EVALUATION OF CARBENDAZIM FOR GENE-MUTATIONS IN THE SALMONELLA AMES-PLATE-INCORPORATION ASSAY - THE ROLE OF AMINOPHENAZINE IMPURITIES

Benomyl (methyl tylamino)carbonyl]-1H-benzimidazol-2-yl]carbamate) and its major metabolite carbendazim (methyl 2-benzimidazolecarbamate) ar e major agricultural systemic fungicides. These compounds inhibit fung al microtubular function and thereby cause nondisjunction of chromosom es at cell division. Several investigators have proposed that these co mpounds can also cause gene mutations (base-pair substitutions). In th is laboratory, no mutagenic activity was observed with either benomyl (analytical grade) or Benlate(R) (samples tested up to 500 and 1200 mu g/plate, respectively, the limit of cytotoxicity) in the Salmonella/Am es plate-incorporation test in either base-pair substitution (TA100 an d TA1535) or frameshift-sensitive (TA98 and TA1537) strains with or wi thout S9 metabolic activation. However, some carbendazim preparations caused mutations in frameshift-sensitive strains at very high concentr ations (greater-than-or-equal-to 5000 mug/plate) with metabolic activa tion. The mutagenic activity was not due to the major carbendazim meta bolite, methyl (5-hydroxy-1H-benzimidazol-2-yl)carbamate (5-OH MBC), s ince 5-OH MBC was not mutagenic with (up to 20000 mug/plate) or withou t (up to 16000 mug/plate) activation. Subsequently, two highly mutagen ic contaminants. 2,3-diaminophenazine (DAP) and 2-amino-3-hydroxyphena zine (AHP) were detected in mutagenic carbendazim samples. In those sa mples, DAP and AHP contaminant levels ranged as high as 46.5 and 11.6 ppm, respectively. No evidence of mutagenicity could be detected in pr eparations in which the DAP content was < 1.8 ppm. The mutagenic activ ity of these two contaminants was further investigated in strain TA98. Without activation, DAP and ABP were positive at test concentrations as low as 5 and 10 mug/plate, respectively. In the presence of S9, mut ations were detected at much lower concentrations (beginning at 0.025 and 0.05 mug/plate, respectively). These results indicate that carbend azim samples containing DAP or AHP at levels as low as 5 or 10 ppm, re spectively, would be positive in the Salmonella/Ames test with activat ion when tested at 5000 mug/plate. Purified carbendazim is not mutagen ic.