Understanding Pesticide Exposure Mitigation Effectiveness in Achieving Endangered Species Protection Goals

To protect the environment, pesticides often require mitigation measures to reduce losses via runoff, erosion, spray drift, and other routes of transport. Although many mitigation measures are generally effective at reducing pesticide losses from treated areas, it is often unknown whether they provide the desired protection level for the environment including threatened and endangered (“listed”) species. In this paper, we use the Agricultural Policy/Environmental eXtender model (APEX) to quantify reductions in pesticide losses via runoff and erosion for common mitigation measures. These measures are currently being considered for the protection of listed species in the United States (i.e., vegetative buffers, contour cropping, planting of cover crops, and no-till practices). Analyses were conducted for two pesticides, atrazine and pendimethalin, for each of the two crop groups, corn, and vegetables/ground fruits. Separate analyses were conducted for different hydrologic regions, in which these crops are grown in the United States. Our results indicate that the effectiveness of the runoff mitigation measures, whether singly or in combination, varies with pesticide, crop, and region. We also found that there are diminishing returns as more mitigations are added to the analysis. Such factors need to be considered when developing suites of potential mandatory pesticide mitigations (i.e., pick lists) for the protection of threatened and endangered species in the United States.