What Problem We Are Trying To Solve
Polychlorinated biphenyls, or PCBs, are harmful compounds that were used in the manufacturing of electrical equipment and hydraulics. The PCBS involved in these processes were often expelled as waste, allowing them to contaminate rivers and soil near factories. However, after the discovery of their adverse effects, including many types of cancers, they were prohibited in 1979. This did not stop the negative effects they have on communities and wildlife as PCBs can take more than a year to break down in water and even longer in soil.
About PCBs
PCBs consist of carbon, hydrogen, and chlorine atoms. The number of chlorine atoms and their location in a PCB molecule determines many of its physical and chemical properties[1]. PCBs are generally unreactive due to their aromaticity. Although PCBs are no longer produced in the U.S., they are still in use in closed systems (e.g., electrical transformers) and broadly distributed[2]. PCBs’ can be distributed across air and surfaces because of their octanol/air partition coefficient. Because of this phase-changing, PCBs can contaminate many surfaces[2].
There are 209 different PCB congeners (single, unique well-defined chemical in the PCB category). PCBs are typically insoluble in water but soluble in nonpolar organic solvents and biological lipids[3]. The relative levels of PCBs present change over time. These changes may greatly alter the toxicity of the resultant mixture[2].
How PCBs Cause Harm
PCBs take a very long time to break down due to their stable chemical structure. They bioaccumulate in the fatty tissues of fish and travel up the food chain, eventually moving up to larger animals and humans. Once in the wild, fish and other animals can become contaminated by ingesting PCBs and in fact make the molecules even more toxic and cancer causing[1]. PCBs alone are estimated to wipe out 10 out of 19 orca species within the next century [4]. PCBs dissolve in both fat and milk; mother orcas can pass up to 70% of their PCB levels to calves.
Most people and animals have a small amount of PCBs in their bloodstream and testing can be done on the red blood cells to measure PCB levels in humans[5]. Although low levels of exposure do not suggest immediate effects on one’s health, these levels can easily accumulate. Its presence in water can be compared to that of mercury. They both exist in upwards of 20% of tested sites[6]. A campus in the Monroe School District was found to contain a presence of PCBs[7]. Although this presence was not large enough to exceed EPA guidelines, the effects still took a toll on the students and teacher’s health. Symptoms included weakness, vomiting, rashes, headaches, memory loss, metabolic disorders, and even cancer. This could be caused by PCB levels combined with other harmful substances such as asbestos or radon. The EPA ordered a cleanup of the contaminated light fixtures within the school, but the damage that the PCBs have caused is irreversible.
Use and Regulation
PCBs were added to a variety of materials due to their low flammability, high boiling point, and stability. This makes them useful for many different industries. For example, they can prevent fires from spreading on naval ships. They were used in coolants/lubricants, capacitors and transformers, plastics, rubbers, and paints.After scientists around the globe realized PCBs have harmful effects to human life, Congress passed the Toxic Substances Control Act (TSCA) to ban the production of these substances in 1979. Ever since, the U.S. has had very stringent regulations on the acceptable levels of PCBs in commercial buildings or even schools.
The Chesapeake Bay Watershed Agreement was signed by watershed states spanning from New York to West Virginia to protect the Bay. But “84% of the Chesapeake Bay’s tidal segments are partially or fully impaired by toxic contaminants,” including PCBs[8]. Despite remediation attempts by local and state governments, water quality standards in the Bay are decreasing and PCB contamination affects most or all tidal tributaries feeding into the Bay.
In the Hudson River, between 1947 and 1977 General Electric deposited millions of pounds of PCBs into a 200 mile region of the Hudson[9]. Surface sediments throughout the River have PCB levels higher than the threshold levels and there have been reproductive health impairment in minks and otters, both predators. By 1984, the Environmental Protection Agency classified 200 miles of the Hudson River - from Hudson Falls to Manhattan - as a Superfund site, meaning it was one of the United States’ most contaminated environments[9].
Importance
The communities around both parts of our team, Baltimore and New York, rely on large bodies of water for economic and social life. The dangers and prominence of PCBs caused our team to want to take action against PCB pollution. Even though PCBs have been banned for almost 50 years, many waterways, including those around New York and Baltimore, are polluted by over a million tons of PCBs. Therefore, we chose to create a new way to detect and degrade PCBs for our iGEM project. Some current solutions for PCB removal include land burial, which only displaces PCBs instead of removing the contamination, and incineration, which can create even more carcinogens. PCBs are naturally degraded by the Pseudomonas, Burkholderia, Comamonas, Rhodococcus and Bacillus bacteria [10].
Biological transformations of PCBs are through anaerobic dechlorination, aerobic microbial degradation, and a combination of transformation of anaerobic dechlorination and aerobic degradation[11]. While systems similar to the one we aim to create already exist, they are expensive and difficult to use. Our goal is to make a new solution that is cheap and easily accessible to anyone. This way, clean and safe water can be available to everyone who might be at risk of coming into contact with these dangerous chemicals.
References
[1] Environmental Protection Agency. (2022, June 5). Learn about Polychlorinated Biphenyls (PCBs). EPA. Retrieved October 13, 2022, from https://www.epa.gov/pcbs/learn-about-polychlorinated-biphenyls-pcbs
[2] Hornbuckle, K., & Robertson, L. (2010). Polychlorinated biphenyls (PCBS): Sources, exposures, toxicities. Environmental Science & Technology, 44(8), 2749–2751. https://doi.org/10.1021/es100801f
[3] Centers for Disease Control and Prevention. (2022, August 15). Toxicological profiles. Toxicological Profiles. Retrieved October 13, 2022, from https://www.atsdr.cdc.gov/toxprofiles/tp17-c4.pdf
[4] Yong, E. (2018, September 27). The lingering curse that's killing Killer Whales. The Atlantic. Retrieved October 13, 2022, from https://www.theatlantic.com/science/archive/2018/09/pcbs-are-killing-killer-whales/571474
[5] Devs, B. (2021, September 21). HOW TO MEASURE AND TEST FOR PCBS. Retrieved October 13, 2022, from https://www.chemservice.com/news/how-to-measure-and-test-for-pcbs
[6] Freitag, A. (2010, June 16). Why Mercury and PCBS? Southern Fried Science. Retrieved October 13, 2022, from https://www.southernfriedscience.com/why-mercury-and-pcbs/
[7] Ramadan, L. (2022, January 23). Toxic PCBs festered at a Monroe school for eight years as students, teachers grew sicker. The Seattle Times. Retrieved from https://www.seattletimes.com/seattle-news/times-watchdog/toxic-pcbs-festered-at-a-monroe-washington-school-as-sky-valley-students-teachers-grew-sicker/
[8] Toxic contaminants policy and prevention. Chesapeake Progress. (n.d.). Retrieved October 13, 2022, from https://www.chesapeakeprogress.com/clean-water/toxic-contaminants-policy-and-prevention
[9] Petrequin, J. (2022, April 12). Report: Hudson River PCBS caused $11.4B in damages. NEWS10 ABC. Retrieved October 13, 2022, from https://www.news10.com/health/report-hudson-river-pcbs-caused-11-4b-in-damages
[10] Jing, R., Fusi, S., & Kjellerup, B. V. (2018). Remediation of polychlorinated biphenyls (PCBS) in contaminated soils and sediment: State of knowledge and Perspectives. Frontiers in Environmental Science, 6. https://doi.org/10.3389/fenvs.2018.00079
[11] Xiang, Y., Xing, Z., Liu, J., Qin, W., & Huang, X. (2020). Recent advances in the biodegradation of polychlorinated biphenyls. World Journal of Microbiology and Biotechnology, 36(10). https://doi.org/10.1007/s11274-020-02922-2