Ecotoxicological Risk Assessment of Pesticides Subject to Long-Range Transport

Concern has arisen about the possible ecological effects of persistent pesticides that become airborne during or after application and are transported to regions far away from where they were applied. In this paper an ecotoxicological approach is outlined that may support assessments of products suspected of long-range transport capacity. It is proposed that the risk is estimated from a classical PNEC/PEC comparison for the surface layer of a remote area, where PEC is estimated from dose rate, emission factors, atmospheric residence time and persistence, while PNEC is estimated from ecotoxicological information collected as part of the registration procedure. According to this "null model", risk assessment of pesticides subject to long-range 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 concentration in the remote area is higher than in the target area only if its residence time is at least two order of magnitude longer than the corresponding value in the target area. A review of ecotoxicity data for effects of volatile pesticides on arthropods indicates that effect levels in the air compartment are far above the concentrations of concern in long-range transport. 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 residues of organochlorines are of concern, there does not seem to be concrete epidemiological or experimental evidence about effects of modern pesticides 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 uncertainty involved, it is proposed that the maximum acceptable ratio between PNEC and PEC be increased by an extra safety factor.