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Research Summary: PCBs

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Robert Herrick, Harvard T.H. Chan School of Public Health

What are PCBs?

Polychlorinated biphenyls (PCBs) are a set of 209 synthetic organic chemicals. They all have a biphenyl ring structure with between one and ten chlorine atoms attached to the ring. PCBs were manufactured in the United States from about 1930 to 1977; the World Health Organization (WHO) estimated in 2003 that approximately 2 × 109 kg (4.4 trillion pounds) of PCBs were produced over those years. PCBs were widely used electrical, heat transfer, and hydraulic equipment; as plasticizers in various products; in paints and finishes; in pigments, dyes, and carbonless copy paper; and in other industrial and commercial applications.7 There are no known natural sources of PCBs.

How are we exposed to PCBs?

PCBs are found in soil, sediment, air, food, and water. They move readily between these environmental media, and they have been detected in polar ice thousands of miles from any place they were manufactured or used. They are remarkably resistant to degradation by natural biological and chemical processes, so they persist in the environment. The ubiquity of PCBs is largely the result of 4 factors: vast amounts of PCBs were produced; PCBs move freely between environmental media (air, water, soil) and the food chain; PCBs naturally degrade very slowly; and PCBs accumulate in living organisms. PCBs are a particular concern in buildings, where they volatilize from building materials and leak from fluorescent light fixtures. PCBs may enter the bodies of people inside buildings through inhalation, ingestion, and dermal absorption (Herrick et al. 2004). Elevated PCB levels in the blood of people in these buildings (including schools) have been reported by many investigators.2,8,11,17,20,30

Sources of PCBs in buildings

A number of products found in buildings contained PCBs.7 These include: dielectric fluid in transformers, capacitors, and other electrical equipment such as switches and circuit breakers; oil in motors and hydraulic systems; microscope oil; capacitors including fluorescent light ballasts; cable insulation; thermal insulation such as fiberglass, felt, foam, and cork; adhesives and tapes; oil-based paints; caulk, window glazing, and other sealants; plastics; ceiling tile coatings; and floor finishes. Some of these materials can still be found in buildings, particularly those constructed or renovated between about 1950 and 1978.

Why are PCBs a health concern?

The Environmental Protection Agency, the WHO, and the United States Department of Health and Human Services have long characterized PCBs as known animal carcinogens and probable human carcinogens. In 2016, however, the International Agency for Research on Cancer (IARC) reassessed the scientific literature and concluded that there is sufficient evidence in humans for the carcinogenicity of PCB. IARC, therefore, upgraded the classification of PCBs to Group 1, known human carcinogens.

While cancer risk has been the primary concern associated with PCB exposure, recent studies have demonstrated a range of other toxic effects, including many that pose particular hazards in built environments such as schools.21

  • Asthma & Respiratory Effects. Adults and children have an increased risk of asthma and infectious respiratory diseases when exposed to PCBs.4,18 There is a relationship between PCB exposures and lowered levels of immunoglobulins M and A (IgM and IgA) and increases in respiratory infections.22
  • Attentional Deficits and Cognitive Function. Adults who work in buildings with PCB window caulk showed higher rates of attentional deficits.26 Low-level prenatal exposure to PCBs caused an increase in ADHD-like behaviors in children.28 Children who had prenatal exposure to PCBs had higher incidence of behavioral disorders and lower IQ scores when they were 9 years old.32 Adolescents with elevated serum PCBs did more poorly on several tests of cognitive function than adolescents with low PCBs.23
  • Endocrine Effects. Adolescent girls with high PCB levels reach puberty at a younger age than girls with lower PCBs.6 In adolescents, thyroid function is reduced if their serum PCB level is elevated.29 Higher PCB levels in men is associated with a reduction in the levels of the male sex hormone, testosterone.10
  • Immune System Effects. PCBs are associated with immune system disruptions including increases in B cells and decreases in CD8+ and natural killer cells.34 Babies with higher prenatal PCB exposures had reduced immune response after vaccination for measles, mumps and rubella.35 Reduced antibodies against diphtheria and tetanus later in childhood were associated with higher PCB exposure in toddlerhood.3 PCB exposure altered lymphocyte distributions, decreased wheeze, and increased otitis media.36
  • Prenatal & Infant Exposure. Low level prenatal exposure to PCBs may affect thyroid hormone homeostasis.5 Prenatal exposure to PCBs may affect growth, especially in girls.16 Growth deficits were also seen among infants born near a chemical manufacturing plant that produced PCBs,14 specifically lower thymic index, which is an estimate of the volume of the thymus, an organ that plays a role in the differentiation and maturation of t-lymphocytes (Tcells, a critical part of the immune system).25 Associations were reported between prenatal PCB and p,p-DDE exposures and poor attention in early infancy, including alertness, quality of alert responsiveness, and cost of attention.27
  • Diabetes & Heart Disease. Hospitalization rates for diabetes in communities near a toxic waste site containing PCBs were amplified.15 Residents living in communities adjacent to the Hudson River, which contains high levels of PCBs, had an increased rate of hospitalization for coronary heart disease by over 35% and for acute myocardial infarction by nearly 40%.31 High levels of PCBs cause the liver to make more cholesterol and lipids, which then increase the risk of cardiovascular disease.9

What can I do?

The issue of PCBs in buildings requires attention. There is unequivocal evidence that PCBs are common in building materials, and fluorescent light ballasts. These sources can cause PCB contamination of the building environment. Airborne PCB levels far in excess of EPA health-based guidelines have been frequently measured in buildings. People occupying these buildings, including students, teachers and staff of schools, residents, or workers in contaminated buildings have been shown to have elevated serum PCB levels.

What is also clear is the lack of policies and guidelines for owners and occupants of buildings that may contain PCBs. A 2016 report by US Senator Markey24 concluded that in the case of schools, there is a lack of transparency and inconsistency in communication between schools, EPA, the states, and the people in the school buildings. In addition, the Senate report found that EPA enforcement and communications are inconsistent. For example there is no requirement for a building owner or property manager to conduct sampling to determine whether PCBs are present in a building. Under TSCA regulations, however, if PCBs are found at levels exceeding 50 ppm that is considered an unauthorized use. Some EPA regions have interpreted that to mean that the PCB-containing materials must be removed,33 while other regions have advised school districts not to test for PCBs.24 Given the uncertainties surrounding the associations between PCB exposures and health effects, particularly among children, precautionary approaches to managing PCBs in building materials are warranted. Effective mitigation approaches are available and have been demonstrated to effectively minimize exposure.1,19


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