Malathion degradation

In shellfish only three of the eight compounds monitored were detected feni-trothion, which was found in a mussel sample at 3.46 mg/kg, malathion, found in an oyster sample at 53.12 mg/kg, and the malathion degradation product malaoxon, which was found in one oyster and two mussel samples at concentrations between 2.53 and 4.59 mg/kg. As it can be seen in Fig. 7, positive samples (five of ten analyzed) were found in both bays and in scattered days along the period of study, with the sample showing the highest pesticide concentration (53.12 mg/kg of malathion in oysters collected from the northern bay on May 27) coinciding with the period of shellfish mortality. 

At 87 °C and pH 2.5, malathion degraded in water to malathion a-monoacid and malathion P-monoacid. From the extrapolated acid degradation constant at 27 °C, the half-life was calculated to be >4 yr (Wolfe et al., 1977a). Under alkaline conditions (pH 8 and 27 °C), malathion degraded in water to malathion monoacid, diethyl fumarate, ethyl hydrogen fumarate, and QO-dimethyl phosphorodithioic acid. At pH 8, the reported half-lives at 0, 27, and 40 °C are 40 d, 36 h, and 1 h, respectively. However, under acidic conditions, it was reported that malathion degraded into diethyl thiomalate and 0,0-dimethyl phosphorothionic acid (Wolfe et al, 1977a). 

Matsumura, F. and Boush, G.M. Malathion degradation by Ttichoderma virlde and a Pseudomonas species. Science (Washington, DC), 153(3741) 1278-1280,1966. 

Figure 13 Effect of pH and temperature on malathion degradation by hydrolysis (temperature in degrees C) degradation is faster at higher temperatures and pH values further away from 4.0 to 4.2 (from Ref. 11).

The term potentiation is then reserved for those cases where both compounds have appreciable intrinsic toxicity, such as in the case of malathion and EPN. Malathion has a low mammalian toxicity due primarily to its rapid hydrolysis by a carboxylesterase. EPN (Figure 9.6) another organophosphate insecticide, causes a dramatic increase in malathion toxicity to mammals at dose levels, which, given alone, cause essentially no inhibition of acetylcholinesterase. The increase in toxicity as a result of coadministration of these two toxicants is the result of the ability of EPN, at low concentrations, to inhibit the carboxylesterase responsible for malathion degradation. 

The Si/Al ratio has a direct relationship with the pH of the resulting solution the zeolite is dispersed in. Thus, it is important to consider the resultant pH of a reaction media as this will enhance or impede adsorption processes. The overall result shows that malathion degradation in water... 

In Figure 12.9, Osewe (2014) showed the effects of ID, 2D, and 3D orientations of zeolitic channels and cavities on the half-life of malathion degradation in waste waters [16]. 

Cotham WE Ir, Bidleman TE. 1989. Degradation of malathion, endosulfan, and fenvalerate in seawater and seawater/sediment in microcosms. 1 Agric Food Chem 37 824-828. 

Matsumura and Bousch (1966) isolated carboxy lest erase (s) enzymes from the soil fungus Trichoderma viride und a bacterium Pseudomonas sp., obtained from Ohio soil samples, that were capable of degrading malathion. Compounds identified included diethyl maleate, desmethyl malathion, carboxylesterase products, other hydrolysis products, and unidentified metabolites. The authors found that these microbial populations did not have the capability to oxidize malathion due to the absence of malaoxon. However, the major degradative pathway appeared to be desmethylation and the formation of carboxylic acid derivatives. 

Soil. In soil, malathion was degraded by Arthrobacter sp. to malathion monoacid, masphoro-dithioate. After 10 d, degradation yields in sterile and nonsterile soils were 8, 5, and 19% and 92, 94, and 81%, respectively (Walker and Stojanovic, 1974). Chen et al. (1969) reported that the microbial conversion of malathion to malathion monoacid was a result of demethylation of the 0-methyl group. Malathion was converted by unidentified microorganisms in soil to thiomalic acid, dimethyl thiophosphoric acid, and diethylthiomaleate (Konrad et al, 1969). 

Surface Water. In raw river water (pH 7.3 to 8.0), 90% degraded within 2 wk, presumably by biological activity (Eichelberger and Lichtenberg, 1971). In estuarine water, the half-life of malathion ranged from 4.4 to 4.9 d (Lacorte et al, 1995). 

Konrad, J.G., Chesters, G., and Armstrong. D.E. Soil degradation of malathion, a phosphorothioate insecticide, Soil Sci. Soc. 

Singh, A.K. and Seth, P.K. Degradation of malathion by microorganisms isolated from industrial effluents. Bull. Environ. Contam. Toxicol, 43(l) 28-35, 1989. 

Walker, W.W. Chemical and microbiological degradation of malathion and parathion in an estuarine environment, J. Environ. 

It should be noted that hydrolysis of these pesticides is expected to occur simultaneously with volatilization for the pesticides studied (Table I). Over a 7 day experiment, however, only malathion and mevlnphos would be expected to hydrolyze to a significant extent. We determined the loss rate of mevlnphos to be 0.0016 0.0002 hr l (tjj = 18 days), and of malathion to be 0.011 0.001 hr-1 (t j = 2.6 days) at 22 2°C, at pH 8.2+0.2 for a model evaporation pond by daily sampling of duplicate pesticide solu-Xlons (covered to prevent volatilization) for 7 days and plotting log concentration versus time. For both of these pesticides, then, degradation was a much more important route of pesticide loss from water than volatilization. The relatively slow loss rate of the other pesticides could not be determined in our 7 day... 

The primary design parameter to be considered in hydrolysis is the half-life of the original molecule, which is the time required to react 50% of the original compound. The half-life is generally a function of the type of molecule hydrolyzed and the temperature and pH of the reaction. Figure 13 shows the elfect of pH and temperature for the degradation of malathion by hydrolysis [11]. 

Another example of this conversion of P=S found in pesticides to P = 0 is the oxidation of malathion in the atmosphere. Malathion itself is not a HAP and has relatively low acute mammalian toxicity because it is degraded by mammalian carboxylesterases. It is effective as a pesticide because in insects, it is activated to malaoxon, an acetylcholinesterase inhibitor. However, malathion itself typically contains impurities such as isomalathion whose mammalian toxicities are greater... 

Dimethyl hydrogen phosphite is used as a flame retardant on nylon 6 fibres, as a chemical intermediate in the production of pesticides and in lubricant additives and adhesives. No data on occupational exposure levels were available. A potential source of exposure to this chemical is from its occurrence as a degradation product of the chemical intermediate trimethyl phosphite and of pesticides such as trichlorphon and malathion (lARC, 1990). 

Paris, D. F., D. L. Lewis, and N. L. Wolfe, Rates of degradation of malathion by bacteria isolated from aquatic systems , Environ. Sci. Technol., 9, 135-138 (1975). 

The OPP malathion is widely used because of its low persistence in the environment and its high insecticide activity. Pure malathion has moderate toxicity, but crude malathion and its formulations contain impurities, which are far more toxic to mammals. These impurities not only are formed during commercial production but can also develop in the grains during storage. The most toxic of these products is the oxidation product malaoxon. An isocratic HPLC method indicated the degradation of malathion in stored wheat (55) and the presence of malathion and malaoxon in maize and bean samples (56). Isomalation and malation monocarboxylic acid metabolites were also detected. 

BN Anderegg, LJ Madisen. Effect of dockage on the degradation of (l4C) Malathion in stored wheat. J Agric Food Chem 31 700-704, 1983. 

Methylphosphonic acid (MPA), a degradation product of gas chemical warfare agents, such as sarin (isopropyl methylphosphonofluoridate), soman or VX (0-ethy I -.S -2-di isopropyl am i noethvl methyl phosphonoth ioate), has been recognized selectively by an MIP chemosensor using potentiometric transduction (Table 6) [181]. The MIP preparation involved co-adsorption, in ethanol, of the methylphosphonic acid (MPA) template and octadecyltrichlorosilane, followed by silanization on the indium-tin oxide (ITO) electrode surface in the chloroform-carbon tetrachloride solution at 0 °C. Subsequently, the electrode was rinsed with chloroform to remove the template. A potential shift due to the presence of MPA was significant as compared to that due to interferants like methyl parathion, dimethoate, phosdrin, malathion, etc. The linear concentration range varied from 50 pM to 0.62 M MPA at LOD as low as 50 pM and an appreciably short response time of 50 s. 

The hydrolysis of esters by esterases and of amides by amidases constitutes one of the most common enzymatic reactions of xenobiotics in humans and other animal species. Because both the number of enzymes involved in hydrolytic attack and the number of substrates for them is large, it is not surprising to observe interspecific differences in the disposition of xenobiotics due to variations in these enzymes. In mammals the presence of carboxylesterase that hydrolyzes malathion but is generally absent in insects explains the remarkable selectivity of this insecticide. As with esters, wide differences exist between species in the rates of hydrolysis of various amides in vivo. Fluoracetamide is less toxic to mice than to the American cockroach. This is explained by the faster release of the toxic fluoroacetate in insects as compared with mice. The insecticide dimethoate is susceptible to the attack of both esterases and amidases, yielding nontoxic products. In the rat and mouse, both reactions occur, whereas sheep liver contains only the amidases and that of guinea pig only the esterase. The relative rates of these degradative enzymes in insects are very low as compared with those of mammals, however, and this correlates well with the high selectivity of dimethoate. 

Residues of malathion can be degraded to nonhazardous products using aqueous acidic potassium permanganate solution. Thus, to each 1 mL of commercial malathion solution, add 50 mL of 3 M sulfuric acid (8.5 mL of concentrated sulfuric acid added to 41.5 mL of water) and 3 g of potassium permanganate. Stir the mixture at room temperature for 5 hours. Neutralize the solution by careful addition of soda ash, and then decolorize by adding, while stirring, a saturated solution of sodium bisulfite (approximately 10 g of sodium bisulfite per 35 mL of water) until a colorless solution is formed. Wash the clear solution into the drain.5... 

Walker, W.W., Stojanovic, B J. (1973) Microbial versus chemical degradation of malathion in soil. J. Environ. Qual. 2, 229-232. Wang, T.C., Hoffman, M.E. (1991) Degradation of organophosphorus pesticides in coastal water. J. Assoc. Off. Anal. Chem. 74(5), 883-886. 

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