Am. Sarrif et al., EVALUATION OF CARBENDAZIM FOR GENE-MUTATIONS IN THE SALMONELLA AMES-PLATE-INCORPORATION ASSAY - THE ROLE OF AMINOPHENAZINE IMPURITIES, MUTATION RESEARCH, 321(1-2), 1994, pp. 43-56
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.