The presence of genotoxic and bioactive components in indigo dyed fabrics--a possible health risk?

Extracts of pure cotton and jeans fabrics were tested for mutagenicity in Salmonella typhimurium strains TA98 and TA100. The vat dye indigo, technical grade as well as 98% and greater than 99.5% pure, was also tested for mutagenicity. Synthetic indigo, indirubin and isatin were tested for TCDD receptor affinity in competition experiments in vitro. The mutagenicity of the extracts was associated with the cotton denim and nondyed cotton gave only marginal effects. The mutagenicity of the indigo dyed fabrics was dependent on type and treatment of the fabrics. Extracts of both bleached and nonbleached jeans gave mutagenic effects on TA98 +/- S9 and TA100 +/- S9. The greatest effects were seen in the presence of S9. Bleaching gave an additional increase in the mutagenicity in the absence of S9. Normal washing of the fabrics after bleaching reduced the mutagenicity. Synthetic indigo of technical grade or 98% pure showed mutagenic effects, especially on TA98 + S9. Further purification to 99.5% reduced the mutagenicity to 24 revertants/mg (6.2 rev/mu mole). Considering the amount of indigo in the extracts and its low mutagenicity, the genotoxicity of jeans extracts must be caused by other unknown components. However, indigo showed a high (Kd = 1.9 nM) affinity for the Ah or TCDD receptor. Indigo can therefore still be a potential health risk either by eliciting toxic effects of other compounds or by being a nongenotoxic carcinogen. The worldwide use of jeans with a possible exposure of a large population to genotoxic and biologically active components emphasizes the need for a more thorough characterization of these effects.