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Chemical Conversion of Parathion on Soil Surfaces¹

ABSTRACT

Chemical conversion of parathion was studied on a range of sterile soils widely different in organic matter content and clay mineralogy. After 130 days' incubation at room temperature, conversion ranged between 3–23% for air-dried samples and was < 10% for moist ones in all the soils studied. The conversion was found to proceed via hydrolysis of the phosphate ester bond. A conversion mechanism is proposed. The conversion was affected by soil constituents like clay and organic matter—the rate decreasing in the order:—kaolinite > montmorillonite > organic matter, this being inversely related to the adsorption affinity of these materials for parathion. This phenomenon is explained by assuming that surface catalysis of parathion occurs at specific active sites only. For almost all the soils studied, the presence of water apparently blocked the active sites required for parathion decomposition, indicating that the soils' catalytic activity is moisture dependent.

¹ Contribution from the Agricultural Research Organization, Volcani Center, Bet Dagan, Israel. 1975 Series no. 123-E. This research has been financed in part by a grant made by the National Council of Research and Development.

² Head, Division of Soil Residues Chemistry, Institute of Soils & Water, Agric. Research Organization, The Volcani Center, Bet Dagan, Israel.

Received for publication July 5, 1974. Accepted for publication March 6, 1975.