Mutagenicity of selected sulfonated azo dyes in the Salmonella/microsome assay: use of aerobic and anaerobic activation procedures.

A selection of 16 sulfonated azo dyes of both the monoazo type and diazo dyes based on benzidine, o-tolidine and o-dianisidine were assayed for mutagenicity in Salmonella typhimurium strains TA98 and TA100 employing both aerobic and anaerobic preincubation procedures. 3 food dyes, FD & C Red No. 40 and Yellows No. 5 and No. 6 were non-mutagenic in all tests. 5 dyes were mutagenic with aerobic treatment (trypan blue, Pontacyl Sky Blue 4BX, Congo Red, Eriochrome Blue Black B, dimethylaminoazobenzene) and 6 were mutagenic aerobically with riboflavin and cofactors (Deltapurpurin, trypan blue, Pontacyl Sky Blue 4BX, Congo Red, methyl orange, Ponceau 3R). Anaerobic preincubation involving enzymatic reduction of the dyes led to a different pattern of mutagenicity, with trypan blue giving much enhanced mutagenicity; Eriochrome Blue Black B, Pontacyl Sky Blue 4BX, Deltapurpurin and Congo Red exhibiting similar activity to aerobic preincubation; and methyl orange and Ponceau 3R yielding no mutagenicity. The results are interpreted with respect to an hypothesis involving partial reduction of the azo bond under differing degrees of aerobiosis via azo-anion radicals and hydrazo intermediates.