THE MOBILITY OF SOME ORGANOPHOSPHORUS PESTICIDES IN SOILS AS AFFECTED BY SOME SOIL PARAMETERS

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Abstract
Using soil thin layer chromatography (soil TLC), we conducted laboratory experiments to evaluate the mobility (R1) of four organophosphorus pesticides—dimethoate, malathion, phosphamidon, and dich-lorvos—in soils. The effects of soil organic matter (SOM) and fractions, i.e., humic (HA) and fulvic acids (FA), clay content, sesquioxides (A12O3 and Fe2O3), soil pH, and exchangeable cations and anions were investigated. We observed that, except for sakit sandy loam soil, the mobility of these pesticides followed the order: dimethoate ≥ phosphamidon > malathion > dichlorvos, which was attributed to their adsorption over soil colloids. The SOM; HA; FA; clay content; sesquioxides; acidic and alakline pH; exchangeable cations, i.e., H+, K+, Ca2+ and Mg2+; and anions, i.e., CO32-, SO42-, and H2PO4- were all found to decrease the pesticide mobility in soils, except for HA, which increased the malathion and phosphamidon mobility. However, the C1- caused an increase in the mobility of all the pesticides. The order of exchangeable cations to affect the mobility was: H+ > CA2+ > Mg2+ > K+. The results have been explained on the basis of their adsorption/complexation, the nature of soil colloids, and the molecular structure of pesticides. © Williams & Wilkins 1986. All Rights Reserved.