PHOTOLYSIS OF ORGANOPHOSPHORUS INSECTICIDES ON SOIL SURFACES

Photolysis on soil surfaces of the organophosphorus insecticides diazinon, methidathion and profenofos was studied under artificial sunlight conditions. All three compounds were readily degraded under the conditions used. The rate of degradation decreased in the order diazinon, profenofos, methidathion and was always greater in moist than in dry soil. The same order of stability was also observed from photolysis studies in aqueous solution. The major photolysis products identified were 2‐isopropyl‐6‐methylpyrimidin‐4‐ol from diazinon, 5‐methoxy‐3H‐1,3,4‐thiadiazol‐2‐one from methidathion and 4‐bromo‐2‐chlorophenol and 4‐bromo‐2‐chlorophenyl ethyl hydrogen phosphate from profenofos. The same compounds were formed in hydrolysis studies and also upon photodecomposition in aqueous solutions of diazinon and methidathion. Profenofos, however, showed a different photolytic reaction in aqueous systems, forming O‐(2‐chlorophenyl) O‐ethyl S‐propyl phosphorothioate. Soil photolysis studies together with hydrolysis experiments could be a useful quick method for obtaining early information on the chemical breakdown products which are to be expected in the soil environment. Copyright © 1979 John Wiley & Sons, Ltd