Chlorpyrifos is an insecticide approved globally for use on a wide range of crops. Laboratory studies indicate that chlorpyrifos is toxic to fish and aquatic invertebrates, and so the adoption of practices that reduce aquatic exposure following use should be encouraged. This study assessed the exposure of surface water to the spray-drift of chlorpyrifos and the subsequent contamination of a realistic worst-case edge-of-field ditch in a vineyard in Northern Italy. Chlorpyrifos (DURSBAN 480 EC [Dow Elanco, Indianapolis, IN, USA]) was applied according to local Good Agricultural Practice (GAP) on two vineyard plots using atomizer equipment. Drift deposition and subsequent dissipation of chlorpyrifos were then monitored in an adjacent, common ditch, with an inherent buffer zone of approximately 7 m between the treated area and the ditch. The results showed that the drift loadings under the study conditions could reach predicted levels from standard spray-drift tables. However, the measured drift was highly variable due to physical factors such as the crop canopy and the distribution of vines within the rows. The amount of chlorpyrifos deposited onto the surface of the ditch water and intercepted by paper strips was approximately 2% of the applied amount after the two applications, with a maximum concentration of approximately 0.3 microg L(-1) immediately after the first application and 0.09 microg L(-1) after the second, which then dissipated from the water column within 12 to 24 h. The results showed that drift deposition spatially was variable and that chlorpyrifos residues dissipated rapidly from this surface water body. Both aspects are considered important in order to refine the aquatic risk assessment at a higher tier for both registration and management purposes.

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The study is a good example of probabilistic risk assessment. The means of mean and SD posterior estimates of log BCFworm (2.06, 0.91) are the 'best estimate values'. Further risk assessment of quinoxyfen and other phenoxyquinoline fungicides and realistic representative scenarios for modelling exercises required for future authorization and post-authorization requirements can now use this value as input.