Chlorpyrifos: Ecotoxicological risk assessment for birds and mammals in corn agroecosystems

A tiered risk assessment was conducted for the use of granular and liquid f ormulations of chlorpyrifos in corn agroecosystems in the U.S. The initial screening Tier I assessment suggested that under high-exposure scenarios th e granular and some spray formulations present potential hazards to birds. Higher tiered probabilistic risk assessments were conducted separately for the granular and liquid formulations. The probabilistic assessment indicate d that risk to birds from exposure to granular formulation is small and tha t this route of exposure would not be a significant source of mortality. Si milarly, the assessment of potential exposure of birds to food items contam inated with chlorpyrifos showed that the risk from exposure via food was sm all, even if it was assumed that birds feed only on the treated fields. Alt hough they have potentially greater sensitivity to chlorpyrifos, effects in nestling birds consuming food items from fields treated with granular chlo rpyrifos were negligible. However, risks to young birds may be greater wher e the major source of food is from fields treated with liquid formulations of chlorpyrifos. A review of field studies showed that wildlife mortality i ncidents associated with use of either granular or liquid formulations of c hlorpyrifos are not widely apparent in agroecosystems. Based on the multipl e lines of evidence, we conclude that the presumption that chlorpyrifos use in corn agroecosystems will result in extensive mortality of terrestrial w ildlife, particularly birds and mammals, is not supported by the scientific evidence.