Metabolism of Diazinon and Zinophos in Soils1

The identity and persistence of degradation compounds associated with the decomposition of C14 ring-labeled diazinon and Zinophos® (O, O-diethyl O-2-pyrazinyl phosphorothioate) were determined in a silt loam by thiner and gas-liquid chromatography. A primary degradative pathway of the insecticides is hydrolysis at the heterocyclic phosphate bond, followed by disruption of the cyclic moiety with subsequent formation of C14O2. After 20 weeks at 25°C, 10 to 15% of the insecticides remained. Of the C14 from diazinon and Zinophos, 35 and 60% respectively, were evolved as C14O2. A radioactive hydrolysis product, 2-isopropyl-4-methyl-6-hydroxy-pyrimidine was extracted from soil treated with diazinon, but 2-pyrazinol, the expected hydrolysis product of Zinophos, was not identified positively in non-sterile soil. Greater amounts of the hydrolysis compounds were recovered from fumigated soil in which the microbial activity was reduced, than from non-fumigated soil. Conversely, little C14O2. was released from the fumigated soil. The oxygen analogs of diazinon and Zinophos were not detected in soil treated with the parent compounds.