Potential Dye Pollutants and Its Toxicity Effects
The evaluation of the toxicity of dyes is very important, mainly due to the different effects that they cause in the environment and the organisms exposed to them. Dyes are considered as potential pollutants because of their toxicity effects . Generally dyes cause oral ingestion and inhalation, skin and eye irritation, and also carcinogenicity [39-41]. They impart colour to water which is visible to human eye and therefore, highly objectionable on aesthetic grounds. Not only this, dyes may cause micro-toxicity to fish and other organisms, also interfere with the transmission of light and upset the biological metabolism processes which cause the destruction of aquatic communities present in ecosystem . Additionally dyes also can cause severe damage to human beings such as dysfunction of kidney, reproductive system, liver brain and central nervous system . Generally basic dyes have been classified as toxic colorants . Basic dyes have high intensity of colours and the tinctorial value of basic dyes is very high, less than 1 ppm of dye is greatly visible in solution . Anthroquinone based dyes made from known carcinogens such as benzidine and other aromatic compounds are resistant to degradation due to their fused aromatic ring structure . Disperse dyes have good ability to bioaccumulation . Azo dyes are one of the more detrimental toxic classes because it is highly persistent in the aquatic environment, due to its chemical compositions, involving aromatic rings, azoic linkages and amino groups . Many studies have shown that reactive dyes can cause allergic dermatoses and respiratory diseases [46-49].
In addition to being toxic, dye effluents also contain chemicals that has been informed to cause carcinogenesis, mutagenesis or teratogenesis and respiratory toxicity to various organisms [50, 51]. As such it is important to treat coloured effluents for the removal of dyes. Therefore, focuses on specific methods and technologies for the removal of dye bearing wastewater is desired and is under constant development, with increasing attention being paid to the ecological effects of dyestuffs regarding its use.