Predicting pesticide environmental risk in intensive agricultural areas. II: Screening level risk assessment of complex mixtures in surface waters.

In a previous article, a procedure for assessing pesticide ecotoxicological risk for surface water was applied to all active ingredients in a pilot basin. This data set has been used to assess the composition of pesticide mixtures that are likely to be present in surface waters as a consequence of pesticide emissions from the crops grown within the basin (maize, soybean, sugar beet, and vineyard). Temporal evolution of the mixture composition has been evaluated as a function of the different contamination patterns (drift and runoff). Ecotoxicological risk has been assessed for the mixtures released by individual crops and from all the relevant crops cultivated in the basin. The different role of drift and runoff, as well as the temporal trends of exposure and risk are compared. Daphnia is the most affected among the three indicator organisms considered, particularly from drift mixtures after insecticide application on vineyard. The highest risk for algae occurs during runoff events in spring. In most risk events, one or a few chemicals are usually responsible for more than 80% of the toxic potency of the mixture. The CA model for predicting mixture response is assumed to be a reliable approach for assessing risk for ecologically relevant pesticide mixtures.