Cytogenetic effects of alachlor and/or atrazine in vivo and in vitro

The purpose of this study was to assess the cytogenetic effects of two commonly used herbicides, alachlor and atrazine, which are often found together in groundwater. Chromosome damage was examined in bone marrow cells of mice drinking water containing 20 ppm alachlor and/or 20 ppm atrazine, with an immunosuppressive dose of cyclophosphamide used as a positive control. Chromosome damage was also quantified in human lymphocytes exposed in culture to 1.0, 0.1, or 0.01 microgram/ml alachlor and/or atrazine. The in vitro study demonstrated dose related cytogenetic damage not associated with mitotic inhibition or cell death, with damage due to the alachlor-atrazine combination suggesting an additive model. The in vivo study also suggested additive damage due to the alachloratrazine combination after 30 days of treatment, but, unexpectedly, demonstrated less cytogenetic damage and fewer cells with multiple aberrations after 90 days. Also, at 90 days, all treated mice had elevated mitotic indices compared to controls. The fact that the elevated mitotic index was associated with immune suppression in the cyclophosphamide group suggests that death of cells with accumulated chromosomal aberrations resulted in increased bone marrow proliferation, so a higher fraction of cells examined were newer with less damage. Since the alachlor-atrazine combination treated mice showed little systemic toxicity despite bone marrow mitotic indices similar to the cyclophosphamide treated animals, as well as a similar decrease in cytogenetic damage at 90 days compared to 30 days, cell death and replacement must also be involved but cannot completely explain the results.