How does crop type influence risk from pesticides to the aquatic environment?

National-level risk mapping was undertaken to identify specific situations within England with the greatest potential for impacts on aquatic biodiversity from normal agricultural use of pesticides. Calculations of exposure via spray drift and drainflow were differentiated by landscape type, region, and crop and then compared with toxicity to the indicator organisms Daphnia magna and algae. The approach incorporated regional-level information regarding pesticide usage derived from farm visits. Risk was calculated for individual water bodies and then aggregated and mapped for each of 5,760 individual catchments ranging in area up to 248 km(2). Type of crop adjacent to water was the major driver for risk, and orchards were identified as the crop associated with the greatest potential risk to the aquatic environment. Crops such as cereals, oilseeds, and potatoes are more widely grown in England but have potential risk an order of magnitude smaller than that for orchards. Several of the pesticides that contribute most to risk have been withdrawn from use since collection of the most recent usage data. Driven by crop distribution, surface waters adjacent to orchards in the midwest and southeast of England are predicted to be most at risk of ecological impacts from agricultural pesticide use. This information can be used in targeting monitoring campaigns designed to protect the aquatic environment.