Environmentally relevant exposures of male mice to carbendazim and thiram cause persistent genotoxicity in male mice

Carbendazim and thiram are fungicides used in combination to prevent mold destruction of crops. Studies have demonstrated genotoxicity by these agents, but have not used concentrations below their water solubility limits in drinking water to test for persistence of genotoxicity due to chronic exposure. Ten 8-week old male Swiss-Webster mice were exposed to tap water, or nominal concentrations of 20 μM carbendazim, 20 μM thiram or 20 μM of both fungicides for 90 days (total of 40 mice). Five mice from tap water controls, carbendazim, thiram and combination-treated groups (20 mice total) had genotoxicity detected by comet assay of lymphocytes at the termination of the exposure period. The other 20 mice (4 treatment groups) were all switched to tap water and allowed a 45-day recovery period to check for persistence of DNA damage. The damage was compared with commercial control cells exposed to increasingly harsh treatment by etopside. Comet assay (mean % tail DNA + SE) of control mice (9.8 + 0.9) was similar to commercial control (CC0) cells (8.5 + 0.9). Carbendazim, thiram or the combination treatment caused similar mean % tail DNA with 33.0 + 2.9, 30.1 + 3.3 and 29.1 + 1.8, respectively, comparable with commercial cells slightly damaged by etopside (CC1 with 31.4 + 2.9) with no statistical change in water or food intake, body weight or liver or kidney weights. The key result was that a 45-day recovery period had no observable difference in the DNA damage as assessed by DNA % in comet tail with tap water controls and CCO control cells at 7.0 + 0.7 and 9.7 + 1.2 versus 27.5 + 1.9, 29.3 + 2.2 and 32.0 + 1.8, respectively, for carbendazim, thiram and combination treatments. It is of concern that the use of these agents in developing countries with little training or regulation results in water pollution that may cause significant persistent DNA damage in animal or human populations that may not be subject to repair.