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

Abstract

A mathematical screening mode! 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, r. 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 sitespecific 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. Additional index words: Screening model, Chemical transport, Leaching. Jury, W.A., D.D. Focht, and W.J. Farmer. 1987. Evaluation of pesticide groundwater pollution potential from standard indices of soil-chemical adsorption and biodegradation. J. Environ. Qual. 16:422-428. 422

Adsorption of atrazine and phosphate as affected by soil depth in allophanic and non‐allophanic soils

“…Adsorption-desorption studies not only help predict the extent of leaching and redistribution of herbicides, but also help quantify the amount of herbicide required for effective weed control in soils. For an assessment of mobility and pollution potential of pesticides, the sorption or partition coefficient (K d ) and the degradation half-life (t1 /2 ) are needed (Jury et al 1986). Both these parameters are generally considered to be largely determined by the organic carbon content of the soil, especially in the case of organic pesticides and hydrocarbons (Johnson & Sims 1993;Bolan & Baskaran 1996a).…”

Screening Method for Assessing Pesticide Leaching Potential

“…The pesticide sorption is treated as an instantaneous, reversible, and linear process, thus the sorbed phase concentration (S) in soils can be related to the dissolved phase concentration (C) by the following: [11] From the Equation 1, the pesticide degradation can be estimate considering the convection time: [12] The pesticide property taken into account in the retardation factor calculation is Koc, and according to JURY et al (12), it appears to be a useful benchmark property for characterizing susceptibility to leaching for compounds that move primarily in the liquid phase. Thus, it can be used…”

“…Some have attempted to set threshold values for a physical property or set of properties which, when exceeded, should indicate that the pesticide will leach (1,16). Others have proposed very simple analytical or numerical models which are run using the measured or estimated properties of the pesticide and soil, in order to predict the likelihood of leaching (3,6,7,11,14). Clearly, any method of assessing leachability must account for both the persistence and the mobility of the chemical.…”

Retention behavior of hydrophobic organic chemicals as a function of temperature in soil leaching column chromatography

“…Industrial discharges of organic chemicals and application of agrochemicals to the crop field have become two primary routes for groundwater contamination (Jury et al, 1987;Teso et al, 1996). Improving our knowledge about the mechanism that dominates the transport of hydrophobic organic chemicals (HOCs) is essential for the understanding of pollution processes and the developing of efficient prevention and remediation strategies.…”