To be or not to be a carcinogen; delving into the glyphosate classification controversy

The International Agency for Research on Cancer (IARC) placed the most widely used herbicide glyphosate (GLY) into the category 2A (probably carcinogenic to humans), a classification questioned by experts from academia and industry. This article critically appraised the epidemiological and experimental data that led the IARC working group (WG) to consider GLY a probable human carcinogen and the ensuing controversy. An association of GLY with non-Hodgkin lymphoma was suggested by some observational studies. A non-causal explanation for this weak association, however, cannot be excluded. Contrary to WG's view, long-term rodent assays yielded no convincing evidence that GLY is carcinogenic. The mechanistic evidence remains elusive as well. Bacterial reverse mutation tests (including tester strains sensitive to oxidative mutagens) were clearly negative, and so were rodent genotoxicity assays by oral route. Tests with mammalian cells in vitro yielded conflicting results at high (cytotoxic) concentrations of GLY-based formulations. Conflicting results were also obtained when high doses of GLY-based herbicides were administered to rodents by the intraperitoneal route. Such high doses are unlikely to be attained in realistic scenarios of exposure. Finally, the IARC classification is based on a conjectural hazard, and rational public health interventions must be based on estimated risks.

Genotoxicity and oxidative stress as biomarkers in fresh water mussel, Lamellidens marginalis (Lam.) exposed to monocrotophos.

Monocrotophos (MCP) is an organophosphate pesticide widely used in India for controlling various pests. In this study, we evaluated the oxidative stress and genotoxic potential of MCP on the freshwater mussel Lamellidens marginalis (Lamarck) after 7 days exposure and repair of the damaged DNA after 4 days recovery. The bivalves were exposed to 5.25 mg/L of MCP for 7 days and then allowed to recover for 4 days in pesticide-free water. Increase in the levels of thiobarbituric acid reactive substances was recorded in the gill, muscle, foot and mantle tissues. Cellular antioxidant defences i.e. antioxidant enzyme activities like catalase, superoxide dismutase, glutathione reductase and glutathione-S-transferase were used as biomarkers of oxidative stress. Altered activities of antioxidant enzymes were observed after exposure. There was a significant recovery in the antioxidative enzymes in the tissues after the recovery period. To monitor genotoxicity of MCP, we used micronucleus and comet assay. Increase in Olive tail moment in the gill cells of exposed mussels as compared to that of control ones indicated significant DNA damage. Our findings suggest that the MCP-induced oxidative stress may be contributing partly to genotoxic damage of gill cells. Thus, these biomarkers are found to be useful in evaluating the toxicity of MCP in mussels.