PERSISTENCE AND BIODEGRADATION OF DIAZINON IN SUBMERGED SOILS

Only 2 to 6% of the originally applied diazinon [O,O-diethyl O-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate] remained in the soils between 50 and 70 days after application when added to three submerged tropical soils at a rate about seven times that recommended for protecting rice plants from stem borer infestation and certain virus-transmitting leaf hoppers. Losses of the insecticide from sterilized samples of two of the soils were much slower than from nonsterilized samples, indicating microbial participation in diazinon degradation in these two soils. Diazinon disappeared rapidly in sterilized samples of the third soil, an acid clay of pH 4.7, apparently because of its instability under acid conditions. Microbial degradation of the pyrimidine ring of the diazinon molecule was demonstrated by the release of Cl4O2 from submerged soils treated with diazinon labeled at the 2 position of the pyrimidine ring. Streptomyces sp. isolated from diazion-treated submerged soil could degrade diazinon in shake cultures, but only in the presence of glucose. © 1969, American Chemical Society. All rights reserved.