ADSORPTION OF METHOMYL BY SOILS OF SOUTHERN SPAIN AND SOIL COMPONENTS

The adsorption of methomyl (S-methyl N-(methylcarbamoyloxy) thioacetim idate) by 14 soil samples of Southern Spain with different characteris tics has been investigated studying the correlation between adsorption and soil properties and the effect of methomyl concentration and soil /solution ratio on adsorption of methomyl by soils. Adsorption has bee n expressed as the soil-water distribution coefficient Kd. Kd values s lightly decreased when soil/solution ratio and methomyl concentration increased. These values indicated that methomyl is adsorbed weakly in soils. Kd values were compared with the soil properties by simple and multiple regression analysis. A highly significant correlation between Kd and soil organic matter and clay content was observed in every exp erimental condition. Adsorption of methomyl by clay minerals (two mont morillonites, hectorite, illite and kaolinite) and by humic acid has b een investigated as well. The higher adsorption coefficients values ob tained with humic acid indicated greater affinity of methomyl molecule s for the organic fraction of soils. Kd data obtained with clay minera ls indicate that methomyl is adsorbed not only on the external surface s of the clay minerals but also in the interlamellar space of the swel ling minerals.