Chronic dietary toxicity/oncogenicity studies on 2,4-dichlorophenoxybutyric acid in rodents.

2,4-Dichlorophenoxybutyric acid (2,4-DB) is principally used in the United States on peanuts, soybeans, and alfalfa. In Europe, it is used on cereals, undersown cereals, lucerne (alfalfa), clover, and clover mixtures. Doses in the 2-year chronic/oncogenicity rat study were 0, 60, 600, and 1800 ppm. No evidence of an oncogenic potential for 2,4-DB was evident and the study clearly established a NOEL of 2.48 mg/kg/day (60 ppm, males) and 3.23 mg/kg/day (60 ppm, females), as well as an MTD of 78.0 (1800 ppm, males) and 110.6 mg/kg/day (1800 ppm, females), for chronic effects of 2,4-DB in the rat. Doses in the 18-month mouse oncogenicity study were 0, 25, 250, and 750 ppm. No oncogenic effect was noted in the study. In summary, the findings of these studies indicate low chronic toxicity of 2,4-DB and the lack of oncogenic response to 2,4-DB following chronic dietary exposure of 2,4-DB in the rat and mouse.