Prenatal effects of 2,4,5-T, 2,4,5-trichlorophenol, and phenoxyacetic acid in mice

The herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and two structurally related compounds, phenoxyacetic acid and 2,4,5-trichlorophenol, were suspended in a 1:1 solution of honey:water and administered by gavage to pregnant mice on one of gestation days 8-15 (copulation plug day = day 1) or on three consecutive days (7-9, 10-12, or 13-15). Doses were 800-900 mg/kg for single and 250-300 mg/kg/day for multiple treatments. With the exception of 2,4,5-trichlorophenol treatment on day 14, only 2,4,5-T treatment significantly increased prenatal mortality, and only 2,4,5-T was associated with decreased fetal weight when comparisons were made with the solvent controls. Although low incidences were seen in all treatment groups, only 2,4,5-T significantly increased cleft palate or other gross malformations. Significant skeletal, visceral or histopathological defects were not observed. These results indicate that both the carboxyl group and chlorination of the aromatic ring are essential for an unambiguous teratogenic response.