Degradation of Azo Dyes by Environmental Microorganisms and Helminths

Abstract

The degradation of azo dyes by environmental microorganisms, fungi, and helminths is reviewed. Azo dyes are used in a wide variety of products and can be found in the effluent of most sewage treatment facilities. Substantial quantities of these dyes have been deposited in the environment, particularly in streams and rivers. Azo dyes were shown to affect microbial activities and microbial population sizes in the sediments and in the water columns of aquatic habitats. Only a few aerobic bacteria have been found to reduce azo dyes under aerobic conditions, and little is known about the process. A substantial number of anaerobic bacteria capable of azo dye reduction have been reported. The enzyme responsible for azo dye reduction has been partially purified, and characterization of the enzyme is proceeding. The nematode Ascaris lumbricoides and the cestode Moniezia expunsa have been reported to reduce azo dyes anaerobically. Recently the fungus Phanerochaete chrysosporium was reported to mineralize azo dyes via a peroxidation-mediated pathway. A possible degradation pathway for the mineralization of azo dyes is proposed and future research needs are discussed.

Decolourisation of Acid Violet 7 with complex pellets of white rot fungus and activated carbon

“…There are at least 3000 azo dyes used in industries for various purposes [1]. Although they do not generally display acute toxicity, azo dyes are regarded as water pollutants because of their high colour intensity and possible mutagenesis in the environment [2,3]. Up to 10±15% of the amount of synthetic dyes produced annually is discharged with aqueous ef¯u-ents and most of them are resistant to degradation in conventional biological treatment process [4].…”

Comparison of white-rot fungi cultures for decolorization of textile dyestuffs

“…Some anaerobic microorganisms can biodegrade dyestuffs by azoreductase activity. However, the ef¯uent at the end of biodegradation of dyestuffs could be toxic [6,7]. Besides, upon exposure of the anaerobic degradation products to oxygen, reverse colorization may take place [8].…”

Single Strand DNA Breaks in Human Lymphocytes Exposed to para-Phenylenediamine and its Derivatives

“…Many azo dyes used by the industry also contain the p-phenylenediamine moiety (Chung et al 1993(Chung et al , 1995. After azo reduction of these dyes by environmental or intestinal microorganisms, PPD may be released (Chung et al 1993). When PPD is ingested, it will be absorbed and redistributed to target to exert its effect (Chen et al 2006).…”