Movement and adsorption of methamidophos in clay loam and sandy loam soils

Abstract

Laboratory batch and column experiments were performed to better understand the sorption and transport behaviour of commercial-grade methamidophos (Tamaron SL 600) in clay loam (CL) and sandy loam (SL) soils. The batch sorption experiments show that the soil texture and methamidophos concentration play a major role in the sorption and migration behaviour of methamidophos. At low surface coverage (q < 0.6 mg g−1), methamidophos sorbs onto the CL soil more strongly than onto the SL soil. However, for q > 0.6 mg g−1, the SL soil exhibits a much higher sorption affinity for methamidophos than the CL soil. The equilibrium isotherms for the sorption of methamidophos onto the SL and CL soils were non-linear, and were best described by the Freundlich equation. The results of column experiments indicate that the recovery of methamidophos during desorption was incomplete due to either partially irreversible sorption to high-energy surface sites or strongly rate-limited desorption. Methamidophos was more readily leached out from the SL soil column as consistent with the batch isotherm data.