Evaluation of Pesticide Groundwater Pollution Potential from Standard Indices of Soil‐Chemical Adsorption and Biodegradation

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Abstract
A mathematical screening model of the pesticide leaching process is used to estimate the potential for a pesticide to reach groundwater at significant concentrations. The model assumes steady water flow, equilibrium linear adsorption, and depth‐dependent first‐order biodegradation and predicts groundwater travel times and residual concentrations that depend on soil and environmental conditions as well as pesticide adsorption and decay constants. When groundwater protection is expressed as a condition that the residual undegraded pesticide mass remaining below the surface layer of soil must be less than a specified fraction of the initial mass added in a pulse application at the surface, the model prediction is shown to reduce to a linear inequality between the organic C partition coefficient Koc and the biochemical half‐life, τ. The screening model is illustrated on 50 pesticides and two scenarios representing low and high potential for groundwater contamination. The calculations reveal a significant dependence on site‐specific soil and environmental conditions, suggesting that regulations restricting pesticide use should take soil and management factors as well as chemical properties into account when screening for groundwater pollution potential.