Investigations of the determination and transformations of diazinon and malathion under environmental conditions using gas chromatography coupled with a flame ionisation detector

Degradation of two model insecticides, diazinon and malathion, and their degradation products 2-isopropyl-6-methyl-4-pyrimidinol--IMP (diazinon hydrolysis product) and malaoxon (malathion oxidation product) was compared and studied in the environment. The pesticides and their metabolites were extracted from samples (water, soil, chicory) with ethyl acetate and subsequently the extracts were analyzed by GC/FID. It was shown that hydrolysis is the major process in the degradation of these pesticides in water. In fact, 95% of diazinon was degraded, and only 10% of malathion was oxidised. In soil 30% of diazinon exposed to the sunlight was decomposed by photolysis, whereas in soil left in the darkness no degradation products were observed. In soil left under environmental conditions, 90% of diazinon was degraded and 40% from its initial concentration was transformed into IMP. The concentrations of the pesticides after 21 days on chicory were under maximal allowable concentration, which is 0.5 ppm for malathion and for diazinon. The concentration of malaoxon was more than twice as high as the allowable value, which is for the sum of malathion and malaoxon 3 ppm.