China
Africa
Explore chapters and articles related to this topic
Xenobiotic Metabolism
Published in Lorris G. Cockerham, Barbara S. Shane, Basic Environmental Toxicology, 2019
Larry G. Hansen, Barbara S. Shane
The complexity of the activation and detoxification pathway of a typical organophosphate insecticide, malathion, in insects and mammals is shown in Figure 3.6, I. Cytochrome P450 enzymes activate malathion through oxidative desulfuration to form the more toxic intermediate, malaoxon (Figure 3.4, IV). In the conversion of P=S to P=0, a “phosphooxythirane” intermediate (Figure 3.6, III) is formed followed by the releases of a reactive sulfide. Malaoxon (Figure 3.6, IV) is the active intermediate that phosphorylates acetylcholinesterase. With phosphorothioates containing an aromatic leaving group in place of the mercaptosuccinate diethyl ester, the phosphooxythirane intermediate may rearrange in such a way as to cause dearylation. Detoxification of malathion by cytochrome P450 may also occur by removal of a methoxy group (I → II or IV → V).
A comprehensive review on enzymatic degradation of the organophosphate pesticide malathion in the environment
Published in Journal of Environmental Science and Health, Part C, 2019
Smita S. Kumar, Pooja Ghosh, Sandeep K. Malyan, Jyoti Sharma, Vivek Kumar
In addition to pH, temperature also governs the efficiency of malathion degradation. After heating, malathion is isomerized via a thiono-thiolo rearrangement to yield isomalathion. This reaction occurs at a very fast rate above 100 °C. Bourquin,49 while studying the fate of malathion in seawater, reported that malathion was found to be thermostable at 21 °C and underwent rapid destruction from 27 to 32 °C. The breakdown product of chemical degradation after two days was malathion monocarboxylic acid and after seven days it was malathion dicarboxylic acid. Minute quantities of malaoxon were also detected. Nadalian and coworkers isolated malathion degrading bacteria Serratia marcescens from agricultural soil and optimized the dose of ammonium chloride, salinity, temperature, and dipotassium hydrogen phosphate. In the study, the optimum temperature was found to be 30 °C.89