Adsorption and mobility of acephate in soils.

The influence of soil properties on the adsorption and mobility of acephate (O, S-dimethylacetylphosphoroamidothioate) was studied. The Freundlich adsorption constant (K) and the distribution coefficient (Kd) were found to be highly correlated (P < 0.001) with the silt + clay content of the soil, both for the studied soils as a whole and for those with organic matter contents below 2%. The mobility of acephate as determined by thin-layer chromatography (saturated flow conditions) was found to be Rf = 1 for all soils except the three with a high silt + clay content, whose Rf was smaller than unity. A study of the acephate mobility in soil-packed columns under unsaturated flow conditions revealed that the highest proportion of the insecticide was retained at the top of the columns; also, the insecticide distribution in the columns and the overall amounts retained and leached were related to the silt+clay content of the soils.