Nature and bioavailability of nonextractable (bound) residues in stored wheat treated with chlorpyrifos-methyl.
1993
Singh K. | Khan S.U. | Akhtar M.H. | Kacew S. | White N.D.G.
Wheat treated with chlorpyrifos-methyl [O,O-dimethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate] and stored for 28 months at 20 degrees C contained about 70% of the applied insecticide as nonextractable (bound) residue mainly in the form of parent compound. The stored wheat containing bound chlorpyrifos-methyl was fed to rats. The bound residue in wheat was released and metabolized predominantly by hydrolysis, as indicated by the presence of a major metabolite, 3,5,6-trichloro-2-pyridinol, in urine and feces. The major route of elimination was via urine, which contained 3,5,6-trichloro-2-pyridinol and O-methyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate. The acetone-extractable portion of feces contained both chlorpyrifos-methyl and 3,5,6-trichloro-2-pyridinol, whereas the nonextractable portion of feces contained only chlorpyrifos-methyl. The results show that bound residues of chlorpyrifos-methyl in stored wheat, which cannot be extracted by methods commonly used in residue analysis of grain, are highly bioavailable.
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