Evaluation of the mutagenicity and toxicity of monoazo dyes in wastewater effluents and sludge supernatants

Azo compounds represent a broad class of commercial dyestuffs that have been found in industrial effluents and other waters worldwide. They comprise approximately 60% of all commercially produced dyes used in industry. Large portions of these azo dyes manage to migrate into the environment. Due to the recalcitrant nature and potential mutagenicity of many azo dyes, this release could result in significant human and/or environmental health hazards. This research focused on the fate, as well as the mutagenicity and toxicity, of selected azo dyes and their metabolites, in suspended growth systems, when subjected to treatment in anaerobic and aerobic processes. The Ames Test and the Microtox™ test were performed to determine the mutagenicity and toxicity, respectively, associated with these compounds.; The azo dyes selected for this research were Eriochrome Black T, Eriochrome Blue Black B, Eriochrome Black A, and Palatine Chrome Black. These dyes were selected because all are monoazo dyes with a single sulfonate group. In addition, these dyes compliment each other structurally in that Eriochrome Black T and A contain the nitro group while the others lack this group. Also, Eriochrome Black T and Blue Black B are formed using alpha-naphthol while the other two are formed using beta-naphthol.; Findings show that none of the four dyes were readily aerobically biodegradable. In general, the dyes Eriochrome Blue Black B and Palatine Chrome Black were significantly adsorbed to the anaerobic sludge. Eriochrome Black T was apparently degraded in the anaerobic sludge, but not mineralized, releasing mutagenic metabolites into solution. The mutagenicity associated with these metabolites was removed once exposed to aerobic treatment in a combined anaerobic/aerobic treatment system. Eriochrome Black A, while initially absorbed to the anaerobic sludge, broke down over time releasing toxic and mutagenic metabolites from the sludge. All of the dyes demonstrated mutagenic activity in the Ames test. The presence of a nitro group on the dye increased the mutagenic response elicited in the Ames test. Metabolites from Eriochrome Black A and Palatine Chrome C elicited toxic responses in the Microtox™ test. Since azo dye mutagenicity and toxicity appears to be related to dye structure, this information could be used to create non-mutagenic azo dyes.