EFFECTS OF SOILS AND LEAF SURFACES ON PHOTODECOMPOSITION OF [C-14) AZINPHOSMETHYL

The effects of environmental conditions on the photodecomposition of [14C]azinphosmethyl by light were investigated with glass surfaces (controls), 3 soil types and surfaces of bean and corn leaves. The insecticide was not degraded in the dark. Exposure of [14C]azinphosmethyl on glass, in soils, or on leaves to sunlight or UV-light for 8 h resulted in the degradation of the insecticide and loss of radiocarbon, most on glass surfaces and least in soils. The amounts of noninsecticidal water-soluble photoproducts due to sunlight amounted to 18.6% of the applied radiocarbon on glass surfaces, 6.5% in a sandy soil, 4.3% in a loam soil, 2.5% in a muck soil, 3.5% on corn leaves and 1.4% on bean leaves. With increasing soil moisture content increased degradation occurred with UV light, but not with sunlight. The amounts of unextractable, bound residues produced due to irradiation increased with soils of higher organic matter and with increasing moisture contents. With sunlight, N-methylbenzazimide was produced only on corn leaves, while N-methylbenzazimide sulfide (or disulfide), benzazimide and the oxygen analogue of azinphosmethyl were produced on both corn and bean leaves, but primarily on bean leaves. The insecticide was least susceptible to photodecomposition when used as a granular formulation.