EFFECT OF SOIL CHARACTERISTICS ON ADSORPTION AND MOBILITY OF (C-14)DIAZINON

The adsorption and mobility of diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate) in 25 soils of different physiochemical properties were studied. The adsorption isotherms were found to conform to the Freundlich adsorption equation. Freundlich's constant, K, and the distribution coefficient, K-d, were found to be highly significantly correlated (p < 0.001) with the organic matter (OM) content when all soils or only those with an OM content above 2% were considered. There was also a significant correlation (p < 0.01) of K and K-d with the silt plus clay content of soils with an OM content below 2%. On the basis of the R(f) values obtained by TLC, the pesticide was found to be slightly mobile in 80% and immobile in 20% of the soils studied. A study of the pesticide mobility in soil columns under saturated flow conditions showed it to be leached from light soils with low OM contents.