Admin Core, CEC Core

The Science of PCBs

By cjmattin

A Follow Up to the Science of PCBs Q&A Session (February 26, 2024)

The Superfund Research Program (SRP) is a federal program funded by the National institute of Environmental Health Sciences (NIEHS) of the National Institutes of Health). SRP funds university-based grants to find practical solutions to understand and mitigate health effects associated with hazardous substances through research, training, and community engagement. These activities complement the work of the U.S. Environmental Protection Agency (EPA), the Agency for Toxic Substances and Disease Registry (ATSDR), and other federal and state agencies.  There are currently 24 SRP Centers funded nationally that focus on a range of environmental health priorities. Importantly, a core mission of these Centers is to coordinate and share their expertise to address issues of environmental health concern nationally and globally. 

On February 26, 2024, NC State’s SRP Center (which focuses on per- and polyfluoroalkyl substances, or PFAS) coordinated with our counterparts at the University of Iowa SRP Center (Drs. Keri Hornbuckle and Hans Lehmler) who focus on PCBs, and Dr. Linda Birnbaum, emeritus Director of the NIEHS, to provide an open Q&A Session on the Science of PCBs. We collected all of the questions submitted by the more than 200 attendees during the webinar, including the ones that were answered during the conversation and those which we did not have time to address. Below, we organized the questions into topic areas, and provided responses and links to additional resources. We recognize that some of the responses may not be as concrete as you would like, but making definitive connections between environmental exposures and health outcomes (for example) is complex. We are not able to comment on questions that are specific to university buildings or procedures underway because we don’t have sufficient information to do so at this time. We refer you to the university’s Poe Hall Updates page for information on testing and communications from the university. 

WHAT ARE PCBS? 

Polychlorinated biphenyls (PCBs) are mixtures of up to 209 individual chlorine-containing compounds known as congeners. Not all chlorine-containing chemicals are PCBs. PCBs do not occur naturally and are exclusively manmade.

From 1930 to 1977, Monsanto Corporation was the major U.S. producer of PCBs, which they marketed under the trade name Aroclor. Aroclors are identified by a four-digit numbering code in which the first two digits indicate the type of mixture and the last two digits indicate the approximate chlorine content by weight percent. For example, Aroclor 1242 is a chlorinated biphenyl mixture of PCBs with an average chlorine content of 42%. The manufacture of PCBs was stopped in the U.S. in 1977 because of evidence that they build up in the environment and can cause harmful health effects. PCBs are either oily liquids or solids that are generally colorless. Some PCBs may exist as a gaseous vapor in air. PCBs have no known smell or taste. 

WHY/WHERE ARE THEY LOCATED IN OUR BUILDINGS?

PCBs were used widely as coolants and lubricants in transformers, capacitors, fluorescent lighting fixtures, and other electrical equipment. Monsanto also marketed and sold Aroclors as additives to paint, spray insulation, adhesives, caulking, and sealants, citing the extreme durability of materials with high levels of PCBs.  These uses were widely adopted and used in construction until banned in the 1970s.  

ARE OTHER BUILDINGS SIMILAR IN AGE TO POE HALL POTENTIALLY EMITTING PCBs?

Although PCBs can be emitted from building materials, they can also be contained (e.g., Dr. Hornbuckle mentioned that caulking can be sealed with certain types of tape, which can effectively prevent them from being released into the environment). As stated by Dr. Hornbuckle, many buildings constructed around the same time as Poe Hall used building materials containing PCBs. It is possible that if materials with PCBs were used to construct other NC State buildings, they have since been removed, remediated, or contained; the only way to know if a building has detectable levels of PCBs is to do the appropriate testing. 

ARE PERSONAL ITEMS REMOVED FROM POE HALL BY PRIOR OCCUPANTS AN ONGOING SOURCE OF PCB EXPOSURE?

Because PCBs are lipophilic, meaning that they tend to accumulate in fat or stick to more oily/organic substances, they are unlikely to accumulate or remain on items such as clothing, books, computer surfaces or papers. If you removed items such as those from Poe Hall, you could wipe/wash them, as appropriate to the item, with soap and water as a precaution. Touching a secondary object contaminated with PCBs is not known to be a significant exposure route.

WHAT DOES EXPOSURE MEAN AND WHAT IS CONSIDERED LOW LEVEL?

Exposure is defined as the concentration or the amount of a particular agent that reaches a target organism, system, or (sub)population in a specific frequency for a defined duration (Exposure Scenarios in Toxicology). Exposure to PCBs can occur through multiple routes and sources, including dietary intake, inhalation, dermal contact, and ingestion of dust/soils (Weitekamp et al., 2021).

WHAT ARE THE HEALTH OUTCOMES ASSOCIATED WITH PCBS?

There are many health outcomes associated with exposure to PCBs including cancer, neurological, developmental, liver toxicity and metabolic conditions, among others.

WHAT TYPE OF PROTECTIVE OR REMEDIATION STRATEGIES CAN MITIGATE PCB EXPOSURES?

According to the ATSDR, you should avoid exposures and conditions in your daily life that might further increase your risk of disease or worsen your existing condition. Strategies to reduce your exposure to PCBs can be found HERE. 

Dr. Hornbuckle indicated that typical respiratory masks (e.g., N95s) are generally not protective against PCBs or chemicals in the gas phase. Mitigation and remediation strategies in buildings need to be specific to the location and source of the PCBs. Containment can only be done effectively when the source of the exposure is clear. This requires environmental testing, and typically more testing (larger number of samples from different surfaces and dust) is better to ensure that all potential sources are evaluated

WHAT STUDIES WILL HELP CLARIFY WHETHER THERE ARE CONNECTIONS BETWEEN PCB EXPOSURE AND HEALTH OUTCOMES?

No individual scientific study can answer this question. Instead, scientists use a combination of approaches to determine if there is a connection between an exposure and an adverse health outcome. This process is called risk assessment. Scientists perform experiments using cells, tissues, or animals in the laboratory to determine if an adverse effect following PCB exposure is biologically plausible. In addition, using the tools of environmental epidemiology, they measure PCB exposure and adverse health outcomes in a human population and use mathematical tools (statistics) to determine if higher PCB exposure is associated with an adverse health outcome.  With a lot of data from many people from different study populations, scientists can conduct data analyses in order to make claims about trends in exposure and disease outcomes in a population. Unfortunately, even with a lot of data it is difficult to prove that one person’s exposure to PCBs caused a specific disease. This is because there are many factors that impact whether or not someone who has been exposed to PCBs will experience adverse health effects. Some of these factors include the dose (how much), the duration (how long), and the route of exposure (e.g., inhalation, touch, ingestion). Other important factors include age, sex, diet, genetics, lifestyle, and state of health.

WHAT KINDS OF TESTS OR MEDICAL MONITORING MIGHT BE HELPFUL IF I THINK I HAVE BEEN EXPOSED TO PCBs?

It is always advisable to seek regular medical visits with your doctor, especially if you are noticing symptoms. Many doctors are not trained in environmental health issues or able to make connections between possible exposures, such as to PCBs, and health effects. If your doctor is unfamiliar with PCBs, you can share the resources below with them. There are companies that can test PCBs in blood; however, these results can be challenging to interpret for several reasons. First,  PCBs are detectable in most people.  Second, although one can compare their results to national studies such as the National Health and Nutrition Examination Survey (NHANES), a result that is higher or lower than NHANES does not mean the person has had higher or lower exposure.  Aside from age and sex, which are sorted by NHANES,  metabolism greatly alters the PCB congener signal, as does the timing and duration of exposure, and the particular combination of PCBs to which one is exposed.  Metabolism, timing and specific exposures are highly variable and it is unclear how to interpret a single blood measurement against these factors.  Lastly, the relationship between disease and PCBs in blood is not at all clear.  See this manuscript as an example. 

ADDITIONAL SOURCES