## 6 Types and Mechanisms of Removing Xenobiotics from Water
### Types of Lacase- Assisted Removing Xenobiotics from Water
#### 6.1.4 Plasticizers
Na+ decreased LacB activity and stimulated LacA. LacA showed greater catalytic potential toward BPA as a substrate than LacB. LacA degraded BPA at a concentration of 20 mg/L at pH 5.5 over 5 h batch tests at a laccase concentration of 0.75 U/mL, with an efficiency of approx. 70%. Highly active and stable laccase was isolated from the spore cells of _Bacillus_ sp. GZB, a BPA-degrading bacterium. The _Bacillus_ sp. GZB strain was obtained from sludge collected from an electronic waste recycling facility in Guiyu, China. Complete degradation of BPA at a concentration of 10 mg/L was achieved after 30 h of incubation. Based on the identified intermediates, the pathway of BPA degradation by bacterial laccase was proposed. Due to the oxidation of BPA by laccase, phenoxy radicals were formed in the first step, and further oxidation or cleavage of the C-C bonds of the radicals resulted in the formation of various organic acids. During degradation, the toxicity of BPA, tested against _Photobacterium phoreum_, gradually decreased. The exceptional laccase resistance of _Bacillus_ sp. GZB to changes in temperature and pH is due to the structure of the spore cells, which can serve as a matrix in immobilization. This enables the use of laccase as a natural biocatalyst in wastewater treatment to remove the toxicity caused by BPA [237]. The accumulation of synthetic plastics is a serious problem for the environment and human health. The most commonly used homopolymer in the production of plastics is polyethylene (PE) [228; 229]. The rapid increase in plastic production and waste volumes requires the development of effective plastic waste management solutions [228]. Plastic waste in the environment is naturally broken down by photo-, bio- and thermo-oxidative depolymerization as well as friction [229]. Plastic products thrown into the environment terribly pollute water resources and pose a serious threat to aquatic and marine organisms [238; 239]. Biodegradation is necessary for water-soluble or water-immiscible polymers because they end up in water streams that cannot be recycled or incinerated [239]. Unfortunately, petroleum-derived (petro)polymers are extremely resistant to natural pathway biodegradation. tion. Their complete decomposition in the natural environment can take over 50 years [229]. The enzymatic degradation of plastics begins with the adsorption of enzymes on the polymer surface followed by the hydroperoxidation/hydrolysis of the bonds. The sources of enzymes that break down plastics can be found in microorganisms from various environments and in the digestive intestines of some invertebrates [229]. PE is a high molecular weight polymer linked by a C-C single bond [240]. PE is one of the most inert plastics, and its resistant nature is due to its high molecular weight, complex three-dimensional structure and hydrophobic properties that make it difficult for microorganisms to access [239]. [PERSON] indicated that lactose could affect polyethylene molecules by creating carbonyl groups and thus reducing the molecular weight of PE molecules [241]. Another example is the _T. harzianum_ increase and manganese peroxidase from landfill soil in the Shivamogga district which were able to degrade PE to form carboxylic acid groups, aldehydes, aromatic compounds, alcohols, esters, ethers and alkyl halides [239]. In the work of [PERSON] et al. (2022), recombinant lactose from _Acinetobacter baumanni_ Rd-H2 was obtained isolated from a grain and food storage pest [240]. The recombinant AbMCO enzyme led to the occurrence of basic structural changes on the surface of the PE film. The enzyme expressed in _E. coli_ showed good stability in the range of 30-45 \({}^{\circ}\)C, with an optimum temperature of 45 \({}^{\circ}\)C and optimum pH of 4.5. The bacterial treatment breaks the chain of the PE polymer, which reduces the molecular weight and increases the hydrophilicity of the PE polymer.