Ecotoxicological risk assessment of pesticides subject to long-range transport

Concern has arisen about the possible ecological effects of persistent pest icides that become airborne during or after application and are transported to regions far away from where they were applied. In this paper an ecotoxi cological approach is outlined that may support assessments of products sus pected of long-range transport capacity. It is proposed that the risk is es timated from a classical PNEC/PEC comparison for the surface layer of a rem ote area, where PEC is estimated from dose rate, emission factors, atmosphe ric residence time and persistence, while PNEC is estimated from ecotoxicol ogical information collected as part of the registration procedure. Accordi ng to this "null model", risk assessment of pesticides subject to long-rang e transport is not different from the usual risk assessment, provided that due attention is paid to losses occurring during transport and accumulation in remote areas with low temperature. A simplified equation is derived for estimating PEC from the recommended dose rate, which shows that the concen tration in the remote area is higher than in the target area only if its re sidence time is at least two order of magnitude longer than the correspondi ng value in the target area. A review of ecotoxicity data for effects of vo latile pesticides on arthropods indicates that effect levels in the air com partment are far above the concentrations of concern in long-range transpor t. Arguments supporting the view that remote areas, specifically the polar regions, are characterized by ecosystems that are more vulnerable than the ones on which the usual risk assessment is based, are reviewed. Although re sidues of organochlorines are of concern, there does not seem to be concret e epidemiological or experimental evidence about effects of modern pesticid es on wildlife in remote areas. It is concluded that there is no reason to reject the "null model" at the moment, however, in view of the large uncert ainty involved, it is proposed that the maximum acceptable ratio between PN EC and PEC be increased by an extra safety factor.