Researchers demonstrated that laccase-dependent elimination of synthetic azo dyes reduces toxicity of these compounds. This promising feature can be utilized in wastewater treatment and reduce the harmful effects of the dyes on human health
Synthetic dyes are man-made colorant agents increasingly being used in textiles, papers, cosmetics, pharmaceutical industries, leather dyeing, color photography and food industries. Despite their ubiquitous use, most synthetic azo dyes are harmful because of their toxic, mutagenic and carcinogenic nature. Additionally, these dyes have been shown to prevent the growth of plants critical for the well-being of numerous ecosystems. As such, physical, chemical and biological techniques have been extensively studied for the removal of dyes from wastewater. Among the biological methods are laccases. Laccases are multicopper-containing oxidases derived from plants, fungi or bacteria, and demonstrate the ability to eliminate a wide variety of synthetic dyes.
A report published in the Journal of Environmental Health Science and Engineering investigated whether a fungal-derived laccase eliminates and reduces the toxic effects of 6 azo dyes: acid orange 67, basic red 18, basic yellow 28, disperse yellow 79, direct yellow 107 and direct black 166. To test this, six different bacterial suspensions were incubated with the dyes alone, or the dye in combination with laccase. Bacterial growth inhibition was then measured, where lower growth was indicative of higher toxicity. The authors concluded that laccase reduced toxicity of all six synthetic azo dyes. Moreover, it was demonstrated that laccase efficiently eliminated (decolourized) all dyes tested. The laccase-induced decolourization and removal of the dyes was enhanced in conditions with a pH of 5.0 (acidic) and temperature of 50-70 ºC. In addition, when used in the presence of mediators like HBT (1-hydroxyben zotriazole), laccase-induced decolourization was enhanced.
The toxicity of synthetic azo dyes poses a problem to human-wellbeing and the environment. Consequently, mechanisms for their elimination are needed to mitigate the harmful effects of these ubiquitously-used compounds. In this study, Laccases have been demonstrated as potent new tools in the reduction of synthetic azo dye toxicity. As, such these multicopper-oxidases warrant further investigation and are likely to be employed in commercial treatment of wastewater contaminated with azo dyes and other toxic compounds.
Written By: Haisam Shah