Carcinogenicity and toxicity of malathion and malaoxon.

Malathion and its oxygen analogue, malaoxon, are carcinogenic in Osborne-Mendel and Fischer-344 rats. Benign and malignant neoplasms at all sites were increased in Osborne-Mendel and Fischer-344 male and female rats ingesting malathion. Both Osborne-Mendel and Fischer-344 male rats were more susceptible than the female rats. The organ sites were not the same for Fischer-344 and Osborne-Mendel rats. Osborne-Mendel rats developed neoplasms of the endocrine organs, brain, and liver. Fischer-344 rats had neoplasms of the adrenal medulla, organs with squamous cells, lung, and hematopoietic system. Fischer-344 male rats given malathion were more susceptible to chronic renal disease, parathyroid hyperplasia, metastatic calcification, and atrophy of the testes than were Osborne-Mendel male rats. They also had ulcers of the forestomach. Chronic renal disease and atrophy of the testes affected the health of the animals and interfered with the development of neoplasms. Malathion increased the incidence of neoplasms of the liver in B6C3F1 male mice. Male mice also had atrophy of the testes. Benign and malignant neoplasms at all sites, and in the endocrine organs, were increased in Fischer-344 male and female rats ingesting malaoxon. Neoplasms were present in the adrenal medulla, organs with squamous cells, liver, and hematopoietic system. Both male and female Fischer-344 rats receiving malaoxon had chronic renal disease and the male rats had parathyroid hyperplasia and metastatic calcification.