Sister chromatid exchange and cell cycle progression in avian B lymphocytes following exposure to herbicide MCPA

2,4-D (2,4-dichlorophenoxyacetic acid) and MCPA (2-methyl-4-chlorophenoxyacetic acid) are widely used post-emergence herbicides. Phenoxyherbicides induce peroxisome proliferation, as do other structurally related or unrelated chemicals which have been demonstrated to be nongenotoxic carcinogens in rodents. Agricultural herbicide use has been associated with increased risk of non-Hodgkin’s lymphoma., while the results of experimental carcinogenicity studies are yet inconclusive. Both 2,4-D and MCPA gave mixed results in genotoxicity studies. Of interest, 2,4-D caused a slight proliferative effect in human lymphocytes exposed in vitro and in chick embryos treated before incubation. Inhibition of intercellular communication has been reported in cultures of Chinese hamster V79 cells . Together these results favor the hypothesis that phenoxy herbicides might be tumor promoters. The objective of the present study was to evaluate the effects of MCPA on sister chromatid exchange frequency and cell cycle kinetics in avian B lymphocytes. This in vivo test system has good potentialities for evaluating the genotoxicity of xenobiotics of environmental relevance. Chick embryos were treated via the air cell route on day 10 of incubation, a formative and potentially sensitive period in B-cell development (stem cells seeding and differentiation). A commercial formulation containing 25% of MCPA sodium salt as active ingredient and pure MCPA were tested. The bursa of Fabricius was removed on day 19 of incubation. The present findings suggest that MCPA is a weak mutagen. Changes in cell cycle progression were observed.