Polychlorinated Biphenyls (PCBs)
What are PCBs?
Polychlorinated biphenyls (PCBs) are a group of high production industrial chemicals manufactured from 1929 until banned in the United States in 1979. The group includes 209 individual chemicals, known as congeners. Out of 209 possible PCB congeners, 120-140 are formed in commercial mixtures widely known under the US branded tradename Aroclor. Other commercial mixtures from different global producers include Clophen (Germany), Kanechlor (Japan), Phenochlor (France), and Ascarel (Brazil). Other congeners, known as incidental PCBs, can be formed as a by-product of another manufacturing process. Other congeners can also form from the breakdown of one PCB to form a different congener. PCBs are considered ubiquitous in the environment, meaning levels can be found in most environmental and biological compartments across the globe.
What are they used for?
The chemical and physical stability of PCBs were desirable in a variety of industries. There are several Aroclor products, distinguished by the percent chlorine by weight in the formulation. PCBs were used in transformers, capacitors, plasticizers, hydraulics, lubricants, and carbonless copy paper. PCBs are no longer manufactured, but there are products in use today that contain PCBs (e.g. transformers, caulking)(US EPA, 2019).
Where can they be found?
Levels of PCBs in the environment have been declining, but a measureable amount can be found in most environmental and biological samples. PCBs are lipophilic, meaning they have poor solubility in water and will distribute to other lipophilic substances, such as organic matter found in soils and sediments. In biological matrices, PCBs are distributed in the lipid (i.e. fat) components of tissue and blood serum. Higher concentrations of PCBs are found in humans compared to fish or birds, because the chemicals bioaccumulate up the food chain.
Why are they important?
Several national and international organizations, such as the International Agency for Research on Cancer (IARC), the Department of Health and Human Services (DHHS), and US Environmental Protection Agency (EPA) have classified PCBs as probable human carcinogens. PCBs are persistent organic pollutants (POPs), meaning they do not easily break down in the environment. A distinct sub-group of PCBs have toxicological effects similar to polychlorinated dibenzo-p-dioxins (PCDDs or dioxins) by binding to the Ah receptor. The spatial structural requirement results in 12 co-planar congeners, which are considered to be the most toxicologically relevant PCB congeners. These co-planar congeners are at very low levels in Aroclors and other commercial mixtures.
Chemistry Matters Consulting Services and Expertise
PCB contamination has been studied for over 50 years and will continue to be studied for years to come. The Chemistry Matters team has experience in evaluating exposure for humans and wildlife and are experts on PCB analysis and chemical fingerprinting. We have the litigation experience required for expert witness testimony and are actively involved in PCB related research by publishing in peer-reviewed journal articles and presenting at scientific conferences.
Figure 1: Each Aroclor formulation (e.g. Aroclor 1254, Aroclor 1242) has a different pattern of peaks. As the percent chlorine increases or decreases, the pattern is shifted right or left. A) GC-ECD chromatograms are instrument recorded peaks that display the retention time vs instrument response. Image: Aroclors on Rtx-PCB, courtesy of www.restek.com. B) Histograms use the PCB congener number and reported concentration values to improve data visualization. Image: Tabulated congener distributions (weight %), using: FRAME, G. M. 1997. Fresenius J Anal Chem, 357, 701-713.
Environmental Forensics of PCBs
The quantitation of PCBs in the environment requires the use of gas chromatography (GC). GC separates a chemical mixture into a series of peaks plotted on a chromatogram trace. The different formulations of Aroclors have a distinct pattern of peaks that elute from the GC instrument (Figure 1). Aroclor methods, such as US EPA Method 8082, quantifies a reduced set of PCBs and uses pattern matching to identify Aroclor concentrations in a sample. These relative amounts of Aroclor concentrations are not fingerprints, merely reporting the amount of Aroclor that would be present based on the reduced set of PCBs in the sample (Figure 2). Reporting PCBs as Aroclors is insufficient for source apportionment (Erickson, 2017). When conducting an Environmental Forensic Investigation for PCBs it is important to have as much detail about the individual PCBs present as possible. We recommend the use of US EPA method 1668 for PCB fingerprinting as it yields a lower detection limit and is able to quantify all PCB congeners in the samples. This is particularly necessary for investigations involving sediments where PCBs are being altered by microbes or where alternative PCBs sources, such as incidental PCBs, may be present. At Chemistry Matters, we use advanced data analysis tools including receptor modeling, statistical analysis and data visualization to identify potential sources. Our attention to detail and in-depth experience with PCB analysis is crucial for clients facing complex litigious environmental investigations.
Figure 2: Environmental samples no longer resemble Aroclor mixtures. Inexperienced data users may incorrectly assume that an Aroclor designation is related to the source of PCBs. At Chemistry Matters, we know that US EPA Method 8082 is inappropriate for source apportionment. An Aroclor designation from a laboratory does NOT indicate the source of the PCB pollution.
PCBs are commonly measured as part of biomonitoring studies as their lipophilic properties allow them to bioaccumulate and biomagnify in the food chain. The complex nature of Aroclor mixtures and the different behaviors and properties of individual congeners, such as differing toxicities and different degradation rates, exacerbates the complexities of PCB data interpretation, especially in large datasets. The Chemistry Matters team has experience with PCB biomonitoring studies in both an academic and government setting. This includes published research using multivariate statistical analysis of the National Health and Nutrition Examination Survey (NHANES) to evaluate human exposure to PCBs (Megson et al., 2013).
Fate and Transport
The global distribution of PCBs can further complicate the interpretation and use of PCB datasets. Fundamental knowledge about the specific physical and chemical properties of the individual PCB congeners can provide clues to a potential source that might have otherwise gone unnoticed. The amount and position of chlorine on the biphenyl will influence its chemical properties, toxicity, and its environmental fate and transport. Creating a sample plan that adequately characterizes the background concentration of PCBs compared to contaminated samples is required for statistical analysis, source apportionment and potential future litigation cases.
Litigation cases involving communities faced with costly PCB cleanup and potentially responsible parties are complex and often emotionally charged. At Chemistry Matters we focus on scientific facts to help attorneys build their case. Our team has conducted extensive research on the history of analytical chemistry and PCB analysis. We understand the shortcomings of traditional Aroclor analysis and have planned and implemented successful environmental forensic investigations. Our expertise in scientific communication and data visualization can bridge the gap between attorneys, scientists, and a non-technical audience.
ERICKSON, M. D. 2017. Aroclor misidentification in environmental samples: how do we communicate more effectively between the laboratory and the data user? Environ Sci Pollut Res Int.
MEGSON, D., O’SULLIVAN, G., COMBER, S., WORSFOLD, P. J., LOHAN, M. C., EDWARDS, M. R., SHIELDS, W. J., SANDAU, C. D. & PATTERSON, D. G. 2013. Elucidating the structural properties that influence the persistence of PCBs in humans using the National Health and Nutrition Examination Survey (NHANES) dataset. Science of the Total Environment, 461, 99-107.
US EPA. 2019. Learn about Polychlorinated Biphenyls (PCBs) [Online]. Available: https://www.epa.gov/pcbs/learn-about-polychlorinated-biphenyls-pcbs [Accessed].