Cytogenetic effects of short- and long-term exposure of chick embryos to the phenoxyherbicide 2,4-D.

Before incubation, chick embryos were treated with the herbicide 2,4-dichlorophenoxy acetic acid (2,4-D) by injecting onto the inner shell membrane solutions of 0, 0.5, 1, 2, or 4 mg 2,4-D. A commercial formulation containing 37% 2,4-D iso-octyl ester as active ingredient and pure 2,4-D were tested. Sister chromatid exchange (SCE) and cell cycle kinetics were examined at days 4, 7, and 10 from 22 to 30 embryos per group. After 4 days of exposure to commercial 2,4-D, a small (P < 0.05) dose-related increase of SCE was seen for the 4-mg group. An enhanced SCE response upon long-term exposure to 2,4-D was apparent. After 10 days of exposure, SCE frequencies for the 2- and 4-mg commercial 2,4-D, and 4-mg pure 2,4-D groups were significantly higher than for the controls. A significant slowing of cell cycle at concentrations at and above 1 mg was seen. Also observed was a slight, not statistically significant proliferative effect at the lowest dose of 0.5 mg/embryo. Consistent with the results from other test systems, the present findings indicate that 2,4-D has a low to moderate genotoxic activity.