Degradation of chlorpyrifos and its hydrolysis product, 3,5,6-trichloro-2-pyridinol, in soil

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Abstract
The degradation of 14C‐chlorpyrifos and its hydrolysis product, 3,5,6‐trichloro‐2‐pyridinol (TCP), was investigated in soil in laboratory experiments. Between 12 and 57% of the applied chlorpyrifos persisted in a variety of agricultural soils after a 4‐week incubation. Concentrations of TCP present in these soils ranged from 1 to 34% of the applied dose. Two patterns of persistence were observed. In some soils, significant quantities of TCP and soil‐bound residues were produced, but little 14CO2. In other soils, neither TCP nor soil‐bound residues accumulated, but large quantities of 14CO2 were evolved. Direct treatment of fresh samples of each of these soils with 14C‐TCP resulted in rapid mineralization of TCP to 14CO2 only in those soils in which TCP had not accumulated after chlorpyrifos treatment. The rapid mineralization of TCP in these soils was microbially mediated, but populations of soil microorganisms capable of using TCP as a sole carbon‐energy source were not detected.