Retention of Three Insecticides on Different Size Soil Particles Suspended in Water

Studies were made to determine the retention of DDT, endosulfan and methoxychlor on different sized soil particles. The two soils used were Marshall silt loam from Iowa and Caribou silt loam from Maine. A portion of each soil was treated with H2O2 to study the effect of organic matter on pesticide retention. Retention of DDT and methoxychlor was highest in the clay fraction of both treated and untreated soils. In the untreated soils the greatest retention of the three insecticides was on the colloidal (<0.08 µ) and 0.08–0.5 µ fraction. Removing the organic matter from both soils reduced the retention on the <0.08 µ and 0.08–0.5 µ clay fractions. The two soils reacted differently to the H2O2 treatment, although the three insecticides followed very similar trends within a soil. It appears that although organic matter contributes to the retention of the insecticides studied, other soil properties also are responsible for adsorption.