Decreased red blood cell cholinesterase activity has also been reported in animal inhalation studies. In one study, degenerative changes in the liver were observed in dogs chronically orally exposed to parathion. High postnatal mortality was also observed in an animal study. No information is available on the carcinogenic effects of parathion in humans. EPA has classified parathion as a Group C possible human carcinogen.
Pure parathion is a pale yellow liquid, while the technical grades are brown.
References U.S. Department of Health and Human Services. National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993. World Health Organization, Lyon. 1983. The Merck Index. An Encyclopedia of Chemicals, Drugs, and Biologicals .