Sister chromatid exchanges in chick embryos after treatment with the phenoxy herbicide MCPA.

The phenoxyherbicide and peroxisome proliferator 2-methyl-4-chlorophenoxyacetic acid (MCPA) was tested for its ability to induce sister-chromatid exchanges (SCE) in chick embryos. Erbitox E30 (a commercial formulation containing 28% MCPA sodium potassium salt as active ingredient) was injected into the air chamber in concentrations of MCPA of 0, 0.35, 0.7, 1.4, 2.8, or 5.6 mg/egg on day 0 of incubation. Pure MCPA sodium salt was tested at 2.8 mg/egg. Neutral red at 0.25 mg/egg was the mutagenic reference compound (positive control group). Eggs were then incubated for 4 days. MCPA induced a slight but significant increase in SCE frequency (about 1.3 times base line) at 2.8 mg/egg. The dose of 5.6 mg/egg was toxic. No difference in genetic activity between the commercial formulation and the pure compound was found. A cell cycle delaying effect of MCPA was evident at all the dose levels tested. The mitotic index remained unchanged.