Parathion reduction

Reduction of Nitro Substituents. These reactions are very common in anaerobic environments and result in amine-substituted pesticides anaerobic bacteria capable of reducing nitrate to ammonia appear to be primarily responsible. All nitro-substituted pesticides appear to be susceptible to this transformation, eg, methyl parathion (7) (eq. 9), triduralin, and pendimethalin. 

Hematological Effects. No information was found regarding hematological effects in humans following exposure to methyl parathion. Repeated oral exposure to methyl parathion resulted in decreased mean corpuseular volume in one study and decreased hematocrit and erythrocyte count in another study in rats. Chronic ingestion of methyl parathion induced reduction of mean hemoglobin, hematocrit, and erythrocyte eounts in rats. 

A dose-response relationship was noted in dogs exposed to 0.03, 0.3, or 3.0 mg/kg/day methyl parathion in the diet for 13 weeks (Daly 1989). Significant reductions in erythrocyte cholinesterase activity (20-23%) and cholinesterase activity in the pons and cerebellum of the brain (43-54%) occurred in dogs... 

Clark GJ, Goodin RR, Smiley JW. 1985. Comparison of ultraviolet and reductive amperometric detection for determination of ethyl and methyl parathion in green vegetables and surface water using high-performance liquid chromatography. Anal Chem 57 2223-2228. 

For spray residues of parathion Averell and Norris (4) have developed a method that is sensitive to about 20 micrograms. The method is based on the reduction of the nitro... 

Reduction of Parathion. This reduction is carried out in the same kind of bottle and in the same bath as shown in Figure 7. Such a tall bottle, in contrast to a beaker or short flask, maintains reflux conditions and thus prevents excessive losses of alcohol. As indicated by Averell and Norris (1) and verified by the authors, this procedure will reduce quantitatively several milligrams of parathion in the time specified. Ordinarily six reductions are carried on simultaneously. 

The first compound of Equation 36 is not made by the condensation procedure, but by the chemical reduction of a nitro group in parathion. Some compounds are rather difficult to obtain by the general method. However, the next three compounds shown here were prepared by this method. 

Averell and Norris (3) have developed an analytical method adapted to the determination of parathion in spray or dust residues, which is sensitive to about 20 micrograms. It is based upon the reduction of parathion with zinc to the amino compound, diazotiza-tion, and coupling with Bratton and Marshall s amine, which gives an intense magenta color with an absorption peak at 555 millimicrons. Bowen and Edwards (6) have used the polarograph to assay technical grades of parathion and its formulations. 

The pure compound is a pale yellow, nearly odourless oil, soluble in organic solvents, but almost insoluble in water. Averell and Norris2 describe the detection of minute quantities of parathion (20 /ig.) in spray and dust, by reduction with zinc, diazotization and coupling with an amine to give an intense magenta colour. It is effective (at concentrations of 25-600 p.p.m.) against many insect species, but of course, like the majority of organo-phosphorus insecticides, it is toxic to man and to animals. 

A spectrophotometric determination of parathion-methyl (258) in soil and various vegetables is based on reduction of the nitro group to an amino group with zinc/HCl, dia-zotization and coupling with guaiacol (259) to form a yellow-colored azo dye in alkaline medium532. 

Such reductions may result in loss or diminution of the harmful effects as microorganisms convert the broad-spectrum poison 2,4-dinitrophenol to 2-amino-4-and 4-amino-2-nitrophenol, the fungicide pentachloronitrobenzene to penta-chloroaniline, and the insecticide Parathion to aminoparathion. 

The hydration status of the clay or earth material may affect the adsorption capacity of nonpolar (or slightly polar) toxic chemicals. Continuing with parathion as a case study, Fig. 8.33 shows the increase adsorbed parathion on attapulgite from a hexane solution, as the adsorbed water on the clay surface decreases. This behavior may be explained by the competition for adsorption sites between the polar water and the slightly polar parathion. Possibly, however, the reduction in adsorption due to the presence of water is caused by the increased time required for parathion molecules to diffuse through the water film to the adsorption sites. 

Degradation of parathion in soil was by hydrolysis to p-nitro-phenol and diethylthiophosphoric acid and reduction to aminopara-thion (25,26). Chemical oxidation of parathion in soils and waters was not prevalent, although oxidation of the phosphorus-sulfur bond has been shown to occur under ultraviolet light and in oxidizing environments (26). At ordinary levels of application to soil, parathion was degraded within weeks if microbial activity was available (27). Accumulations even after repeated applications were unlikely (28). When higher concentrations were applied to soil, persistence increased. Simulated spills of concentrated parathion resulted in a 15% residue after five years (29) and 0.1% after 16 years (30). 

A cotton farm in Narrabri, New South Wales, was contaminated with irrigation runoff. The 80,000-liter holding pond was treated with a free form of the Orica enzyme. A 90% reduction in methyl parathion was affected within 10 minutes. The final concentration decreased to 0.4 ppb after 1 hour from an initial concentration of 7 ppb. ... 

Reductive reactions, like oxidation, are carried out at different rates by enzyme preparations from different species. Microsomes from mammalian liver are 18 times or more higher in azoreductase activity and more than 20 times higher in nitroreductase activity than those from fish liver. Although relatively inactive in nitroreductase, fish can reduce the nitro group of parathion, suggesting multiple forms of reductase enzymes. 

Reduction of aromatic nitro groups occurs in three steps, via nitroso and hydroxylamine intermediates, to the amine. The amine can go on to form polymeric residues by a mechanism analogous to that for oxidative coupling of phenols, as in Equation 2. Abiotic nitro reduction is well documented for pesticides that contain aromatic nitro groups, such as the phosphorothioate esters methyl and ethyl parathion (22, 30-33). 

The ELISA procedure for the analysis of parathion as described above requires nearly eight hours, although many samples can be simultaneously assayed. However, incubation times can be shortened to one-half hour, in most cases, resulting in only a 10% reduction in sensitivity. Also the polystyrene microtiter plates containing bound RSA-AP can be mass produced and stored in a freezer. Since the enzyme-linked antibody can be purchased, the limiting factor of the applicability of the ELISA procedure, as well as the RIA procedures, for other pesticides is the development of the antiserum to the pesticide. 

The major metabolic route for 2-nitrophenol and 4-nitrophenol is conjugation, with the resultant formation of either glucuronide or sulfate conjugates. Conjugates are more polar than the parent compounds and, therefore, are easier to excrete in the urine. Other possible routes of metabolism include reduction to amino compounds or oxidation to dihydric nitrophenols (catechols). In humans, the evidence is indirect and comes from studies of exposure to the pesticide parathion, of which 4-nitrophenol is a metabolite (Fatiadi 1984). 

Epoxidation and hydroxylation A-Dealkylation O-Dealkylation -Dealkylation -Oxidation A-Oxidation P-Oxidation Desulfuration Dehalogenation Nitro reduction Azo reduction Cytochrome P450 (CYP) Aflatoxin, aldrin, benzo[a]pyrene, bromobenzene, naphthalene Ethylmorphine, atrazine, dimethylnitrocarbamate, dimethylaniline p-Nitroanisole, chlorfenvinphos, codeine Methylmercaptan Thiobenzamide, phorate, endosulfan, methiocarb, chlorpromazine 2-Acetylaminofluorene Diethylphenylphosphine Parathion, fonofos, carbon disulfide CCLt, CllCb Nitrobenzene O-Aminoazotoluene Flavin-Containing Monooxygenase (FMO)... 

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