Calculating pesticide sorption coefficients ( Kd) using selected soil properties

Pesticide soil/solution distribution coefficients ( K d values), commonly referred to as pesticide soil sorption values, are utilized in computer and decision aid models to predict soil mobility of the compounds. The values are specific for a given chemical in a given soil sample, normally taken from surface soil, a selected soil horizon, or at a specific soil depth, and are normally related to selected soil properties. Pesticide databases provide K d values for each chemical, but the values vary widely depending on the soil sample on which the chemicals were tested. We have correlated K d values reported in the literature with the reported soil properties for an assortment of pesticides in an attempt to improve the accuracy of a K d value for a specific chemical in a soil with known soil properties. Mathematical equations were developed from regression equations for the related properties. Soil properties that were correlated included organic matter content, clay mineral content, and/or soil pH, depending on the chemical properties of the pesticide. Pesticide families for which K d equations were developed for 57 pesticides include the following: Carboxy acid, amino sulfonyl acid, hydroxy acid, weakly basic compounds and nonionizable amide/anilide, carbamate, dinitroaniline, organochlorine, organophosphate, and phenylurea compounds. Mean K d values for 32 additional pesticides, many of which had K d values that were correlated with specific soil properties but for which no significant K d equations could be developed are also included.