying an extra unc ertainty factor the PNEC can be provisionally derived from standard toxicit y data that is already required for the registration of pesticides. Dependi ng on the distance between the source and the reception area, the PEC can b e estimated for remote areas using simple dispersion, trajectory type model s and for nearby areas using common dispersion models and standard scenario s of pesticide use. A pesticide's atmospheric transport potential is based on factors such as its reaction rate with OH radicals. It should be used to discriminate between those compounds for which only the risks to nearby ec osystems have to be assessed, and those for which the risks to remote ecosy stems also have to be determined. The participants were of the opinion that this approach is, in principle, scientifically feasible, although the rema ining uncertainties are substantial. Further field and laboratory research is necessary to gain more reliable estimates of the physico-chemical proper ties of pesticides, to validate and improve environmental fate models and t o validate the applicability of standard toxicity data. This will increase both the accuracy of and our confidence in the outcome of the risk assessme nt.