## 6 Types and Mechanisms of Removing Xenobiotics from Water
### Types of Lacase- Assisted Removing Xenobiotics from Water
#### 6.1.1 Synthetic Dyes
Textile wastewater contains dyes mixed with various impurities in different ranges, such as metals, solvents, salts, surfactants and other chemicals [8; 19]. Biological decolorization of this wastewater is an ecological and cost-effective approach that does not generate secondary wastewater [11; 19; 197]. Lacases have found a particular application in the decolorization of dyes because they are able to oxidize both phenolic and nonphenolic compounds [197]. _Myrothecium verrucaria_ NFCCI 4363, a fungus isolated from soil contaminated with waste from the sugar industry, produces extracellular lactose capable of decolorizing wastewater containing azo, triarylmethane and nitro dyes. The enzyme showed maximum activity at pH 6 and 50 \({}^{\circ}\)C and did not significantly change its enzymatic activity in the presence of low concentrations of some metals and solvents (dichloromethane, acetonitrile and methanol). The enzyme without mediators decolorized triarylmethane dyes (bromothymol blue, bromocresol green and bromocresol purple) with an efficiency of about 80%. In the presence of ABTS as a mediator, the lacase discolored acid magenta by about 70% and crystal violet by about 58%. [PERSON] et al. (2021) suggest that the degree of dye decolorization by lacase depends mainly on the origin of the enzyme and the presence of mediators, metal ions, solvents and other compounds in the reaction mixture [198]. A single lacase with a molecular weight of 41 kDa was produced by the white rot fungus _Oudemansiella canarii_ EF72, an edible mushroom from _Agaricales_ (mushrooms) commonly found in the Atlantic rainforest, Amazon rainforest and Pantanal [199]. The enzyme showed a broad range of pH stability (from 3.0 to 8.0) for at least 6 h. Lacase decolorized Congo red by 80% in 24 h at 30 \({}^{\circ}\)C and pH 5.5. The azo dye Congo red is present in significant amounts in textile and paper industry effluents and has been reported to be carcinogenic to humans and toxic to humans [10]. The analysis of Congo red degradation products revealed that the lacase acts on the chromophore group of the dye and asymmetrically cleaves azo covalent bonds, causing effective fragmentation of the molecule and the formation of products with nitrification of the NH\({}_{2}\) group and loss of the SO\({}_{3}\) group. The nitrified and/or hydroxyl groups of the naphthalene derivatives identified in the reaction mixture were probably derived from the oxidation of the amino groups present in Congo red. In the last stage of degradation, the benzene ring opened, and a fully oxygenated compound with the formula C8H3N2O8 was formed. The native lacase treatment reduced toxicity by 92.5% after 24 h. In conclusion, _O. canarii_ lacase can be used in the bioremediation and detoxification of azo dyes. The lacase of spores of the halotolerant bacterium _Bacillus safensis_ S31, isolated from the soil of a chromite mine in Iran, showed the ability to decolorize various classes of dyes. The maximum activity of the enzyme was achieved at 30 \({}^{\circ}\)C and pH 5.0. The enzyme tolerated the presence of 10% solutions (\(v/v\)) of solvents, such as methanol, ethanol and acetone and most of the tested metal ions. Unlike many other lacases, NaN\({}_{3}\) at concentrations of 0.1 and 1 mM showed a slight inhibitory effect on enzyme activity (7.5%), which is important due to the fact that NaN\({}_{3}\) is a toxic substance found in textile industry wastewater and dyeing. The enzyme showed the highest decolorization efficiency in relation to malachite green (87%) in the presence of ABTS and in relation to reactive black 5 (75%) in the absence of ABTS. In conclusion, the research by [PERSON] et al. (2018) proved that B. safensis S31 spore lactose can be used for the bioremediation of textile wastewater containing a number of dyes due to its high tolerance to metals, salts, solvents and sodium azide [19].