Effect of vegetative filter strip pesticide residue degradation assumptions for environmental exposure assessments.

Understanding and simulating the fate and transport of pesticides from a field to adjacent receiving water bodies is critical for estimating long-term environmental exposure concentrations (EECs) in regulatory higher-tier environmental exposure assessments (EEA). The potential of field mitigation practices like vegetative filter strips (VFS) to reduce pesticide pollution is receiving increasing attention. Previous research has proposed a modeling framework that links the US Environmental Protection Agency's (US-EPA) PRZM/EXAMS higher-tier EEA with a process-based VFS model (VFSMOD). This framework was updated to consider degradation and carryover of pesticide residue trapped in the VFS. However, there is disagreement on pesticide degradation assumptions among different regional EEA regulations (i.e. US or European Union), and in particular on how temperature and soil moisture dynamics may affect EECs. This research updated the VFS modeling framework to consider four degradation assumptions and determine if VFS residues and/or EECs differed with each assumption. Two model pesticides (mobile-labile and immobile-persistent) were evaluated for three distinct agroecological scenarios (continental row-crop agriculture, wet maritime agriculture, and dry Mediterranean intensive horticulture) with receiving water bodies and VFS lengths from 0 to 9m. The degradation assumption was important in long-term assessments to predict VFS pesticide residues (statistically different at p<0.01). However, due to the relatively small contribution of residues on the total pesticide mass moving through the VFS, degradation assumptions had a negligible impact on EECs. This indicates that, while important differences exist between EU or US EEAs, the choice of pesticide degradation assumption is not a main source of these differences.