TIERED AQUATIC RISK REFINEMENT - CASE-STUDY - AT-PLANT APPLICATIONS OF GRANULAR CHLORPYRIFOS TO CORN

The tools of risk assessment are important in the management of enviro nmental risk from the use of agricultural chemicals. A tiered process of estimating and refining the risks from runoff to nontarget aquatic ecosystem is described. The methodology uses screening tools at the lo wer level of assessment and progresses to a probabilistic, geographica lly specific tool at the highest tier level. The tools are demonstrate d by an analysis of the risks to aquatic ecosystems resulting from the use of granular chlorpyrifos on corn. Vegetative filter strips and re duced tillage were examined as potential best management practices to reduce runoff impact. In addition, data from outdoor microcosm experim ents were used to refine toxicity endpoints. The combination of runoff reduction and endpoint refinement resulted in a two-to 16-fold reduct ion in potential risk, based on 90th percentile endpoints. The results also located where more localized efforts in product stewardship, use r education, potential field research, or more refined assessment may be beneficial. The simulation results are compared to field monitoring results.