Parathion hydrolysis

Serdar CM, DT Gibson, DM Munnecke, JH Lancaster (1982) Plasmid involvement in Parathion hydrolysis in Pseudomonas diminuta. Appl Environ Microbiol 44 246-249. 

Soil. A Pseudomonas sp. (ATCC 29354), isolated from parathion-amended treated soil, degraded 4-nitrophenol to 4-nitrocatechol, which was recalcitrant to degradation. In an unsterilized soil, however, p-nitrocatechol degraded to nitrites and other unidentified compounds (Sudhakar-Barik et al, 1978a). Pseudomonas sp. and Bacillus sp., isolated from a parathion-amended flooded soil, degraded 4-nitrophenol (parathion hydrolysis product) to nitrite ions (Siddaramappa et al, 1973 Sudhakar-Barik et al., 1976) and carbon dioxide (Sudhakar-Barik et al., 1976). 

Parathion hydrolysis on clay surfaces also is affected by environmental factors, such as temperature and water content. A rise in temperature generally enhances parathion hydrolysis on kaolinite, but the effect is greater in Na+-kaolinite than Ca +-kaolinite. These differences are due to the different hydrolysis pathways in the presence of Na - and Ca +- saturating cations. In the limit of sorbed water, the addition... 

Hydrolysis of parathion in a loessial semiarid soil was investigated by Nelson et al. (1982). They found that Arthrohacter sp. hydrolyzed parathion rapidly in sterilized, parathion-treated soil under aerobic conditions (20% w/w water content). This bacterium was isolated from a silty loam, sierozem soil of loessial semiarid origin (Gilat). It uses parathion or its hydrolysis product, p-nitrophenol, as the sole carbon source. However, when parathion hydrolysis causes the amount of p-nitrophenol to reach a concentration greater than 1 mM or if the concentration is greater than 1 mM in the case of a single application of p-nitrophenol, the hydrolysis product becomes noxious to the bacteria and their growth is inhibited. 

The rate of parathion hydrolysis is independent of the parathion concentration the rate of formation of the hydrolysis product, F, is described by... 

Formation of parathion hydrolysis produets in remoistened Gilat soil after applieation of parathion at eoneentrations of 10 to 160 dg dry soil is illustrated in Fig. 16.37. These data imply that parathion provides a substanee essential for the growth of a portion of the near surfaee mierobial population, but that these inereased numbers ean be sustained for only a short period. A possible explanation for the short-lived inerease in numbers, in addition to laek of substrate, might be... 

Fig. 16.37 Formation of parathion hydrolysis product (fraction of initial label appearing in the aqueous extract) in remoistened Gilat soil after application of 10-160p,g parathion per g dry soil. Plotted points are means of three replicates standard error. Continuous curves represent model simulations. Reprinted from Nelson LM, Yaron B, Nye PH (1982) Biologically-induced hydrolysis of parathion in soil. Soil Biol Biochem 14 223-227. Copyright 1982 with permission of Elsevier...

Mills and Hoffmann (1992) investigated ultrasonic degradation of parathion. Parathion (0,0-diethyl O-p-nitrophenyl triphosphate) is a major pesticide used in large quantities worldwide. Organophosphate esters such as parathion have been used as alternatives to DDT and other chlorinated hydrocarbon pesticides however, the organophosphate esters are not rapidly degraded in natural waters. At 20°C and pH 7.4, parathion has a hydrolytic half-life of 108 days and its toxic metabolite, paraoxon, has a similar half-life of 144 days. Ultrasonic irradiation of 25 mL of parathion-saturated, deionized water solution was conducted in a water-jacketed, stainless-steel cell with a Branson 200 sonifier operating at 20 kHz and 75 W/cm2. The temperature of the sonicated solution was kept constant at 30°C. All sonolytic reactions were carried out in air-saturated solution. The concentration of the parathion hydrolysis product p-nitrophenol (PNP) was determined in alkaline solution with a Shimadzu MPS-2000 UV /visible spectrophotometer. 

Serdar, C.M., Gibson, D.T., Munnecke, D.M., Lancaster, J.H. (1982). Plasmid involvement in parathion hydrolysis by Pseudomonas diminuta. Appl. Environ. Microbiol. 44 246-9. 

Ketelaar (35) reported an activation energy of 16.6 kcal mole" for parathion hydrolysis in 50% alcohol-water mixture 12V in sodium hydroxide. Ketelaar and Gersmann (36) studied the hydrolysis of parathion and paraoxon in 50% acetone-water mixture. The activation energies were reported for parathion s hydrolysis as 22.7 kcal mole" and for paraoxon as 20.5 kcal mole". The calculated activation energies for parathion and paraoxon in buffered water (Table V) are much lower than those reported by the two investigators for the mixed solvent systems. 

Methyl parathion hydrolysis has also been observed to be catalyzed by (Mabey et al., 1984). Additionally, the affected the reaction product distribution. As expected, the neutral (pH<8) hydrolysis of methyl parathion favors cleavage of the C-O bond (soft-soft interaction) (pathway a, 2.106), whereas the base-catalyzed (pH >8) hydrolysis favors cleavage of the P-O bond (hard-hard interaction (pathway b, 2.106). In the presence of Cu +, however, heterolytic cleavage of the P-O bond resulting in the formation of nitrophenol is the dominant process even at low pH (pathway b, 2.106). 

Recently this technique was applied to the evolution of OPH for increased methyl parathion hydrolysis. After two rounds of DNA shuffling, a variant that could hydrolyze methyl parathion 25-foId faster than wild type was isolated. The mutations were not directly located in the active site and could not be otherwise predicted a priori (55), This technique could be used to target other slow degrading pesticides such as chlorpyrifos and diazinon and against chemical warfare agents VX and sarin. 

Human serum paraoxonase (PON 1) is an esterase that is physically associated with high-density lipoprotein (HDL) and is also distributed in tissues such as liver, kidney, and intestine [38,39]. Activities of PON 1, which are routinely measured, include hydrolysis of organophosphates, such as paraoxon (the active metabolite of the insecticide parathion) hydrolysis of arylesters, such as phenyl acetate and lactonase activities. Human serum paraoxonase activity has been shown to be inversely related to the risk of cardiovascular disease [40,41], as shown in atherosclerotic, hypercholester-olemic, and diabetic patients [42-44]. In 1998 HDL-associated PON 1 was shown to protect LDL, as well as the HDL particle itself, against oxidation induced by either copper ions or free radical generators [45,46], and this effect could be related to the hydrolysis of the specific lipoproteins oxidized lipids such as cholesteryl linoleate hydroperoxides and oxidized phospholipids. Protection of HDL from oxidation by PON 1 was shown to preserve... 

The first reported pesticide hydrolyses by an organometallic complex, which are the paraoxon and parathion hydrolysis by the aqueous molybdenocene dichloride (CP2M0CI2), have been reported. The synthesis and structural characterisation of a new one-to-one charge-transfer salt ferromagnet which is constructed from decamethylchromocene and dimethylcyanofumarate have been... 

Noncatalytic Reactions Chemical kinetic methods are not as common for the quantitative analysis of analytes in noncatalytic reactions. Because they lack the enhancement of reaction rate obtained when using a catalyst, noncatalytic methods generally are not used for the determination of analytes at low concentrations. Noncatalytic methods for analyzing inorganic analytes are usually based on a com-plexation reaction. One example was outlined in Example 13.4, in which the concentration of aluminum in serum was determined by the initial rate of formation of its complex with 2-hydroxy-1-naphthaldehyde p-methoxybenzoyl-hydrazone. ° The greatest number of noncatalytic methods, however, are for the quantitative analysis of organic analytes. For example, the insecticide methyl parathion has been determined by measuring its rate of hydrolysis in alkaline solutions. 

The rat LD qS are 13, 3.6 (oral) and 21, 6.8 (dermal) mg/kg. Parathion is resistant to aqueous hydrolysis, but is hydroly2ed by alkah to form the noninsecticidal diethjlphosphorothioic acid and -nitrophenol. The time required for 50% hydrolysis is 120 d ia a saturated aqueous solution, or 8 h ia a solution of lime water. At temperatures above 130°C, parathion slowly isomerizes to 0,%diethyl 0-(4-nitrophenyl) phosphorothioate [597-88-6] which is much less stable and less effective as an insecticide. Parathion is readily reduced, eg, by bacillus subtilis ia polluted water and ia the mammalian mmen to nontoxic 0,0-diethyl 0-(4-aminophenyl) phosphorothioate, and is oxidized with difficulty to the highly toxic paraoxon [511-45-5] diethyl 4-nitrophenyl phosphate d 1.268, soluble ia water to 2.4 mg/L), rat oral LD q 1.2 mg/kg. 

In soil and sediments, methyl parathion adsorbs to soil and is expected to display moderate mobility (EPA 1980c). The major degradation process of methyl parathion in soil is biodegradation by microbes (Badway and El-Dib 1984). Degradation by hydrolysis has been observed to occur at higher temperatures... 

Methyl parathion is rapidly degraded in natural water systems. The degradation of methyl parathion occurs much more rapidly in alkaline (pH 8.5) than in neutral (pH 7) or acidic (pH 5) conditions (Badawy and El-Dib 1984). A hydrolysis half-life of 72-89 days was calculated for fresh water at 25° C and pH<8 (EPA 1978c Mabey and Mill 1978) compared with about 4 days at 40° C and pH>8 (EPA 1978c). 

The degradation of methyl parathion by hydrolysis and biodegradation was studied in four types of water (ultrapure water, pH 6.1 river water, pH 7.3 filtered river water, pH 7.3 and seawater, pH 8.1) maintained at 6 and 22° C, in the dark. The half-lives of methyl parathion at 6° C in the four water types were determined to be 237, 95, 173, and 233 days, respectively, and the half-lives at 22° C were... 

Albanis TA, Pomonis PJ, Sdoukos AT. 1988c. The influence of fly ash on hydrolysis, degradation and adsorption of methyl parathion in aqueous soil suspensions. Toxicol Environ Chem 17 351-362. 

Sharmila M, Ramanand K, Sethunanthan N. 1981. Hydrolysis of methyl parathion in a flooded soil. 

The main purpose of this work is development of small-scale and mobile dsMmposition system of these chemicals. A number of studies on decomposition of organophosphorus insecticides have been conducted [1-3]. It is well known that or nophosphorus insecticides are decomposed by hydrolysis under alkaline condition, and its meciianisms have been studied [4], Even so, relatively few papers have address the devdopment of kinetic equations for reactor desipi. In this study, we aim to get kinetic equaticms for their decomposition under alkaline condition. As organophosphtous, we used parathion, fenitrothion, diazinon, malathion and phenthoate. 

Of the three organic phosphorus insecticides—hexaethyl tetraphosphate, tetraethyl pyrophosphate, and parathion—the first two have been shown to be mixtures (36) that contain tetraethyl pyrophosphate as the principal active ingredient. Several methods have been proposed for the determination of this compound in the commercial products (25, 35). All are based on the separation of the tetraethyl pyrophosphate from the related ethyl phosphates, followed by its hydrolysis to diethyl orthophosphoric acid and titration with standard alkali. Both hexaethyl tetraphosphate and tetraethyl pyrophosphate are soluble in water and are rapidly hydrolyzed to monoethyl and diethyl orthophosphoric acid. This rapid hydrolysis to nontoxic products greatly limits the duration of the in- secticidal effectiveness of tetraethyl pyrophosphate, but it also eliminates the danger of toxic residues on the crops treated. 

Pure parathion is a pale yellow, practically odorless oil, which crystallizes in long white needles melting at 6.0° C. (17). It is soluble in organic solvents, except kerosenes of low aromatic content, and is only slightly soluble in water (15 to 20 p.p.m. at 20° to 25° C.). Peck (35) measured its rate of hydrolysis to diethyl thiophosphate and nitro-phenate ions in alkaline solutions. He found that the reaction kinetics are first order with respect to the ester and to hydroxyl ion. In normal sulfuric acid the rate of hydrolysis was the same as in distilled water. Peck concluded that hydrolysis takes place by two mechanisms—a reaction catalyzed by hydroxyl ions and an independent uncatalyzed reaction with water. He calculated that at a pH below 10 the time for 50% hydrolysis at 25° C. is 120 days in the presence of saturated lime water the time is 8 hours. The over-all velocity constant at 25° C. is k = 0.047 [OH-] + 4 X 10-6 min.-1... 

The purified tetraethyl pyrophosphate is a colorless, odorless, water-soluble, hygroscopic liquid (24, 4 )- It possesses a very high acute toxicity (28), exceeding that of parathion, and is rapidly absorbed through the skin. There is no spray-residue problem, however, for tetraethyl pyrophosphate hydrolyzes even in the absence of alkali to nontoxic diethyl phosphoric acid. Hall and Jacobson (24) and Toy (47) have measured its rate of hydrolysis, which is a first-order reaction. Its half-life at 25° C. is 6.8 hours and at 38° C. is 3.3 hours. Coates (10) determined the over-all velocity constant at 25° C. k = 160 [OH-] + 1.6 X 10 3 min.-1 Toy (47) has described an elegant method for preparing this ester as well as other tetraalkyl pyrophosphates, based upon the controlled hydrolysis of 2 moles of dialkyl chlorophosphate ... 

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