CHRONIC DIETARY TOXICITY ONCOGENICITY STUDIES ON 2,4-DICHLOROPHENOXYACETIC ACID IN RODENTS/

Forms of 2,4-dichlorophenoxyacetic acid (collectively known as 2,4-D) are herbicides used eo control a wide variety of broadleaf and woody p lants. Doses in the 2-year chronic/oncogenicity rat study were 0, 5, 7 5, and 150 mg/kg/day. The chronic toxicity paralleled subchronic findi ngs, and a NOEL of 5 mg/kg/day was established. A slight increase in a strocytomas observed (in males only) at 45 mg/kg/day in a previously c onducted chronic rat study was not confirmed in the present study at t he high dose of 150 mg/kg/day. Doses In the 2-year mouse oncogenicity studies were 0, 5, 150, and 300 mg/kg/day for females and 0, 5, 62.5, and 125 mg/ kg/day for males. No oncogenic effect was noted in the stu dy. In summary, the findings of these studies indicate low chronic tox icity of 2,4-D and the lack of oncogenic response to 2,4-D following c hronic dietary exposure of 2,4-D in the rat and mouse. (C) 1996 Societ y of Toxicology