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Temperature and water effect on the adsorption of parathion (O, O‐diethyl O‐p‐nitrophenyl phosphorothioate) by soils was studied using 14C‐tagged parathion. The parathion was applied in aqueous solutions and in hexane over a concentration range of 1–10µg/ml. It was found that the parathion is adsorbed by soils from aqueous solution without any appreciable thermic effect. In a dry soil‐hexane‐parathion system the slightly polar parathion molecules efficiently compete with the apolar hexane molecules for adsorption sites. In hydrated soil‐hexane‐parathion systems there was no parathion adsorption. Generally as the soil water content increases, parathion adsorption decreases. The water‐temperature composite effect in a soil‐hexane‐parathion system was also studied. The rise of temperature in the soilhydrated parathion‐hexane system favors the endothermic process of water desorption, resulting in greater free adsorption sites, and consequently, in increasing parathion adsorption.

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