Abstract
The present work investigates the occurrence of the Acid Black 210 (AB210) dye and its subproducts in the tannery industry by analytical techniques. The AB210 is an important dye characterized by three azo groups as a chromophore and is one of the most used azo dyes in the tannery industry. The stability of AB210 in front of chlorination, sunlight exposition, and ambient conditions was investigated, as well as its occurrence and degradation products in the tannery wastewater. The stability study of AB210 showed a decrease in dye concentration of up to 45% after 14 days at room temperature. The exposure of the AB 210 by a solar simulator for 3 h showed discoloration of the dye. Furthermore, the chlorination of the AB210 caused a reduction of 25% in the intensity of the absorption band at the visible region after 300 s of treatment with sodium hypochlorite (NaClO). Studies based on high-performance liquid chromatography (HPLC-DAD), liquid chromatography-mass spectrometry (LC-MS/MS), and nuclear magnetic resonance (NMR) have indicated the occurrence of several harmful compounds such as benzene, cresol, naphthalene, phenol, 2-naphthylamine, and phenylacetic acid, and three aromatic amines, 2-naphthylamine, 2,6-dimethylaniline and 4-nitroaniline from the tannery industry. The cytotoxicity assay showed toxicity for the samples stored for a long period. Thus, the immortalized human keratinocyte (HaCAT) and 3T3 cells assays for the AB210 stored for 14 days showed 70% cell death in both strains evaluated. Our results demonstrated that the AB210 degradation is a great environmental concern due to increased toxicity for the body of living beings, especially for humans, as their biotransformation produces harmful compounds such as amines, which have been widely condemned by the International Agency for Research on Cancer.
Highlights
The tanyard process is one of the most important system involved in the leather industry (Bień et al, 2017)
The three azo groups acting as chromophore centers presented UV-Vis spectra marked for three bands of maximum absorbance at 403, 458, and 612 nm for 50 mg L−1 of Acid Black 210 (AB210) in aqueous solution, as shown in Figure 2A
The results showed a decrease in the absorbance from 0.66 to 0.43 after 14 days, which represents a decrease in dye concentration up to 34% in the band intensity at 612 nm as shown in Figure 2A
Summary
The tanyard process is one of the most important system involved in the leather industry (Bień et al, 2017). The production of leather is one of the oldest procedures in the world, tannery wastewaters raise great concern due to the occurrence of high amounts of chemical additives used in regular processes, as: acids, chromium, dyes, salts, surfactants, and many others (Ortega et al, 2005) (Oral et al, 2007) (Paschoal et al, 2009) (Kurade et al, 2017) (Kurade et al, 2019). Dyes presented in tannery wastewaters constitute a substantial source of pollution, as they can be related to ecotoxicity, high chemical oxygen demand, and strong color content, which interferes with the aquatic biota. There is no indication regarding the subproducts generated in all these processes and there is an ecotoxicological concern about the possible products generated after the degradation of AB210
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