Genotoxicity of a mixture of three widely used herbicides in chick embryo B cells

The cytogenetic effects of a mixture of three herbicides in common use, namely molinate, 2,4-D and MCPA were evaluated in chick embryo B cells in vivo. This nonmammalian test system has been validated for both direct- and indirect-acting mutagens and may have a predictive value for environmental mutagens. Actual exposures of humans and animal species in the wild are due to complex mixtures that include not only the active ingredients but also other chemicals (e.g. solvents, emulsifiers) and, eventually, impurities. The thiocarbamate herbicide molinate is used in the first stages of rice cultivation to control the germinating of water grasses and broadleaf plants and the phenoxy herbicides 2,4-D and MCPA are used as post-emergence herbicides. Of interest, associations with non’Hodgkin lymphoma and exposure to phenoxy herbicides have been reported in some epidemiological studies, while the results of experimental carcinogenicity studies are yet inconclusive. Molinate will be phased out of US pesticide market by 2009 (EPA, 2004). 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). On day 19, cells were harvested for sister chromatid exchange (SCE) analysis. The herbicides induced a marginally significant (P < 0.05) increase in SCE frequency and caused cell cycle delay and reduction of the mitotic index. As yet, there are only results from genotoxicity studies of individual herbicides. At the same experimental conditions, 2,4-D was negative and MCPA was marginally positive in chick embryo allantoic red blood cells after 10 D.I. Recently, molinate gave positive responses using the Drosophila wing spot test (Kaya et al., 2004).