Persistence and Degradation of Azinphosmethyl in Soils, as Affected by Formulation and Mode of Application1

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Abstract
The persistence and metabolism of azinphosmethyl (Guthion®) in soils was studied under field and laboratory conditions. The insecticide was least persistent after field application in an emulsion and when left on the soil surface (50% loss within 12 days after soil treatment) and was most persistent (50% loss within 28 days) after its incorporation in granular form into the upper 4-5 inches of the soil. One year after soil treatment with azinphosmethyl granules, 13% of the applied dosage was recovered in the form of azinphosmethyl, and the derivatives mercaptomethyl benzazimide, N-methyl benzazimide and N-methyl benzazimide sulfide or N-methyl benzazimide disulfide. In addition, benzazimide plus 4 unknown compounds were detected. However, toxic effects observed with Drosophila melanogaster Meigen flies or with larvae of the yellow-fever mosquito, Aedes aegpti (L,) were due only to azinphosmethyl Nearly all the insecticide, although applied at the relative high dosage of 5 lb per acre, was degraded in 1 year into non-toxic products, and more azinphosmethyl derivatives than azinphosmethyl were present at that time. Two years after the insecticidal application, only traces of azinphosmethyl were left in the soil, and concentrations of azinphosmethyl derivatives had also declined. The amount of 14-azinphosmethyl applied to soils under laboratory conditions declined over a 10-week period, while the amounts of several nontoxic and more polar derivatives increased during that time.

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