Abstract
There has been increased interest in the use of natural dyes for textile coloration as alternatives to synthetic dyes, due to the general belief that natural dyes are more environmentally friendly. However, natural dyes have poor affinity for textiles, which can lead to high dye levels in the resultant wastewater. While chlorine treatment has proven to be effective for dye wastewater disinfection and decolorization, this process can also lead to the formation of more toxic degradation products for certain synthetic dyes. On the other hand, little information is available regarding the ecotoxicity of natural dyes and their chlorination products. To advance knowledge in this area, madder was selected due to its historical importance and wide application in the textile industry. Specifically, we sought to characterize the chlorine-induced degradation products of an aqueous madder solution and to assess their ecotoxicity. The main component of the present madder sample was Alizarin (89.8%). Chlorination led to complete decolorization, and 2-hydroxynaphthalene-1,4-dione and phthalic anhydride were identified as key degradation products. Chlorination of madder decreased toxicity to Daphnia similis (microcrustacean) 10-fold and removed the toxicity to Raphidocellis subcapitata (algae), when compared to the parent dye.
Highlights
Natural dyes were the only source of color for textiles until the serendipitous formation of the dye Mauveine by William Perkins, in 1856 (Drivas et al 2011)
Results from HRMS analysis of the present madder dye sample indicated the presence of alizarin (m/z 239.03482) and purpurin (m/z 255.02980) as the major components (0), with 89.8% of the sample consisting of alizarin
Chlorination rapidly promoted dye decolorization, as evidenced by the disappearance of the absorption band centered at 430 nm (0A)
Summary
Natural dyes were the only source of color for textiles until the serendipitous formation of the dye Mauveine by William Perkins, in 1856 (Drivas et al 2011). Following this discovery, synthetic dyes soon became available worldwide, and by 1880 most natural dyes were replaced by synthetic dyes on a global scale (Drivas et al 2011; Yusuf et al 2017). Commercial synthetic dyes exhibited direct fiber affinity (cf. Figure 1B, high reproducibility of their shades, wide range of colors, and more cost-effective application methods (Samanta and Konar 2011)
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