Chronic dietary toxicity and oncogenicity evaluation of MCPA (4-chloro-2-methylphenoxyacetic acid) in rodents.

The chronic toxicity and oncogenicity of 4-chloro-2-methylphenoxyacetic acid (MCPA) were evaluated in Wistar rats at target doses of 20, 80, and 320 ppm for 2 years. Chronic effects were noted in male and/or female rats in the 80- and 320-ppm dose groups, namely elevations in triglycerides and serum glutamic transaminase levels. Nephrotoxicity was confined to male rats in the 320-ppm dose group. The systemic NOEL was determined to be 20 ppm for male and female rats. No oncogenic potential was observed. Doses in the 2-year oncogenicity study in mice were 20, 100, and 500 ppm. Kidney weight changes with corresponding minor histopathological findings in the kidney were evident in females in the 500-ppm dose group. MCPA was determined to have no oncogenic potential in B6C3F1 mice. In summary, there is no evidence of any oncogenic potential after dietary exposure of MCPA in rats or mice even at doses where limited chronic toxicity is seen.