Reduction of four bis-azo dyes by pig liver microsomal fraction in anaerobic conditions

The study of azo dyes degradation products and their harmfulness is an important topic because their diffusion in the environment is still a serious problem. We investigated the reduction by pig liver microsomal fraction of four bis-azo dyes, Acid Red 73, Acid Red 150, Direct Red 24, and Direct Red 28, in anaerobic condition. These complex molecules, different for position/nature of substituent groups and for the group interposed between the two azo bonds, allowed to investigate the correlation between substrate molecular structure and action of a subcellular fraction representative of the xenobiotic degradation by a living organism and the consequent possible appearance of harmful reaction products. Dyes were first carefully purified to eliminate interferences in the enzymatic assays. The reduction products were identified by gas chromatography/mass spectrometry. Acid Red 73 and Acid Red 150 were markedly reduced with production of harmful aromatic amines, while Direct Red 24 and Direct Red 28 were neither reduced to their synthesis amines nor to other amines. These results suggest that azo dyes with a benzidine derivative group are not degraded by microsomal fraction and therefore molecules with a similar structure could be classified with a lower risk index not producing any harmful catabolic product.