## 6 Types and Mechanisms of Removing Xenobiotics from Water
### Mechanism of Removing Xenobiotics from Water
This strategy enabled the optimal flow of electrons between the substrate and the Cu T1 site of the active lactose center (neutral pH) and between the Cu T1 site and the trinuclear copper center (TNC) (acid pH). In almost 17 min, over 90% of the acetaminophen was converted to biologically inactive oligomers. The route of removing this compound from water with the use of lactose consisted of its oxidation with the formation of unstable free radicals, which then self-polymerized and precipitated in the  
Figure 4: Type of reaction catalyzed by lactose. reaction mixture. The dual pH optimization strategy, which achieved a higher rate of catalytic oxidation of substrates by lacase, consequently led to a much faster formation of acetaminophen dimers, trimers and tetramers than can naturally precipitate from water. [PERSON] et al. (2018) investigated the pathway of BPA degradation by the lacase of _Bacillus_ sp. GZB spores [237]. They noted the presence of BPA degradation intermediates, such as 4-hydroxybenzaldehyde, benzoic acid, 2-hydroxypropanoic acid, 2-methylbutanoic acid and 3-methylbutanoic acid. In other studies where other microorganisms were the source of lacases, the formation of other intermediates was identified. In the reaction of BPA with _T. villosa_ lacase, phenol and 4-isopropylphenol are formed [250]; with the immobilized _Trametes polyzona_ lacase on silica nanoparticles, phenol, 4-isopropylphenol and 4-hydroxyisopropylphenol [251]; with the lacase _T. versicolor_, ethylbenzene, p-xylene, cyclohexanone and 1-methyl-4-isopropyl-2-cyclohexenylene [252]; with the _Phaneroduete chrysosporium_ lacase, 2,2-methylenediphenyl, bis(4-hydroxyphenyl)methane and p-(benzyloxy)phenol [142]; and with the _T. versicolor_ lacase immobilized on the _Hippocampia communis_ spongin scaffolds, phenol, catechol and dimers [253]. In the case of BPA degradation by _Pseudomonas putida_ YC-AE1, the intermediates are stilbenol and hydroxyl derivatives of benzaldehyde, acetophenone, phenylacetate and phenacyl alcohol and hydroxylphenyl derivatives of propanol, propanol and propanoate [254]. In general, the biodegradation pathway of xenobiotics and the quantity and quality of the final products depends on the source of the lacase. The presence of mediators has a significant impact on the course of reactions catalyzed by lacase. Mediators are low molecular weight, water-soluble chemicals with a high redox potential (approx. 900 mV) that can act as one-electron shuttles between the enzyme and the compounds to be oxidized [106; 194]. The most effective mediators are N-heterocyclic compounds containing N-OH groups, such as hydroxybenzotriazole (HBT), 2,2,6,6-tetramethylpiperidin-1-yloxy (TEMPO), N-hydroxyphthaimide (HPI), N-hydroxyacetanilide (NHA) and violuric acid (VLA) [82]. The lacase-mediator system (LMS) has been used in the degradation of a wide range of contaminants as it induces the cleavage of oxidative bonds present in the structure of many types of xenobiotics dissected in this review [186; 255; 256; 257; 258; 259; 260]. In the studies by [PERSON] et al. (2016), using the crude lacase enzyme of the fungus _Coriolopsis gallica_ (BS54) [KJ412304] led to BPA degradation. The final product of BPA degradation was b-hydroxybutyric acid. Oxidative cleavage of BPA led to the formation of b-hydroxybutyric acid in the absence of HBT and tartaric acid in the presence of HBT. The final products were significantly different from those after treatment with BPA in the lacase/HBT system because the mediator is also oxidized to give other degradation and by-products. tartaric acid and pyroglutamic acid probably originated from the degradation of HBT. The formation of tartaric acid and \(\beta\)-hydroxybutyric acid could be the result of the oxidation of methyl groups on the propane moiety of the BPA molecule under the action of lacase.