Adsorption of disulfoton by soil

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Abstract
Adsorption of the systemic insecticide disulfoton (diethyl S‐[2‐(ethylthio) ethyl] phosphorothiolothionate) by soil was studied using a wet slurry technique. Extraction of soils and solutions after equilibration showed that more disulfoton was lost from solution than could be extracted from soil, principally because of microbial alteration and adsorption by glass. In two contrasting soils equilibration was complete by 3 h and air‐dry soils in the laboratory adsorbed similarly to the moist field soils from which they were derived. Adsorption was fully reversible if desorption took place immediately after uptake when soils were still wet, but the release was modified when the soils were allowed to dry thoroughly between adsorption and desorption. The empirical Freundlich isotherm fitted adsorption results for 17 different soils well. The isotherms had different curvatures but deviations from linearity were small so that linear isotherms provide good approximations. Comparison of the slopes of the best‐fitting linear relationships showed that adsorption was closely related to the amount of organic matter in the soil.