Genotoxic and carcinogenic products arising from reductive transformations of the azo dye, Disperse Yellow 7

Selected aromatic azo and benzidine based dyes are priority compounds under the Government of Canada's Chemical Management Plan (CMP) for environmental risk assessments. Organic compounds undergo chemical and biological transformations when they interact with environmental matrices and biotic species; identifying the transformation products is thus a critical component of the risk assessment process. Here, we used zero valent iron (ZVI) to initiate the reduction of the diazo compound dye Disperse Yellow 7 (DY 7). Using state-of-the-art accurate mass Liquid Chromatography-Quadrupole Time of Flight-Mass Spectroscopy (LC-QToF-MS), four transformation products were conclusively identified, while a fifth product was tentatively ascertained. The conclusively established transformation products included p-phenylenediamine (p-PDA, a known genotoxin), 4-aminoazobenzene (4-AAB, a category 2 carcinogen) and 4-aminobiphenyl (4-ABP, a category 1 human carcinogen). 4-ABP is thought to form via a benzidine rearrangement; this is the first report of DY 7 undergoing a benzidine rearrangement. Given the importance of reduction processes in the metabolism of organic contaminants by aquatic species, we used LC-MS/MS to analyze sediment samples that had been generated previously upon exposure of Western clawed frogs (Silurana tropicalis) to DY 7 (at exposure levels where cellular stress was observed in S. tropicalis). We found p-PDA, 4-AAB, and 4-ABP were present in all exposures, but not in any of the sediment controls, demonstrating that upon release of DY 7 to the aquatic environment, sediment dwelling organisms will metabolize DY 7 to generate known (and suspected) human carcinogens, including through a previously unreported in vivo benzidine rearrangement to produce 4-ABP.