Azo dyes are a class of compounds containing the azo (R–N=N–R') functional group, and are widely used colouring agents in consumer goods, especially in the leather and textile industries.
However, the use of azo dyes has sparked serious health concerns in recent years – mostly attributed to reductive cleavage of the azo bond, which can lead to harmful breakdown products, including a range of aromatic amines.[1] The toxicity, carcinogenicity and potential mutagenicity of these aromatic amines to humans, as well as their potential toxicity to aquatic organisms, has accelerated the need for rigid control measures.
The risk presented by azo dyes has resulted in numerous countries – including India, USA and Europe – banning their use. For example, EU Commission Regulation (EC) No 1907/2006 (later amended to 552/2009 – Annex XVII) restricts the use of azo dyes that can form any of the 22 named aromatic amines that are classified as proven or suspected human carcinogens. The regulations state that azo dyes, which release one or more of the classified compounds in concentrations greater than 30 mg/kg, must not be used in leather and textile consumer products that may come into direct and prolonged contact with human skin or the oral cavity.[2]
Nevertheless, azo dyes are still appealing to the textile industry since they offer a wide spectrum of colours, are inexpensive to prepare and simple to use – meaning that robust standard methods are required to ensure compliance with regulations.
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