Importance of surface pesticide residues in the quantitative mitigation of pesticides with vegetative filter strips: VFSMOD development and analysis

Regulatory exposure assessments (EA) are a cornerstone in the registration of new or existing agrochemicals in the EU, USA and many other countries to preserve ecosystem health and water quality. VFSMOD (Muñoz-Carpena et al., 1999; 2004) is a numerical, storm-based design model that quantifies the performance of vegetative filter strips- VFS (grass buffers) to mitigate pesticide runoff into surface waters. The model has been coupled into current USA and EU long-term (20 to 30 yr), higher-tier regulatory pesticide EAs to estimate potential pesticide load reductions by the VFS before entering the aquatic environment. A new comprehensive modeling component has been added to VFSMOD to quantify the fate of pesticides residue on the VFS between events in the context of long-term simulations. The aim of this study is to present the verification of the assumptions and accuracy of the new pesticide residue component within VFSMOD in the context of continuous simulations by exploring a wide range of conditions (Koc, half-life, remobilization processes) of importance to improve current understanding of quantitative mitigation of pesticides in the regulatory environment.  The results show the complex interaction in the VFS amongst surface pesticide runoff, sedimentation, infiltration and leaching, degradation, evapotranspiration and soil moisture change, and mixing layer remobilization that produces emergent behavior in the amount of pesticide residue potentially remobilized in the next event in the series.