0,0-Diethyl 0- phosphorothioate toxicity

Fawade MM, Pawar SS. 1978. Alterations in mixed function oxidase system during thiodemeton (o-o diethyl S-2(ethylthio) ethyl phosphorothioate) toxicity. Indian J Exp Biol 16 481-484. 

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. 

It is important to emphasize that the initial metabolites after hydrolysis may be both toxic and sometimes resistant to further degradation. Examples include nitrophenols, whose degradation is discussed in Chapter 9, Part 5 and 3,5,6-trichloropyridin-2-ol (Feng et al. 1997), which is produced by the hydrolysis of chlorpyrifos (0,0-diethyl-0-[3,5,6-trichlo-2-pyridyl]phosphorothioate). 

Shaffer, C.B. and West, B. (1960). The acute and subacute toxicity of technical o,o-diethyl s-2-diethyl-aminoethyl phosphorothioate hydrogen oxalate (TETRAM). Toxicol. Appl. Pharmacol. 2 1-13. 

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). 

IUPAC name O, O-diethyl O-4-nitrophenyl phosphorothioate Molecular formula C10H14NO5PS Toxicity class USEPA I WHO la... 

By way of offering a wider perspective on the range of compounds that have been evaluated and the different fish that have been used in early life-stage evaluations, it may be mentioned that the Californian grunion (Leures-thes tenuis) has been employed for assessing the toxicity of chlorpyrifos (0,0-diethyl-0-(3,5,6-trichloro-2-pyridyl) phosphorothioate (Goodman et al. 1985) and pike (Esox Indus) for 2,3,7,8-tetrachlorodibenzo[l,4]dioxin (Helder 1980). 

The thio analogue of paraoxon, diethyl-p-nitrophenyl phosphorothioate (parathion, 17), is practically more adequate because of its lower toxicity to warmblooded animals and higher stability against hydrolysis. It was prepared by Schrader in 1944, and the elucidation of its biological properties was due to Kiikenthal and Unterstenhofer (Schrader and Kukenthal, 1948 Unterstenhofer, 1948 Schrader, 1952b). 

Diethyl-0-[4-(methylsulfonyl)phenyl] phosphorothioate (fensulfothion, 11), used also as insecticide, exhibits a potent nematocidal action against almost all the phytopathogenic nematodes (Schegk and Schrader, 1958). Its solubility in water is somewhat better than that of dichlofenthion. It is very toxic, its oral ld,o for female rats being 2.2 mg/kg, and for male rats 10.5 mg/kg. 

On investigating the relationship between the action and structure of the compounds, Kado (1969) established that S-benzyl-0,0-dialkyl derivatives are more effective than the respective O-benzyl-phosphate, phosphorothioate and phosphorodithioate derivatives. The 0,0-diisopropyl derivative is more stable than the diethyl derivative and at the same time less toxic to warm-blooded organism (Yamamoto et al., 1973). Recently, 15000 tons of the diisopropyl derivative (IBP), marketed under the name Kitazin P , has been used in Japan for prevention of rice blast (Searle et al., 1973). 

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