Carcinogenicity methyl parathion

Estimates of exposure levels posing minimal risk to humans (Minimal Risk Levels or MRLs) have been made for methyl parathion. An MRL is defined as an estimate of daily human exposure to a substance that is likely to be without an appreciable risk of adverse effects (noncarcinogenic) over a specified duration of exposure. MRLs are derived when reliable and sufficient data exist to identify the target organ(s) of effect or the most sensitive health effect(s) for a specific duration within a given route of exposure. MRLs are based on noncancerous health effects only and do not consider carcinogenic effects. MRLs can be derived for acute, intermediate, and chronic duration exposures for inhalation and oral routes. Appropriate methodology does not exist to develop MRLs for dermal exposure. 

No studies were located regarding carcinogenic effects in humans or animals after inhalation exposure to methyl parathion. 

EPA (1988a) has discussed the results of another carcinogenicity bioassay on methyl parathion in rats. Results of this study have not been presented in a peer-reviewed scientific journal and are not available to the public. 

NCI. 1979. Bioassay of methyl parathion for possible carcinogenicity. Bethesda, MD U.S. Department of Health, Education, and Welfare, National Institutes of Health, National Cancer Institute, Carcinogenesis Testing Program. DHEW (NIH) Publication No. 79-1713 NCI-CG-TR-157, 112. 

A 2-year bioassay of methyl parathion in mice and rats did not demonstrate any increased incidence of tumors in dosed animals. The lARC has concluded that there is no evidence that methyl parathion is carcinogenic to experimental animals. ... 

National Cancer Institute Bioassay of Methyl Parathion for Possible Carcinogenicity, TR-157. DHEW (NIH) Pub No 79-1713. Washington, DC, US Government Printing Office, 1979... 

U.S. National Cancer Institute. Bioassay of Methyl Parathion for Possible Carcinogenicity. NCI Carcinogenesis Technical Report Series No. 157. Washington, D.C. U.S. Government Printing Office,... 

Chronic toxicity of organophosphates may be discussed under four different areas carcinogenicity, delayed neurotoxicity, experimental myopathy, and, in humans, psychiatric disorders. In 1983, the IARC (International Agency for Research on Cancer) evaluated the carcinogenic potential of, among other pesticides, five organophosphate insecticides/acaricides (malathion, methyl parathion, parathion,... 

There are no known 5-containing compounds in tobacco or tobacco smoke in Group 1, 2A, or 2B. There are only six compounds that are found in Group 3 (Malathion , ethylenethiourea, Parathion , Parathion-methyl , sulfur dioxide, and ethylene sulfide). The evidence for the carcinogenicity in humans of aU these compounds was classified as inadequate (18A04). 

Carcinogenic hydrocarbons have been reported to increase the activity of this oxidising enzyme system in immature males, adult females and partially hepatectomized adult males [47]. This involves the synthesis of new enzyme protein which may be prevented by ethionine, a competitive antagonist to the incorporation of methionine into new protein [48]. The microsomal enzyme inhibitor SKF 525A similarly prevents oxidation of the phosphoro-thionates, so reducing their toxicity [47], Similar observations on the influence of sex hormones, age and microsomal enzyme inducers on the toxicity of schradan [49, 50], parathion [51, 52], fenitrothion [53], EPN. 0-(4-methyl-7-hydroxycoumarin)-0,( -diethylphosphorothionate (E838) [51] and 0,0-diethyl-0-(3-methyl-4-methylthiophenyl)phosphorothionate (DMP) [54] in rats have been reported. 

---