Can microbes munch up PCBs?
Mother Nature comes to the rescue once again.
Bioremediation
Living organisms can safely break down and eliminate waste and toxins. These naturally occurring microbial communities that reside in soil and water, can be selected for their abilities to degrade hydrocarbon molecules and even heavy metals. They eat up polluting compounds and convert them into environmentally benign components. And once their work is done, they die off and act as feed to the neighboring organisms.
A past newsletter discussed the critters that went after plastic waste. Wax worms were first discovered and then the bacteria in their gut doing the major work to breakdown these petroleum products.
Methodology : Nobel Prize winner using evolution to find enzymes
In another past newsletter I reported on how we search for, enrich and identify the ideal metabolic enzymes for these commercial endeavors.
“Frances Arnold pioneered the use of ‘directed evolution’ to create enzymes with improved and/or novel functions. The strategy involves iterative rounds of mutagenesis and then screening for proteins with improved functions. She and her colleagues used this strategy to create useful biological systems, metabolic pathways, genetic regulatory circuits, and even novel organisms.”
Baltimore Harbor watershed: PCB river dumping
Polychlorinated biphenyls (PCBs) contamination is widespread, especially in riverbed sludge, downstream from industrial dumping sites. University of Maryland environmental engineers and their collaborators researched ways to clean up the rivers pouring into the Chesapeake Bay and the Baltimore Harbor. Results are very encouraging, showing that indigenous microbes in this microcosm/niche adapted to metabolizing these pollutants, converting them into nontoxic by products.
Abstract: Sediment contamination is a major environmental issue in many urban watersheds and coastal areas due to the potential toxic effects of contaminants on biota and human health. Characterizing and delineating areas of sediment contamination and toxicity are important goals of coastal resource management in terms of ecological and economical perspectives. Core and surficial sediment samples were collected from an industrialized urban watershed at the East Coast of the United Stated and analyzed to evaluate the PCB contamination profile and toxicity resulting from dioxin-like PCBs as well as reductive dechlorination potential of indigenous PCB halorespiring bacteria through dechlorination activity assays. To support the experimental results an anaerobic dechlorination model was applied to identify microbial dechlorination pathways. The total PCB concentration in core samples ranged from 3.9 to 225.6 ng/g·dry weight (dw) decreasing with depth compared to 353.2 to 1213.7 ng/g·dw in surficial samples. The results of this study indicated an increase in PCB contamination over the last century as the industrial activity intensified. The toxicity resulting from dioxin-like PCBs was reduced up to 94% in core samples via 21 pathways resulting from the dechlorination model. Dechlorination rates in surficial sediment were between 1.8 and 13.2 · 10−3 mol% PCB116/day, while lower rates occurred in the core sediment samples. Dechlorination was achieved mainly through meta followed by para dechlorination. However, the rarer ortho dechlorination was also observed. Detection of indigenous PCB dechlorinating bacteria in the sediments and reduction of toxicity indicated potential for natural attenuation when point and nonpoint source PCBs in the urban watershed are controlled and PCB loading reduced. - D Kaya, et al.
In organochlorine chemistry, reductive dechlorination describes any chemical reaction which cleaves the covalent bond between carbon and chlorine via reductants, to release the chloride ions.
Microbial reductive dechlorination of polychlorinated biphenyls (PCBs) is regarded as an alternative approach for in situ remediation and detoxification in the environment. To better understand the process of PCB dechlorination in freshwater lake sediment, a long-term (108 weeks) dechlorination study was performed in Taihu Lake sediment microcosms with nine parent PCB congeners (PCB5, 12, 64, 71, 105, 114, 149, 153, and 170). Within 108 weeks, the total PCBs declined by 32.8%, while parent PCBs declined by 84.8%. PCB dechlorinators preferred to attack meta- and para-chlorines, principally para-flanked meta and single-flanked para chlorines. A total of 58 dechlorination pathways were observed, and 20 of them were not in 8 processes, suggesting the broad spectrum of PCB dechlorination in the environment. Rare ortho dechlorination was confirmed to target the unflanked ortho chlorine, indicating a potential for complete dechlorination. PCBs drove the shifts of the microbial community structures, and putative dechlorinating bacteria were growth-linked to PCB dechlorination. The distinct jump of RDase genes ardA, rdh12, pcbA4, and pcbA5 was found to be consistent with the commencement of dechlorination. The maintained high level of putative dechlorinating phylum Chloroflexi (including Dehalococcoides and o-17/DF-1), genus Dehalococcoides, and four RDase genes at the end of incubation revealed the long-term dechlorination potential. This work provided insights into dechlorination potential for long-term remediation strategies at PCB-contaminated sites. - L Xu et al
These organisms are found throughout the world’s sediment. Certainly, turning to Mother Nature’s methods are the best first steps when correcting industrial waste mismanagement. Monitored natural attenuation is a cost-effective and environmentally sustainable alternative for remediation of PCB-contaminated sediments compared to excavation and dredging, which can instead increase the exposure to PCBs due to resuspension.
The current go to method coming from politicians and bureaucrats, is dredging rivers and transporting the sludge via trucks through residential neighborhoods. There is NO basis what-so-ever to propose this!
Be educated and aware. First DO NO HARM.
REFERENCES
AK Awasthi et al. Environmentally sound system for E-waste: Biotechnological perspectives. Vol 1, November 2019, Pages 58-64 https://doi.org/10.1016/j.crbiot.2019.10.002
Chilean scientist plans to clean up mining with 'metal eating' bacteria (2021, October 9) https://phys.org/news/2021-10-chilean-scientist-metal-bacteria.html
D Kaya, et al. Assessment of PCB contamination, the potential for in situ microbial dechlorination and natural attenuation in an urban watershed at the East Coast of the United States. Science of The Total Environment, Vol 683, 2019, pp 154-165. https://doi.org/10.1016/j.scitotenv.2019.05.193.
L Xu et al. Long-Term Dechlorination of Polychlorinated Biphenyls (PCBs) in Taihu Lake Sediment Microcosms: Identification of New Pathways, PCB-Driven Shifts of Microbial Communities, and Insights into Dechlorination Potential. Environ. Sci. Technol. 2022, 56, 2, 938–950 https://doi.org/10.1021/acs.est.1c06057