Identification of intermediates and ecotoxicity assessment during the UV/H2O2 oxidation of azo dye Reactive Orange 16

Degradation of azo dye Reactive Orange 16, a widely used textile dye, was carried out with UV light in the presence of H2O2. The experiments were conducted in the batch mode using low-pressure mercury lamps, emitting at 253.7 nm. Liquid-chromatography tandem mass spectrometry (LC/MS/MS) and high resolution mass spectrometry (FT-ICR) were employed in order to identify some of degradation products as well as to suggest possible degradation pathways. According to the mass spectrum characterization of RO16 dye and MS(n) fragmentation (up to MS(4)), its possible fragmentation pattern was proposed. The results revealed that degradation occurred mainly via hydroxylation, cleavage of the C‒S bond between the aromatic ring and the sulfonate group, cleavage of the azo bond, cleavage of the C‒N bond between azo group and naphthalene ring and aromatic ring opening. Toxicity test with marine photobacterium Vibrio Fisheri was performed to consider whether or not the UV/H2O2 treatment of RO16 dye results in the products with enhanced toxicity for aquatic life.