Dichlorvos hydrolysis

Slowly hydrolyzes in water and in acidic media but is more rapidly hydrolyzed under alkaline conditions to dimethyl hydrogen phosphate and dichloroacetaldehyde (Capel et al., 1988 Hartley and Kidd, 1987 Worthing and Hance, 1991). In the Rhine River (pH 7.4), the hydrolysis half-life of dichlorvos was 6 h (Capel et al, 1988). 

Following oral administration to animals, dichlorvos is rapidly absorbed from the digestive tract and extensively metabolized in the liver. The metabolism of dichlorvos has not been clearly elucidated because almost none of its potential metabolites has been yet unequivocally identified due mainly to its very rapid biotransformation rate (6). It appears, however, that the initial hydrolysis of dichlorvos, which occurs in all species, leads presumably to dichloroacetaldehyde (40), which is further metabolized by reduction to dichloroethanol or oxidation to dichloroacetic acid. In addition, dealkylation to desmethyldichlorvos appears to be another minor route of biotransformation, except in the mouse where desmethyldichlorvos constitutes at least 18% of the administered radioactivity. The metabolites of dichlorvos do not persist in tissues, whereas only trace levels occur in the milk of lactating mammals (41). There is no evidence tliat the metabolites of dichlorvos are toxic. 

In general, it is not absorbed from the soil by plants. Dichlorvos undergoes hydrolysis and biodegradation. Soil pH influences dichlorvos degradation. 

Dichlorvos adsorbs very poorly to soil particles and is soluble in water, in which it degrades primarily by hydrolysis, with a half-life of 4 days in lakes and rivers. 

Bluegill and catfish were both able to hydrolyze DFP, dichlorvos, and dimethyl 2,2,2-trichloro-l-n-butyryloxyethyl phosphonate (butonate). Catfish enzymes were also able to hydrolyze paraoxon and methyl 3-hydroxy-alpha-cronate dimethyl phosphate (mevinphos) although at a very slow rate. Kms calculated for the enzymes of both species indicated that each had a greater affinity for DFP than dichorvos. Sulfhydryl reagents and Cu2+ were found to inhibit the enzymatic activity of both organisms. Paraoxon had no effect. Cleavage products were identified as dimethyl phosphate and 2,2-dichloroacetaldehyde from dichlorovos hydrolysis and diisopropyl phosphate from the hydrolysis of DFP. 

Many organophosphorus insecticides with aliphatic leaving groups have been developed. We shall describe trichlorfon, dichlorvos, dimethoate, and malathion. Trichlorfon has to be activated to dichlorvos by an intramolecular rearrangement combined with hydrolysis ... 

Most OPPs are slightly water-soluble, have a high and a low vapor pressure. Some are very miscible with water (trichlorfon, vamidothion, mevinphos, monocrotophos, omethoate, oxydeme-ton-methyl, phosphamidon). Most, with the exception of dichlorvos, are of comparatively low volatility, and are all degraded by hydrolysis, yielding water-soluble products. Parathion, for example, is freely soluble in alcohol, esters, ethers, ketones, and aromatic hydrocarbons, but is almost insoluble in water (20 ppm), petroleum ether, kerosene, and spray oils. 

A large water-soluble Fe4Lg caging ligand 598 (Scheme 6.21) is reported [36] to catalytically accelerate the hydrolysis of acetylcholine esterase inhibitors, such as insecticide dichlorvos (see Sect. 4.1.1). 

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