Diazinon metabolism

Depuration rates of diazinon differed significantly for two species of nematodes, Panagrellus redivivus and Bursaphelenchus xylophilus (Al-Attar and Knowles 1982). Both species showed maximum uptake of radiolabeled diazinon between 6 and 12 h, and both metabolized diazinon to diazoxon and pyrimidinol. By 96 h, 95% of the diazinon in P. redivivus had been metabolized, but only 26% was transformed in B. xylophilus, again demonstrating variability in diazinon metabolism between related species. 

Iverson, F., D.L. Grant and J. Lacroix. 1975. Diazinon metabolism in the dog. Bull. Environ. Contam. Toxicol. 13 611-618. 

The fate of diazinon in submerged soil and paddy water with emphasis on its metabolism by microorganisms is reviewed. The first part of this paper deals with the fate of diazinon in submerged soil which has never been exposed to diazinon. The detailed experimental procedures and results of this phase have been reported elsewhere (2,12). The second part will center largely on enhanced diazinon metabolism in submerged soil and paddy water following repeated applications at levels and intervals recommended for rice pest control. 

Isotope studies were conducted to determine the biochemical pathway of enhanced diazinon metabolism observed in paddy water of treated fields. In these studies, diazinon labelled at 4-position on the pyrimidine ring was incubated with paddy water from diazinon-treated and untreated fields as described earlier (17). The enclosed C02-free system was utilized to measure the C02 production, and the radioactivity in the evolved C02 was assayed by liquid scintillation counting (17). Diazinon residues were analyzed by gas-liquid chromatography after extraction with hexane. The results are summarized in Figure 1. Water from treated rice fields was capable of metabolizing 4-carbon atom on the pyrimdine ring, releasing more than 66% of the added radioactivity as C02 within five days of incubation. Such rapid metabolism was not observed with water from untreated field. 

Riskallah, M. R., W. C. Dauterman and E. Hodgson. 1986b, Host plant induction of microsomal monooxygenase activity in relation to diazinon metabolism and toxicity in larvae of the tobacco budworm Heliothis virescens (F.). Pest. Biochem. Physiol. 

The organophosphorons insecticides dimethoate and diazinon are mnch more toxic to insects (e.g., housefly) than they are to the rat or other mammals. A major factor responsible for this is rapid detoxication of the active oxon forms of these insecticides by A-esterases of mammals. Insects in general appear to have no A-esterase activity or, at best, low A-esterase activity (some earlier stndies confnsed A-esterase activity with B-esterase activity) (Walker 1994b). Diazinon also shows marked selectivity between birds and mammals, which has been explained on the gronnds of rapid detoxication by A-esterase in mammals, an activity that is absent from the blood of most species of birds (see Section 23.23). The related OP insecticides pirimiphos methyl and pirimiphos ethyl show similar selectivity between birds and mammals. Pyrethroid insecticides are highly selective between insects and mammals, and this has been attributed to faster metabolic detoxication by mammals and greater sensitivity of target (Na+ channel) in insects. 

Keizer J, G d Agostino, R Nagel, F Gramenzi, L Vittozzi (1993) Comparative diazinon toxicity in guppy and zebra fish different role of oxidative metabolism. Environ Toxicol Chem 12 1243-1250. 

Examples of PLC with autoradiography detection include the published studies on labeling of l- H-PAF-aceter [25] diazinon and related compounds from plant material [26] metabolic fate of triamcinolone acetonide in laboratory animals [27] synthesis of 4-S-cysteaminyl-[U- " C]phenol antimelanoma agent [28] radiolabeled... 

Even though all OP insecticides have a common mechanism of action, differences occur among individual compounds. OP insecticides can be grouped into direct and indirect ACHE inhibitors. Direct inhibitors are effective without any metabolic modification, while indirect inhibitors require biotransformation to be effective. Moreover, some OP pesticides inhibit ACHE more than PCHE, while others do the opposite. For example, malathion, diazinon, and dichlorvos are earlier inhibitors of PCHE than of ACHE. In these cases, PCHE is a more sensitive indicator of exposure, even though it is not correlated with symptoms or signs of toxicity. 

Al-Attar, H.J. and C.O. Knowles. 1982. Diazinon uptake, metabolism, and elimination by nematodes. Arch. Environ. Contam. Toxicol. 11 669-673. 

Fujii, Y. and S. Asaka. 1982. Metabolism of diazinon and diazoxon in fish liver preparations. Bull. Environ. Contam. Toxicol. 29 453-460. 

Hogan, J.W. and C.O. Knowles. 1972. Metabolism of diazinon by fish liver microsomes. Bull. Environ, Conlam. Toxicol. 8 61-64. 

Plant Diaziuou was rapidly absorbed by and translocated in rice plants. Metabolites identified in both rice plants and a paddy soil were 2-isopropyl-4-methyl-6-hydroxypyrimidine (hydrolysis product), 2-(l -hydroxy-l -methyl)ethyl-4-methyl-6-hydroxypyrimidine, and other polar compounds (Laanio et al, 1972). Oxidizes in plants to diazoxon (Laanio et al., 1972 Ralls et al, 1966 Wolfe et al., 1976) although 2-isopropyl-4-methylpyrimidin-6-ol was identified in bean plants (Kansouh and Hopkins, 1968) and as a hydrolysis product in soil (Somasundaram et al., 1991) and water (Suffet et al., 1967). Five d after spraying, pyrimidine ring-labeled C-diazinon was oxidized to oxodiazinon which then hydrolyzed to 2-isopropyl-4-methylpyrimidin-6-ol which, in turn, was further metabolized to carbon dioxide (Ralls et al, 1966). Diazinon was transformed in field-sprayed kale plants to hydroxydiazinon 0,0-diethyl-0-[2-(2 -hydroxy-2 -propyl)-4-methyl-6-pyrimidinyl] phosphorothioate which was not previously reported (Pardue et al., 1970). 

Getzin, L.W. Metabolism of diazinon and zinophos in soils. J. Econ. Entomol, 60(2) 505-508,1967. 

Kansouh, A.S.H. and Hopkins. T.L. Diazinon absorption, translocation, and metabolism in bean plants, J. Agrlc. Food Chem., 16(3) 446-450, 1968. 

Organophosphate insecticides (e.g., malathion, parathion, diazinon) undergo metabolic activation to... 

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