SORPTION, DEGRADATION, AND MINERALIZATION OF CARBARYL IN SOILS, FOR SINGLE-PESTICIDE AND MULTIPLE-PESTICIDE SYSTEMS

Sorption, degradation, and mineralization of carbaryl (l-naphthyl N-me thylcarbamate) alone and in mixtures with loro-4-ethylamino-6-isopropy lamino-1,3,5-triazine) and diuron (N'-(3,4-dichlorophenyl)-N, N-dimeth ylurea) were characterized for two topsoils and their respective subso ils, In general, differences in sorption and transformation between si ngle and multiple-pesticide systems were less than differences due to soil type and between topsoil and subsoil, For a given soil, the topso il containing more organic carbon (OC) than the subsoil exhibited a la rger value for the Freundlich sorption coefficient (K-f). Similarly, a larger value for the soil solution degradation rate coefficient (k(l) ) was obtained from topsoil than subsoil, likely due to greater microb ial activity in the topsoil, However, for all soils, sorption of carba ryl on soils considerably increased the magnitude of the degradation h alf-life (t(1/2)) for carbaryl in either single-pesticide or multiple- pesticide systems, In soils that contained <10 g kg(-1) OC content, th e effect of multiple-pesticide systems was to enhance the mineralizati on of carbaryl, This was attributed to cometabolism. This study shows that carbaryl chemodynamic parameters (K-OC and t(1/2\) values) can be used to adequately analyze the fate of carbaryl in the environment ev en when carbaryl exists in a mixture with atrazine and diuron.