Diazinon biotransformation

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. 

Diazinon is rapidly biotransformed and excreted in mammals. Estimated half-times of diazinon persistence were 6 to 12 h in rats (Anonymous 1972) and dogs (Iverson et al. 1975). Most of the diazinon metabolites were excreted in the urine as diethyl phosphoric add and diethyl phosphorothioic acid in dogs (Iverson et al. 1975), and as hydroxy diazinon and dehydrodiazinon in sheep (Machin et al. 1974). 

Keizer, J., G. D Agostino, and L. Vittozzi. 1991. The importance of biotransformation in the toxicity of xenobiotics to fish. I. Toxicity and bioaccumulation of diazinon in guppy (Poecilia reticulata) and zebra fish (Brachydanio rerio). Aquat. Toxicol. 21 239-254. 

The magnitude of diazinon toxicity, like the toxicity of any xenobiotic, is affected by the rate of its metabolic biotransformation to both more and less toxic substances (Klaassen et al. 1986). Therefore, low xenobiotic metabolizing activity could result in greater toxicity. The newborn of several animal species, including humans, have a reduced ability to metabolize xenobiotics and may be more sensitive to diazinon toxicity. 

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