Human economic activity and progressive urbanization pose a constant threat of environmental contamination with xenobiotics. The presence of cosmetic preservatives in water and soil samples, confirmed by numerous studies, is the cause of many undesirable processes that contribute to the disturbance of the biological balance, as well as the emergence of unfavorable changes at the ecosystem level. Due to the pollution of the natural environment with xenobiotics and their toxic properties, research on their removal has been developing on a large scale and is subject to great interest. However, few literature data that describe the elimination of these preservatives are available. The main way to remove preservatives from the environment is biodegradation carried out by micro-organisms. Biodegradation is a metabolism-dependent process of decomposition of xenobiotics into simpler compounds, taking place with the participation of extracellular and/or intracellular enzymes. This process often transforms the pollutants into simpler compounds that are typically less toxic than the parent compounds. In some cases, biodegradation leads to the mineralization of organic compounds and their degradation into carbon dioxide, water, and/or other inorganic products.

In the scientific literature, few works describe the potential of bacteria and fungi to effectively eliminate triclocarban, chloroxylenol, methylisothiazolinone, and benzalkonium chloride. It should be noted that the process of elimination of xenobiotics, in some cases, is not synonymous with their degradation and detoxification. Table 2 shows the biodegradation of the discussed biocides with the use of micro-organisms.

Research studies on the microbial degradation of triclocarban are numerous. The usage of sewage sludge, including of TCC residues in agriculture, poses a serious risk to the environment. The application of micro-organisms over composting biosolids could reduce the environmental risks of the use of sewage sludge as a fertilizer. The biodegradation of TCC via the composting of biosolids under high ventilation resulted in a reduction in xenobiotic concentrations by 83.1% over 16 days [143]. The immobilized microbial cells of Pseudomonas fluorescens (MC46) on biochar could be used for the effective purification of the sewage from TCC. The yield of the process carried out by immobilized P. fluorescens cells was much higher (79.80%) compared to the elimination of TCC by free P. fluorescens cells (42.12%) [144]. Similar results were obtained by Taweetanawanit et al., confirming that TCC was eliminated more efficiently by micro-organisms entrapped in barium alginate [145]. Moreover, researchers observed 3,4-dichloroaniline (34DCA), 4-chloroaniline (4CA), and aniline as by-products emerging via hydrolysis, dehalogenation, hydroxylation, and dechlorination, which were characterized by a lower toxicity than the parent compound. Subsequently, aniline may be transformed through deoxygenation into catechol and it is anticipated that catechol may thereafter undergo ring cleavage [145]. The same bacterial strain was used for the bioaugmentation of TCC-contaminated soil, with an elimination efficiency of 74–76%. P. fluorescens was able to remove TCC as a sole carbon source leading to its detoxification [146]. 34DCA, 4CA, and 4-chlorocatechol were reported to be the major metabolites present as a result of the bacterial degradation of TCC in Sphingomonas sp. YL-JM2C. The formed metabolites and parent compounds were too toxic for the tested strain and inhibited further biodegradation stopping at the level of 35% [147]. Three strains of Ochrobacterium sp. (MC22, TCC-1, and TCC-2) were also capable of triclocarban biotransformation under aerobic and anaerobic conditions [148,149,150,151]. Under aerobic conditions, strain MC22 was able to degrade TCC (initial concentration 9.40 mg L⁻¹) as a sole carbon and energy source with an efficiency of 78% within 6 days and to produce two intermediates 34DCA and 4CA, which were detoxified [148]. Similar metabolites were observed in strains TCC-1 and TCC-2; however, these micro-organisms were characterized by a higher tolerance to upper concentrations of TCC [149,150,151]. The anaerobic degradation of TCC by Ochrobacterium sp. was conducted with acetate as an electron donor. During transformation, 4CA and DCA were formed in all three strains. Only MC22 produced additional aniline [148,149,150]. Moreover, Yun et al. identified a protein accountable for TCC hydrolysis: amidase TccA [149].

Despite several reports describing the ability of micro-organisms to eliminate chloroxylenol, there is little research devoted to the identification of intermediate products formed during biodegradation and analyzing the mechanisms responsible for the course of these processes. Nowak et al. identified two fungal species capable of degrading chloroxylenol [124]. Cunninghamella elegans IM 1785/21GP and Trametes versicolor IM 373 degraded PCMX with similar efficiencies through different degradation pathways. C. elegans removed 70% of PCMX over 120 h of incubation, at an initial PCMX concentration of 25 mg L⁻¹, via the generation of two metabolites by dehalogenation, aromatic ring hydroxylation, and methyl group oxidation of the parent compound. T. versicolor demonstrated a 79% removal of PCMX over 120 h of incubation via ring opening during hydroxylation, dehalogenation, and oxidation, leading to the formation of three metabolites. The authors suggested that the two different enzyme systems are involved in the initial step of chloroxylenol degradation: cytochrome P450 mono-oxygenases in C. elegans and laccases in T. versicolor. Furthermore, the metabolites generated by tested micro-organisms have a lower toxicity than the parent compound. Among the micro-organisms demonstrating the ability to eliminate PCMX, the microscopic fungus Aspergillus niger was also described in which over 99% of PCMX loss (initial substrate content – 2 mg L⁻¹) was shown after 7 days of incubation [152]. Choi and Oh demonstrated that the removal efficiency of chloroxylenol by activated sludge depended on the initial concentration of xenobiotics [153]. PCMX at a concentration 5 mg L⁻¹ was eliminated over two months with a yield below 50%. In this research, the authors analyzed the impact of PCMX on the bacterial community structure and isolated two bacterial strains probably able to degrade PCMX: Sphingobium and Luteolibacter. Based on the literature data, the authors suggested that the biodegradation of PCMX occurs via dehalogenation and ring hydroxylation.

Little is known about the biodegradation of methylisothiazolinone by micro-organisms. Most often, only the initial stages of the biotransformation of this preservative are known. The few micro-organisms that exhibit the ability to metabolize MIT mainly include various species of filamentous fungi [20,154]. The ability of the ligninolytic fungus Phanerochaete chrysosporium to biodegrade this biocide over a 48 h incubation in liquid culture under aerobic conditions was described. The tested micro-organism was able to completely eliminate MIT at a concentration of 50 µg L⁻¹ and 30 mg L⁻¹ within 12 h [20]. Identified metabolites, formed during the degradation of MIT by P. chrysosporium were mono- and dihydroxylated methylisothiazolinon and N-methylmalonamic acid. The presence of hydroxylated derivatives indicates the involvement of hydroxylating enzymes in the biotransformation process. However, measurements of the activity of laccase, manganese peroxidase, lignin peroxidase, and cytochrome P450 did not confirm the involvement of these enzymes. It is noteworthy that the resulting MIT derivatives are less toxic than the parent compound against D. magna [20]. The process of the biodegradation of MIT by three strains of filamentous fungi, Trichoderma longibrachiatum FB01, Aspergillus niger FB14, and Fusarium solani FB07, occurs differently. Short-chain organic acids, such as tartaric acid, 2-oxobutanoic acid and acetic acid (T. longibrachiatum), malonic acid, 2-oxobutanoic acid, lactic acid, metoxiacetic acid, acetic acid (A. niger) and malonic acid, 2-oxobutanoic acid, propanoic acid, and acetic acid (F. solani) have been identified as metabolites of this preservative. The tested fungi were able to eliminate MIT in 16 h [154]. In both studies, stimulation of the growth of the tested micro-organisms was observed, which probably use this compound as a source of carbon and energy. So far, another pathway for the biodegradation of MIT by the microalgae Scendesmus sp. LX1 has been described. The algae completely removed MIT over 4 days and led to the cleavage of the ring by methylation and carboxylation [155].

Several reports have already described biologically mediated BAC degradation under laboratory conditions. The first report demonstrated the decomposition of BAC by 20 strains of Burkholderia cepacia bacteria. After an incubation period of 7 days, about 42.6% of BAC was eliminated. Benzyldimethylamine and benzylmethylamine were reported to be the metabolites present at the initial step of BAC degradation as a result of the cleavage of the C–alkyl-N bond. The authors identified two enzymes potentially responsible for C–N bond cleavage: amine oxidase and Rieske-type oxygenase. Moreover, eight catabolic enzymes involved in benzyldimethylamine degradation were identified and the complete degradation of the alkyl group of BAC was noted [156]. The isolation of BAC-degrading micro-organisms from a wide range of ecosystems has been described. Ertekin et al. isolated a strain highly resistant to BAC at a minimal inhibitory concentration of 1024 mg L⁻¹ [157]. The identified Pseudomonas sp. BIOMIG1 was able to eliminate BAC within 3 days by leading to complete mineralization. The evaluation of immobilization as a better method for BAC elimination was described by Bergero et al. [158]. The comparison of BAC biodegradation by planktonic cells of Aeromonas hydrophila MFB03 isolated from industrial WWTPs to its degradation by Ca-alginate-encapsulated cells showed that immobilization increased the efficiency of elimination and, after 48 h, led to the utilization of 90% BAC as a sole carbon and energy source. Due to physical protection, immobilized cells are more resistant to BAC than free cells. Similar results were obtained for Pseudomonas putida ATCC 12633 [159]. Moreover, the use of a microbial consortium formed by these two strains and encapsulated in Ca-alginate is the most efficient method for BAC removal [158]. N,N-dimethylbenzylamine was observed as the result of the C–alkyl-N bond cleavage of BAC-C16 by two isolates from marine sediments, Bacillus niabensis and Thalassospira sp. These bacteria were able to degrade up to 90% BAC over 7 days [160]. Oh et al. studied the biodegradation of BAC as a sole carbon and energy substrate using a microbial community stemming from estuarine sediment and a member of the genus Pseudomonas [161]. Within 12 h, 80% of BAC degradation was observed in a bioreactor inoculated with mixed cultures without the detection of biotransformation products. In order to obtain energy, P. nitroreducens, with the use of amine oxidases, causes the dealkylation of BAC and the formation of two aldehyde products: dodecanal and tetradecanal aldehydes. The obtained metabolites are characterized by a lower toxicity than the parent compound. The aerobic hydroxylation of BAC catalyzed by mono-oxygenase possibly occurs in an enriched community of Pseudomonas spp. The cleavage of the C–alkyl-N bond leads to the formation of benzyldimethylamine. The authors suggested that benzyldimethylamine could be biotransformed by debenzylation to benzoic acid and dimethylamine. These transformations lead to a reduction in acute toxicity (Microtox) [162]. The algal degradation of BAC via pure cultures has been explored in seawater microalgae, Tetrasemis suecica. The tested organisms were able to successfully eliminate BAC-C12 and BAC-C14 from seawater and produced water, with rates of about 100% and 54% within 14 days of incubation, respectively. Furthermore, twelve isomeric intermediates, which are characterized by a lower tendency to be adsorbed into sediments than the parent compounds, were found. The authors suggested that the chemical reactions involved in the biodegradation pathways were multiple hydroxylations followed by dehydration. Hydroxylated BAC-C12 and dihydroxylated BAC-C14 were the most intense by-products formed during BAC-C12 and BAC-C14 transformation, respectively [163].