Genotoxic potential of glyphosate formulations: mode-of-action investigations.

A broad array of in vitro and in vivo assays has consistently demonstrated that glyphosate and glyphosate-containing herbicide formulations (GCHF) are not genotoxic. Occasionally, however, related and contradictory data are reported, including findings of mouse liver and kidney DNA adducts and damage following intraperitoneal (ip) injection. Mode-of-action investigations were therefore undertaken to determine the significance of these contradictory data while concurrently comparing results from ip and oral exposures. Exposure by ip injection indeed produced marked hepatic and renal toxicity, but oral administration did not. The results suggest that ip injection of GCHF may induce secondary effects mediated by local toxicity rather than genotoxicity. Furthermore, these results continue to support the conclusion that glyphosate and GCHF are not genotoxic under exposure conditions that are relevant to animals and humans.

Mammalian toxicology overview and human risk assessment for sulfosulfuron.

Sulfosulfuron is a low-use rate sulfonylurea herbicide. A review of the toxicity database for sulfosulfuron indicates that the molecule has a low order of acute toxicity. It is not genotoxic and is not a reproductive, developmental, or nervous system toxicant. There were no indications of endocrine disruption in any study performed with the molecule. The only findings considered to be an adverse effect in mammalian laboratory animals following prolonged subchronic or chronic exposure to sulfosulfuron were isolated to the urinary tract. These findings occurred in conjunction with findings of urolith formation following high-level chemical dosing, resulting in epithelial hyperplasia that, in a few cases, progressed to tumor formation. Mode-of-action information supports the conclusion that these tumors result from a non-genotoxic, threshold-based process that is well established and widely considered to be not relevant to humans. Based on its short-term, infrequent application pattern and very low use rate and crop residues, aggregate and cumulative risk assessments indicate that sulfosulfuron has substantial margins of exposure and does not represent a significant risk to human health.

A review of the genotoxicity of triallate.

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.