Fate of azo dyes in the environment: A physico-chemical basis for stability, bioavailability and partitioning among water, sediment and the biota.

摘要

Azo dyes are a class of organic compounds characterized by the presence of the azo linkage (-N=N-), and comprise 60% of all coloring agents in use today. Nearly 40,000 azo dyes are currently in commercial use, and as such, represent a significant number of manufacturing processes, products and by-products. Zollinger has estimated that the colorant release to the environment represents 15% of total world production, or approximately 128 tons per day. Once in the environment, dyes and dye related compounds may bind to sediment or biomass, or be transformed by physical, chemical or microbiological mechanisms. A significant class of environmental transformation products of azo dyes are the aromatic amines that result primarily from reductive cleavage of the azo bond in the biota. The significance of aromatic amine production in the biota is due to the fact that many of these compounds are known human carcinogens. Furthermore, our studies have shown that many of these products of reductive azo bond cleavage are significantly more bioavailable than their parent dye molecule. Azo bond length and electron density about the azo bond, as calculated by theoretical methods, allow prediction of the type of environmental transformation a dye molecule will undergo, as well as the tentative identification of the transformation products. This results in a predictive capacity that allows a more focussed approach to the characterization of the human health impact of azo dyes and aromatic amines by concentrating on those dyes that are subject to reductive azo bond cleavage.