Methamidophos

Lonsway JA, Byers ME, Dowla HA, et al. 1997. Dermal and respiratory exposure of mixers/sprayers to acephate, methamidophos, and endosulfan during tobacco production. Bull Environ Contam Toxicol 59(2) 179-186. 

A few OP compounds cause delayed neuropathy in vertebrates because they inhibit another esterase located in the nervous system, which has been termed neuropathy target esterase (NTE). This enzyme is described in Chapter 10, Section 10.2.4. OPs that cause delayed neuropathy include diisopropyl phosphofluoridate (DFP), mipafox, leptophos, methamidophos, and triorthocresol phosphate. The delay in the appearance of neurotoxic symptoms following exposure is associated with the aging process. In most cases, nerve degeneration is not seen with initial inhibition of the esterase but appears some 2-3 weeks after commencement of exposure, as the inhibited enzyme undergoes aging (see Section 16.4.1). The condition is described as OP-induced delayed neuropathy (OPIDN). 

Kicuchi and Saito used carbon Empore disks in combination with SDB-XD Em-pore disks to extract polar (methamidophos, acephate and trichlorfon) and nonpolar pesticides (diazinon, chloroneb and simazine) from water. The water sample (500 mL) was passed through the disk and the disk simultaneously eluted with 30 mL of acetone-ethyl acetate (1 1). The samples were concentrated and analyzed by GLC/MS. 

Results may confirm the need for novel policy interventions to more fairly divide the risk reduction burden between US farmers and those growing crops for export to the USA. Recent trends in methamidophos residues in a variety of Mexican produce imported into the USA are particularly worrying, especially in contrast to the solid progress made by US growers in reducing the frequency and mean levels of methamidophos residues in the same foods. 

P.R.B. de O Marques, G.S. Nunes, T.C.R. dos Santos, S. Andreescu, and J.L. Marty, Comparative investigation between acetylcholinesterase obtained from commercial sources and genetically modified Drosophila melanogaster application in amperometric biosensors for methamidophos pesticide detection. Biosens. Bioelectron. 20, 825-832 (2004). 

Szeto et al. [97] have described a simple gas chromatographic method for the determination of Acephate and Methamidophos residues in sediments. 

Pathway a in Fig. 9.15 is one of amide hydrolysis mediated by a carboxy-amidase. The metabolite thus produced is methamidophos, the toxic species formed predominantly in insects and far less in mammals. Pathways b and c lead to an O-demethyl and a demethylthio metabolite, respectively. The re-... 

Fig. 9.15. Metabolism of acephate (9.82) in mammals [156]. Pathway a leads to toxification by producing methamidophos. Pathways b-d are reactions of detoxification that lead to an O-demethyl, a demethylthio, and a deacetylamino metabolite, respectively.

M. Mahajna, G. B. Quistad, J. E. Casida, Acephate Insecticide Toxicity Safety Conferred by Inhibition of the Bioactivating Carboxyamidase by the Metabolite Methamidophos , Chem. Res. Toxicol. 1997, 10, 64-67. 

Methamidophos, see Acephate Methane, see Acetaldehyde, Benzoic acid, 7 Bromobenzoic acid. 3-Bromobenzoic acid. 4-Bromobenzoic acid. Bromoform, Carbatyl, Catechol, 2-Chlorobenzoic acid. 3-Chlorobenzoic acid. Chloroform, Dibromochloromethane, 2,5-Dichlorobenzoic acid. 1,2-Dichloroethane, Ethylamine, Ethyl bromide. Ethylene dibromide, Ethylenimine, Formic acid, Hydroqninone, 4 Hvdroxvbenzoic acid. Indole, 2-Iodobenzoic acid. 3 lodobenzoic acid. Methyl bromide, 4-Iodobenzoic acid. 2-Methylphenol, 4-Methylphenol, Phenol, Prorocatechuic acid. Svringic acid. Svringaldehvde. TCDD, Tetrachloroethylene, Toluene, Trichloroethylene, Vanillin. Vanillic acid. Vinyl chloride... 

CASRN 30560-19-1 molecular formula C4H10NO3PS FW 183.16 Soil. lu aerobic aud auaerobic soils, methamidophos aud carbou dioxide were ideutified as major soil metabolites (Hartley aud Kidd, 1987). The estimated half-life iu soil is 3 d (Wauchope, 1988). 

Nigg, H.N., Reinert, J.A., and Stamper, J.H. Disappearance of acephate, methamidophos, and malathion from citrus foliage. Bull. Environ. Contam. Toxicol., 26(2) 267-272, 1981. 

As in the case of the methyIcarhamate esters, the organophos-phorus insecticide methamidophos (0, -dimethyl phosphoramidothi-oate) may be derivatized by substitution of a hydrogen atom on the phosphoramido nitrogen atom. An outstanding example of the benefit from this type of substitution is found in acephate, the... 

The reaction between a phosphoramidothioate and N-chlorosulfenylcarbamate described in Figure 2 has been applied to methamidophos. In Figure 2, the reaction was used to derivatize a toxic me thyIcarhamate ester by a non-toxic phosphora-midothioate however, in the case of methamidophos the reaction was used to derivatize a toxic phosphoramidothioate with a nontoxic carbamate moiety. The IJ-alkoxycarbonyl-IJ -alkylamino-sulfenyl derivatives of methamidophos thus prepared, where R... 

Attempts to react methamidophos with the corresponding chlorosulfinylcarbamate intermediate, however, resulted in products which were unstable and of no value as proinsecticides. In general, phosphoramidothioates such as methamidophos are more difficult to derivatize than the methylcarbamate esters and therefore are less useful as precursors to proinsecticides. 

---