Parathion, decomposition

Surface catalysis affects the kinetics of the process as well. Saltzman et al. (1974) note that in the case of Ca -kaolinite, parathion decomposition proceeds in two stages with different first-order rates (Fig. 16.14). In the first stage, parathion molecules specifically adsorbed on the saturating cation are quickly hydrolyzed by contact with the dissociated hydration water molecules. In the second stage, parathion molecules that might have been initially bound to the clay surface by different mechanisms are very slowly hydrolyzed, as they reach active sites with a proper orientation. 

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. 

Almost same relationships were also found for other two organophosphorus insecticides, parathion and diazinon. So second-order decomposition rate constants were used to evaluate all of the organophosphorus insecticides, where the second-order decomposition rate constants were calculated by dividing the first-order doiomposition rate constants by the sodium hydroxide concentration. Rate constants of malathion and phenthoate could not be obtained, because these rmetion rates were too fast to analyze. 

Choice of Solvent. As indicated by Averell and Norris (1), and independently confirmed by the authors, technical benzene is a superior stripping solvent for parathion residues. It is almost completely miscible with technical grade parathion at room temperatures, it is universally available and low in cost, it is readily volatile, it fails to contribute to storage decomposition (6), it is a good solvent for plant oils and waxes, and it is immiscible with water. On the other hand, benzene is highly flammable and its vapors are very toxic to human beings, especially as a chronic toxicant even in small doses. 

Diethyl p-nitrophenyl phosphate, the oxygen analog of parathion, was investigated to ascertain whether it would interfere, if present, in the determination of parathion. It was found, however, under the conditions used in this method to have a decomposition potential of —0.37 volt and a half-wave potential of —0.47 volt. 

McPherson, J. B. et al., J. Agric. Food Chem., 1956, 4, 42-49 Overheating during removal of solvent by distillation from a pilot batch of methyl parathion led to explosive decomposition, and the course of the 2-stage decomposition was studied. A 1.5 g sample immersed at 270°C decomposes after an induction period of 54 s and the residue later deflagrates, but a 5 g sample deflagrates during the initial decomposition. 

Vacuum distillation of parathion at above 100°C is hazardous, frequently leading to violent decomposition [1], Following a plant explosion, the process design was modified and featured a high degree of temperature sensing and control to avoid a recurrence [2],... 

At 130 °C, parathion isomerizes to O.S-diethyl 0-4-nitrophenyl phosphorothioate (Hartley and Kidd, 1987 Worthing and Hance, 1991). An 85% yield of this compound was reported when parathion was heated at 150 °C for 24 h (Wolfe et al, 1976). Emits toxic oxides of nitrogen, sulfur, and phosphorus when heated to decomposition (Lewis, 1990). 

ChemicaPPhysical. Emits toxic fumes of phosphorus, nitrogen, and sulfur oxides when heated to decomposition (Sax and Lewis, 1987). Methidathion oxon was also found in fogwater collected near Earlier, CA (Glotfelty et ah, 1990). It was suggested that methidathion was oxidized in the atmosphere during daylight hours prior to its partitioning from the vapor phase into the fog. On 12 January 1986, the distributions of parathion (0.45 ng/my in the vapor phase, dissolved phase, air particles, and water particles were 57.5, 25.4, 16.8, and 0.3%, respectively. For methidathion oxon (0.84 ng/m3), the distribution in the vapor phase, dissolved phase, air particles, and water particles were <7.1, 20.8, 78.6, and 0.1%, respectively. 

Kotronarou, A., Mills, G., and Hoffmann, M.R. Decomposition of parathion in aqueous solution by ultrasonic irradiation,... 

Figure 12.8 shows an example of parathion distribution in sterilized and natural, biologically active Gilat soil columns. We see that, at relatively early times, when the effect of decomposition is minimal, the parathion distribution is similar to that in the sterile soil. After four days, the effect of microbial activity on decomposition is evident, and the distribution pattern is significantly different. After seven days, the parathion is almost completely decomposed. This example emphasizes the necessity to consider additional processes, snch as degradation, in analyses of pollutant transport. 

An equation that accounts for parathion transport, snbject to both diffnsion and microbial decomposition, can be written as... 

The first of the organophosphorus insecticides to gain widespread use was parathion which is still an important commercial pesticide. This compound (Figure 9) is converted to the S-ethyl isomer by heating whereas paraoxon, a more toxic compound, is formed by enzymic action in plants. In animals, the additional products, p-nitrophenol and p-amino-phenol, are also formed. At present, little information appears to be available regarding the decomposition products of parathion in soils. 

SAFETY PROFILE Poison by inhalation, ingestion, skin contact, intravenous, and intraperitoneal routes. An experimental teratogen. Other experimental reproductive effects. Human mutation data reported. Questionable carcinogen with experimental tumorigenic data. See also PARATHION and ESTERS. When heated to decomposition it emits very toxic fumes of POx, SOx, and NOx. 

SAFETY PROFILE Deadly poison by skin contact. Poison by ingestion. A cholinesterase inhibitor. See also PARATHION. Trace HCl catalyzes a hazardous reaction during the preparation of diethyl phosphate from diethyl chlorophosphate. When heated to decomposition it emits very toxic fumes of Cr and POx. 

SAFETY PROFILE Poison by ingestion. When heated to decomposition it emits very toxic fumes of POx and SOx. See also PARATHION. 

ACGIH TLV TWA 0.05 mg/m (skin) Not Classifiable as a Human Carcinogen SAFETY PROFILE Poison by ingestion, skin contact, and intraperitoneal routes. Human systemic effects by ingestion flaccid paralysis without anesthesia, motor activity changes, fever, and inhibition of cholinesterase. When heated to decomposition it emits highly toxic fumes of SOx and POx. See also PARATHION. 

SAFETY PROFILE Human poison by inhalation, skin contact, and intravenous routes. Experimental poison by ingestion, inhalation, skin contact, subcutaneous, intravenous, intraperitoneal, and intramuscular routes. A nerve gas. Vapor does not penetrate skin liquid does so rapidly. The primary physiological action is on the sympathetic nervous system, causing a vasoparesis (partial paralysis of the vasomotor nerves, which control the diameter of the blood vessels). Vapors when inhaled can cause nausea, vomiting, and diarrhea, which can be followed by muscular twitching and convulsions. Flammable when exposed to heat or flame can react with oxidizing materials. When heated to decomposition it emits very toxic fumes of POx, CN, and NOx. See also PARATHION and CYANIDE. 

SAFETY PROFILE A deadly human poison by skin contact and inhalation. (A small drop on the skin can kill a man.) A deadly experimental poison by ingestion, inhalation, skin contact, subcutaneous, intravenous, intramuscular, and intraperitoneal routes. Human systemic effects muscle weakness, bronchiolar constriction, nausea or vomiting, flaccid paralysis without anesthesia, miosis (pupOlar constriction), cholinesterase inhibition. A nerve gas used as a chemical warfare agent. To fight fire, use foam, CO2, drj chemical. When heated to decomposition or reacted with steam, it emits very toxic fumes of F and PO.. See also PARATHION. 

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