the injection site. In a rat body MC has a half-life of about 4 weeks. After 8 weeks, 80% of MC is metabolized into water-soluble metabolites. MC and its metabolites mainly exit the body via feces (a ninefold more urine). Three months after injection with MC, 85% of the rats are reported to have tumors. 82% of the tumors is a form of spindle-cell sarcoma. Efficacy Methylcholanthrene is often used to induce tumors in rodents for carcinogenesis and mutagenesis research. In a study from 1991, lung precancerous and cancerous lesions were induced in Wistar rats by one intrabronchial injection of 3-MC. After 30 days, atypical hyperplasia of bronchiolar epithelium, adenoid hyperplasia or adenomas, and squamous cell carcinoma occurred in 15 (88.2%), 12 (70.6%) and 3 (17.7%) out of 17 rats respectively. After 60 days, the incidences were 15/18 (83.3%), 4/17 (23.5%) and 7/18 (38.9%). All of the precancerous lesions and carcinomas showed positive expression of gamma-glutamyltranspeptidase (GGT). Jin et al. (2013) found that the cellular redox balance is altered by acute exposure to 3-MC. This causes the nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated response pathway to induce antioxidant responses. Toxicity 3-MC is a ligand of the aryl hydrocarbon receptor (AhR), which stimulates transcription directed by xenobiotic response elements. AhR ligands can induce formation of an AhR-estrogen receptor (ER) complex. 3-MC was found to elicit estrogenic activity by this mechanism, and by stimulation of the expression of some endogenous ER target genes. 3-MC may cause respiratory tract irritation, skin irritation or eye irritation. Effects on animals Effects on human 3-MC is mutagenic to human cells. Curren et al. (1978) were the first to report successfully induced mutations in human cells with 3-MC. Skin epithelial cells are thought to metabolize the compound to mutagenic products. The ability to metabolize mutagens may express genetically regulated differences within a species such as man or mouse, causing environmental chemicals to show a different level of mutagenicity and carcinogenicity to specific individuals. Non-human toxicity studies The administration of 3-MC to pregnant mice results in the formation of lung tumors in the offspring. Miller et al. (1990) compared the effects of fetal versus adult exposure to 3-MC on both induction of aryl hydrocarbon hydroxylase (AHH) activity in lung and dependence of lung tumorigenesis on the Ah genotype. A single ip injection (in inducible fetal lung supernatants) of 100 mg/kg of 3-MC to the mothers resulted in