## 6 Types and Mechanisms of Removing Xenobiotics from Water
### Types of Lacase- Assisted Removing Xenobiotics from Water  
#### 6.1.1 Synthetic Dyes  
There are about 10,000 different textile dyes, with a global production of more than 700,000 tonnes per year [8]. Dyes are present in many areas of human life. They have many applications, from the textile, tanning, cosmetic and food industries to medicine. The sources of synthetic organic dyes in aquatic environments are industry (including 20% of  
Figure 3: The main xenobiotics found in aquatic ecosystems. the pollution that comes from the textile industry) and households (food dyes, improperly disposed of unused medicines, hair dyes, cosmetics, household chemicals, e.g., shampoos, soaps and washing powders) [8; 191; 192]. The textile industry uses large amounts of drinking water to produce fibers and, thus, releases huge amounts of wastewater [192]. In 1865, while trying to produce quinine, [PERSON] unexpectedly synthesized purple, the first commercialized synthetic organic dye, which marked the beginning of the production of synthetic organic dyes on a global scale [10]. Currently, this market includes around 100,000 substances [8]. Dyes can be divided into natural and synthetic dyes. Synthetic dyes are easy and cheap to produce, come in a variety of colors and are durable, which makes them more widely used than natural dyes [192]. Synthetic organic dyes are divided into groups depending on their chemical structure (acridine, anthraquinone, azo, azine, diphenylmethane, indigoid, methine, nitro, nitroso, oxazine, phthalocyanine, thiazine, triphenylmethane and xanthene) and depending on their use (acidic, basic, direct, dispersive, fibrous, reactive, vat and pickle) [193]. An important feature of synthetic dyes used by the industry is their high resistance to external physical and chemical factors, such as solar radiation, large temperature changes or the presence of detergents and disinfectants in washing agents. This is also related to their poor biodegradability in the environment [106; 194; 192]. Among them, the most commonly used dyes are azo dyes, which are resistant to decomposition under the influence of temperature, light or acids and alkalis, which makes their removal from wastewater very difficult [19]. The disposal of approximately 4.5 million tonnes of dyes and their degradation products, a large part of which is highly toxic to living organisms, is a huge environmental problem and entails high costs, e.g., for the construction of the appropriate sewage treatment plant infrastructure [11]. A large amount of water used in industry and the loss of dyes during textile processes generate huge amounts of colored wastewater. The dyes present in wastewater absorb and reflect sunlight. Light penetration is limited, which disturbs the photosynthesis of aquatic flora, and consequently leads to a decrease in the amount of oxygen dissolved in the water. Synthetic organic dyes have a toxic effect not only on the flora but also on the fauna of aquatic ecosystems. In fish, dyes are absorbed through the gills and skin [195]. They are then distributed throughout the body and undergo metabolization. For example, azo dyes are degraded to carcinogenic aromatic amines by azoductase produced by intestinal microflora [196]. Compared to the parent form, a lot of these metabolites are more lipophilic than the starting material and, therefore, easily accumulate in the fat tissue of fish, for example, and remain in the weight of fish for longer. These mechanisms consequently lead to the bioaccumulation of dyes in the trophic chain [8; 11]. Due to their toxicity to living organisms, these dyes should be detoxified or eliminated (usually discolored) prior to discharge into the environment [19; 197]. Due to the complex structure of the dyes used and the complex composition of wastewater from various industries [9], physical, chemical and biological methods or a combination of several methods are used to remove dyes [197].