Potential of the insecticides acephate and methamidophos to contaminate groundwater

The possible contamination of groundwater by the insecticides acephate and methamidophos was assessed using the behavior assessment model (BAM) and th e groundwater pollution-potential model (GWP). The dissipation coefficients of the two insecticides in two soils (Annei silt loam and Pingchen silt cl ay loam) at different moisture contents (50 and 100% field capacity) and so il temperatures (20 and 30 degrees C) were studied by determining the degra dation and adsorption of each insecticide in the soil. The movement of acep hate and methamidophos was studied by leaching each insecticide in a soil c olumn in the laboratory. The absorption coefficient of methamidophos was mu ch higher than that of acephate in both types of soil. In the leaching test , methamidophos more easily leached out from the Pingchen soil column than from the Annei soil column. Methamidophos was rapidly degraded, with a half -life of 1.11 to 1.61 days in the Annei soil and 7.50 to 13.20 days in the Pingchen soil at different temperatures and soil water contents. Acephate w as found to have a longer half-life than methamidophos in soil; however, th e mobility of methamidophos in both soils was slower than that of acephate, The mobility of acephate in soil is somewhat faster than that of methamido phos, and thus acephate may lead to the contamination of groundwater much m ore easily than methamidophos under normal conditions. (C) 2000 Academic Pr ess.