Polychlorinated Biphenyls (PCBs): Environmental Fate, Challenges and Bioremediation

The bioremediation of the typical persistent organic pollutants (POPs) by microalgae-bacteria consortia: A systematic review

With industrialisation and the rapidly growing agricultural demand, many organic compounds have been leaked into the environment, causing serious damage to the biosphere. Persistent organic pollutants (POPs) are a type of toxic chemicals that are resistant to degradation through normal chemical, biological or photolytic approaches. With their stable chemical structures, POPs can be accumulated in the environment, and transported through wind and water, causing global environmental issues. Many researches have been conducted to remediate POPs contamination using various kinds of biological methods, and significant results have been seen. Microalgae-bacteria consortium is a newly developed concept for biological technology in contamination treatment, with the synergetic effects between microalgae and bacteria, their potential for pollutants degradation can be further released. In this review, two types of POPs (polychlorinated biphenyls and polycyclic aromatic hydrocarbons) are selected as the targeted pollutants to give a systematic analysis of the biodegradation through microalgae and bacteria, including the species selection, the identification of dominant enzymes, as well as the real application performance of the consortia. In the end, some outlooks and suggestions are given to further guide the development of applying microalgae-bacteria consortia in remediating POPs contamination. In general, the coculturing of microalgae and bacteria is a novel and efficient way to fulfil the advanced treatment of POPs in soil or liquid phase, and both monooxygenase and dioxygenase belonging to oxygenase play a vital role in the biodegradation of PCBs and PAHs. This review provides a general guide in the future investigation of biological treatment of POPs.

Concentration and sources of persistent organic pollutants within the vicinity of a scrap-iron smelting plant: Seasonal pattern and health risk assessment

Polychlorinated biphenyls (PCBs) are a class of ubiquitous and significant synthetic organic chemicals that pose deleterious threats to the environment and human health. This study examined the concentration, indoor-outdoor and seasonal change, sources, and health effects of PCBs in particulate-bound dust near a scrap iron recycling plant. PCBs levels were determined in samples using gas chromatograph mass spectrometer. The results indicated that 5 Cl atoms PCB constituted the majority of PCBs (41% overall), contributing 43% during the rainy season and 39% during the dry season. Dioxin-like PCBs (DLPCBs) contributed 38% during the rainy season and 33% during the dry season. In addition, DLPCB accounted for 26% and 40% of indoor and outdoor PCB emissions, respectively. Iron and steel production were identified as the highest identified contributing sources, accounting for 76% of PCB emissions in the rainy season, while plastic combustion had the highest contribution in the dry season, accounting for 44% of PCB emissions. Incremental Lifetime Cancer Risk assessment showed ingestion as the main exposure pathway for children and adults during the two seasons (74.42% and 58.24%, respectively), followed by dermal exposure, while inhalation had the least contribution. A multifaced approach involving relevant agencies, the industry, and the community is required to reduce exposure.

Bacterial enzymatic degradation of recalcitrant organic pollutants: catabolic pathways and genetic regulations

Contamination of soil and natural water bodies driven by increased organic pollutants remains a universal concern. Naturally, organic pollutants contain carcinogenic and toxic properties threatening all known life forms. The conventional physical and chemical methods employed to remove these organic pollutants ironically produce toxic and non-ecofriendly end-products. Whereas microbial-based degradation of organic pollutants provides an edge, they are usually cost-effective and take an eco-friendly approach towards remediation. Bacterial species, including Pseudomonas, Comamonas, Burkholderia, and Xanthomonas, have the unique genetic makeup to metabolically degrade toxic pollutants, conferring their survival in toxic environments. Several catabolic genes, such as alkB, xylE, catA, and nahAc, that encode enzymes and allow bacteria to degrade organic pollutants have been identified, characterized, and even engineered for better efficacy. Aerobic and anaerobic processes are followed by bacteria to metabolize aliphatic saturated and unsaturated hydrocarbons such as alkanes, cycloalkanes, aldehydes, and ethers. Bacteria use a variety of degrading pathways, including catechol, protocatechuate, gentisate, benzoate, and biphenyl, to remove aromatic organic contaminants such as polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and pesticides from the environment. A better understanding of the principle, mechanisms, and genetics would be beneficial for improving the metabolic efficacy of bacteria to such ends. With a focus on comprehending the mechanisms involved in various catabolic pathways and the genetics of the biotransformation of these xenobiotic compounds, the present review offers insight into the various sources and types of known organic pollutants and their toxic effects on health and the environment.

Analysis of polychlorinated biphenyls (PCBs) in dairy products by modified QuEChERS/GC-QqQ-MS/MS method: A risk assessment study

Polychlorinated biphenyls (PCBs) are harmful chemicals that are persistent in the environment and can accumulate in the food chain. The purpose of the present research was to assess non-dioxin-like polychlorinated biphenyls (NDL-PCBs) in some dairy products (yogurt, doogh, and kashk) using modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) technique and gas chromatography-triple-quadrupole mass spectrometry (GC-QqQ-MS/MS) method and risk assessment study. The LOQs (limit of quantifications), LODs (limit of detections), recovery, and RSD for the PCB analytes were 0.180-0.360, 0.06-0.12 ng/g fat, 97.45-102.63%, and 6.33-8.86%, respectively. The results revealed that the mean concentrations of Ʃ6-NDL-PCBs in samples were 15.17 ± 3.44 ng/g fat, which was lower than the standard level established by European Union (EU, 40 ng/g fat). The maximum mean level was PCB 180 (9.98 ± 2.04 ng/g fat) and the minimum mean level of PCBs in samples was PCB 28 (0.09 ± 0.06 ng/g fat). Also, results showed that kashk samples had a maximum mean level of 6-NDL-PCBs (18.66 ± 2.42 ng/g fat) and doogh samples had a minimum mean level of 6-NDL-PCBs (12.21 ± 2.22 ng/g fat). The mean level of 6-NDL-PCBs in yogurt samples was 14.65 ± 2.02 ng/g fat. The heat map results showed the correlation between the spectral indices of 6-NDL-PCBs in different dairy products. According to the Monte Carlo method, risk assessment was done using calculating the Estimated Daily Intake (EDI) and Incremental Life Cancer Risk (ILCR). The EDI values of 6 NDL-PCBs based on the 95th percentile in yogurt, doogh, and kashk were 14.3, 1.49, and 0.5 ng/kg.day, respectively. Considering that the contaminant level in the samples is lower than the EU limit, it can be concluded that dietary exposure to 6 NDL-PCBs may not pose a risk to the health of consumers.

Comparative study of single cultures and a consortium of white rot fungi for polychlorinated biphenyls treatment

AIMS

To evaluate the mycoremediation of polychlorinated biphenyls (PCBs) by either single cultures or binary consortia of Pleurotus pulmonarius LBM 105 and Trametes sanguinea LBM 023.

METHODS AND RESULTS

PCBs tolerance, removal capacity, toxicity reduction and ligninolytic enzyme expression were assessed when growing single culture and binary consortium of fungus in 217 mg l^-1 of a technical mixture of Aroclor 1242, 1254 and 1260 in transformer oil. A decrease in tolerance and variation in ligninolytic enzyme secretion were observed in PCB-amended solid media. Pleurotus pulmonarius LBM 105 mono-culture was able to remove up to 95·4% of PCBs, whereas binary consortium and T. sanguinea LBM 023 could biodegrade about 55% after 24 days. Significant detoxification levels were detected in all treatments by biosorption mechanism.

CONCLUSIONS

Pleurotus pulmonarius LBM 105 in single culture had the best performance regarding PCBs biodegradation and toxicity reduction. Ligninolytic enzyme secretion changed in co-culture.

SIGNIFICANCE AND IMPACT OF THE STUDY

The evaluation of PCBs bioremediation effectiveness of basidiomycetes consortium in terms of PCB removal, toxicity and ligninolytic enzyme production to unravel the differences between using individual cultures or consortium has not been reported. The results from this study enable the selection of P. pulmonarius LBM 105 mono-culture to bioremediate PCBs as it showed higher efficiency compared to binary consortium with T. sanguinea LBM 023 for potential decontamination of PCB-contaminated transformer oil.

Recent advances in the biodegradation of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are typical lasting organic pollutants. Persistence and recalcitrance to biodegradation of PCBs have hampered the transformation of PCB congeners from the environment. Biological transformation of polychlorinated biphenyls could take place through anaerobic dechlorination, aerobic microbial degradation, and a combination of transformation of anaerobic dechlorination and aerobic degradation. Under anaerobic conditions, microbial dechlorination is an important degradation mode for PCBs, especially high-chlorinated congeners. The low-chlorinated compounds formed after reductive dechlorination could be further aerobically degraded and completely mineralized. This paper reviews the recent advances in biological degradation of PCBs, introduces the functional bacteria and enzymes involved in the anaerobic and aerobic degradation of PCBs, and discusses the synergistic action of anaerobic reduction and aerobic degradation. In addition, the different ways to the microbial remediation of PCBs-contaminated environments are discussed. This review provides a theoretical foundation and practical basis to use PCBs-degrading microorganisms for bioremediation.

Assessment of Biodegradation Efficiency of Polychlorinated Biphenyls (PCBs) and Petroleum Hydrocarbons (TPH) in Soil Using Three Individual Bacterial Strains and Their Mixed Culture

Biodegradation is one of the most effective and profitable methods for the elimination of toxic polychlorinated biphenyls (PCBs) and total petroleum hydrocarbons (TPH) from the environment. In this study, aerobic degradation of the mentioned pollutants by bacterial strains Mycolicibacterium frederiksbergense IN53, Rhodococcus erythropolis IN129, and Rhodococcus sp. IN306 and mixed culture M1 developed based on those strains at 1:1:1 ratio was analyzed. The effectiveness of individual strains and of the mixed culture was assessed based on carried out respirometric tests and chromatographic analyses. The Rhodococcus sp. IN306 turned out most effective in terms of 18 PCB congeners biodegradation (54.4%). The biodegradation index was decreasing with an increasing number of chlorine atoms in a molecule. Instead, the Mycolicobacterium frederiksbergense IN53 was the best TPH degrader (37.2%). In a sterile soil, contaminated with PCBs and TPH, the highest biodegradation effectiveness was obtained using inoculation with mixed culture M1, which allowed to reduce both the PCBs (51.8%) and TPH (34.6%) content. The PCBs and TPH biodegradation capacity of the defined mixed culture M1 was verified ex-situ with prism method in a non-sterile soil polluted with aged petroleum hydrocarbons (TPH) and spent transformer oil (PCBs). After inoculation with mixed culture M1, the PCBs were reduced during 6 months by 84.5% and TPH by 70.8% as well as soil toxicity was decreased.