Comparison of two pesticide leaching indices

Agriculture is the leading cause of regional-scale nonpoint source (NPS) po llution in the world today. Indices of pesticide leaching in the vadose zon e are well suited for estimating the spatial accumulation and distribution of NPS pollutants in the near surface. In this study the Attenuation Factor (AF) and the Leaching index (Li) are used to assess the near-surface leach ing potential for 32 important agrochemicals for world average agricultural soil properties and recharge rates. The AF and Li indices both require the same input data and appear to work well for nonpolar chemicals. In the eff ort reported here the AF and Li indices produced similar results for the 32 agrochemicals. Pesticides with high and moderate leaching potential are id entified. The AF estimates were more constant than the Li estimates for cha nges in the compliance depth and recharge rate. The AF index is simpler to use than the Li index and, therefore, is more likely to be employed in the future for screening/ranking agrochemicals relative to regional-scale NPS g round water vulnerability.