Factors influencing transformation rates and formation of products of phenylurea herbicides in soil

Transformation rates of phenylurea herbicides and their products were measu red in native soil, sterile soil, soil suspensions, and soil inoculated wit h pure cultures of microorganisms. In native soil, transformation rates gen erally increased with decreasing adsorption of the herbicides, but correlat ions with adsorption coefficients were poor. In sterile soil, substitution patterns of the compounds influenced transformation rates. In soil suspensi ons, transformation rates increased with lipophilicity of the herbicides. I n sterilized soil inoculated with specific microorganisms, transformation w as mainly influenced by substrate specificities of the microorganisms to re active sites of the phenylureas. In all cases, N-demethylation was an impor tant, but not the only, transformation pathway. The data indicate that tran sformation rates of phenylureas in soils are affected by several parameters , related to the soil, the compounds, and the type of transformation. Altho ugh the results were gained in the laboratory under artificial conditions, they form a basis to establish quantitative structure-reactivity relationsh ips and provide explanations for quality and quantity of the formed product s.