Genotoxic effects of paraquat and diquat evaluated by sister-chromatid exchange, chromosomal aberration and cell-cycle rate

We studied the induction of sister-chromatid exchanges (SCEs) and chromosomal aberrations in cultured mammalian cells exposed to paraquat or diquat in order to elucidate the genotoxic effects of these two common herbicides. The effects of paraquat and diquat were studied at various concentrations with special attention given to concentrations that are thought to be non-toxic. With increasing concentrations of paraquat and diquat (0.08-20.0 mum), increasing frequencies of SCEs were found in Chinese hamster lung cells. The effects of the herbicides on the cell-cycle rate were also studied: the cycle rate was stimulated at low concentrations but inhibited at higher concentrations. There was no significant induction of chromosomal aberrations at herbicide concentrations that stimulated the cell-cycle rate. However, at concentrations found to inhibit the cell-cycle rate, an increased number of chromatid gaps and breaks were observed, especially after long incubation periods, although no chromatid exchanges were noted during our experiments. These results show that the genotoxic effects of paraquat and diquat occur not only at high concentrations, but also at concentrations low enough to stimulate the cell-cycle rate. The role of superoxide anions and/or hydrogen peroxide, produced by herbicide action, in the induction of sister-chromatid exchanges and chromosomal aberrations was demonstrated by further studies using catalase and/or superoxide dismutase treatment.