Triallate is a selective herbicidal chemical used for control of wild oats in wheat. It has an extensive genotoxicity database that includes a variety of in vitro and in vivo studies. The chemical has produced mixed results in in vitro assay systems. It was genotoxic in bacterial mutation Ames assays, predominantly in Salmonella typhimurium strains TA100 and TA1535 in the presence of S9. Weaker responses have been observed in TA100 and TA1535 in the absence of S9. Mixed results have been observed in strain TA98, whereas no genotoxicity has been observed in strains TA1537 and TA1538. The presence and absence of S9 and its source seem to play a role in the bacterial response to the chemical. There have also been conflicting results in other test systems using other bacterial genera, yeast, and mammalian cells. Chromosome effects assays (sister-chromatid exchange and cytogenetics assays) have produced mixed results with S9 but no genotoxicity without S9. Triallate has not produced any genotoxicity in in vitro DNA damage or unscheduled DNA synthesis assays using EUE cells, human lymphocytes, and rat and mouse hepatocytes. In a series of in vivo genotoxicity assays (cytogenetics, micronucleus, dominant lethal, and unscheduled DNA synthesis), there has been no indication of any adverse genotoxic effect. Metabolism data indicate that the probable explanation for the differences observed between the in vitro studies with S9 and without S9 and between the in vitro and the in vivo studies is the production of a mutagenic intermediate in vitro at high doses of triallate is expected to be at most only transiently present in in vivo studies. The weight of evidence strongly suggests that triallate is not likely to exert mutagenic activity in vivo due to toxicokinetics and metabolic processes leading to detoxification.
A proposal for a two-dose/single-sample in vivo/in vitro rat hepatocyte unscheduled DNA synthesis assay