Health Effects of PCBs

PCBs have been demonstrated to cause a number of serious health effects in animals, including:

EPA’s Integrated Risk Information System Program identifies and characterizes the health hazards of chemicals found in the environment via individual assessments. Each IRIS assessment can cover a chemical, a group of related chemicals, or a complex mixture. IRIS studies in humans also support evidence for potential carcinogenic and non-carcinogenic effects of PCBs. You can find the IRIS primary assessment on PCBs on the IRIS website. The different health effects of PCBs may be interrelated. Alterations in one system of the body may have significant implications for the others. The potential health effects of PCB exposure are discussed in greater detail below.

Cancer

PCBs are one of the most widely studied environmental contaminants. Many studies in animals and human populations have been performed to assess the potential carcinogenicity of PCBs. EPA's first assessment of PCB carcinogenicity was completed in 1987. At that time, data was limited to Aroclor 1260.

In 1996, EPA completed a reassessment of PCB carcinogenicity following a directive from Congress. The reassessment, titled PCBs: Cancer Dose-Response Assessment and Application to Environmental Mixtures (pdf)(149 KB) reflected the Agency's commitment to the use of the best science in evaluating health effects of PCBs. The reassessment was peer reviewed by 15 experts on PCBs, including scientists from government, academia, and industry. The peer reviewers agreed with EPA's conclusion that PCBs are probable human carcinogens.

The cancer reassessment determined that PCBs are probable human carcinogens, based on the following information:

  • EPA reviewed all of the available literature on the carcinogenicity of PCBs in animals as an important first step in the cancer reassessment, which presented clear evidence that PCBs cause cancer in animals.
  • An industry scientist commented that "all significant studies have been reviewed and are fairly represented in the document".
  • An industry-sponsored peer-reviewed rat study, characterized as the "gold standard study" by one peer reviewer, demonstrated that every commercial PCB mixture tested caused cancer.
  • A number of epidemiological studies of workers exposed to PCBs have been performed that raise concerns for the potential carcinogenicity of PCBs. These studies of PCB workers found increases in rare liver cancers and malignant melanoma.
  • The presence of cancer in the same target organ (liver) following exposures to PCBs both in animals and in humans and the finding of liver cancers and malignant melanomas across multiple human studies adds weight to the conclusion that PCBs are probable human carcinogens.
  • The newer studies reviewed in the PCB reassessment allowed EPA to develop more accurate potency estimates than previously available for PCBs.
  • The reassessment provided EPA with sufficient information to develop a range of potency estimates for different PCB mixtures, based on the incidence of liver cancer and in consideration of the mobility of PCBs in the environment.
  • The reassessment resulted in a slightly decreased cancer potency estimate for Aroclor 1260 relative to the 1987 estimate due to the use of additional dose-response information for PCB mixtures and refinements in risk assessment techniques (e.g., use of a different animal-to-human scaling factor for dose).
  • The reassessment also concluded that the types of PCBs likely to be bioaccumulated in fish and bound to sediments are the most carcinogenic PCB mixtures.

EPA is not alone in its conclusions regarding PCBs and cancer. In 2015, the International Agency for Research on Cancer determined that PCBs are carcinogenic to humans. This conclusion was supported by newer studies in humans, published after EPA finished its reassessment, which provided more evidence that PCBs can lead to cancer, particularly malignant melanoma. Similarly, the National Toxicology Program has also stated that it is reasonable to conclude that PCBs are carcinogenic in humans. Additionally, the National Institute for Occupational Safety and Health has determined that PCBs are a potential occupational carcinogen.

Some of the studies in humans have not demonstrated an association between exposures to PCBs and disease. It is important to note that epidemiological studies share common methodological limitations to their ability to detect important health effects (or define them as statistically significant) even when they are present. These limitations include having too few individuals in a study for an effect to be revealed, difficulties in determining actual exposure levels, or confounding factors that often co-occur with PCB exposure, including smoking, drinking alcohol, and exposure to other chemicals in the workplace. Additionally, epidemiological studies may not be able to detect increases in cancer over background levels unless either the cancer rate following contaminant exposure is very high, or the PCB exposure produces a very unusual type of cancer. Studies that do not demonstrate an association between exposure to PCBs and disease are most appropriately viewed as inconclusive, and do not mean that PCBs are safe.

It is very important to note that the composition of PCB mixtures changes following their release into the environment. Because the types of PCBs that tend to bioaccumulate in fish and other animals and bind to sediments happen to be the most carcinogenic components of PCB mixtures, people who ingest PCB-contaminated fish or other animal products and contact PCB-contaminated sediment may be exposed to PCB mixtures that are even more toxic than the PCB mixtures contacted by workers and released into the environment.

Non-Cancer Effects

EPA evaluates all of the available data in determining the potential noncarcinogenic toxicity of environmental contaminants, including PCBs. Based on extensive studies conducted using environmentally relevant doses, EPA found clear evidence that PCBs have significant toxic effects in animals, including non-human primates. PCBs can affect an animal’s immune system, reproductive system, nervous system and endocrine system. The body's regulation of all these systems is complex and interrelated. As a result, it is not surprising that PCBs can exert a multitude of serious adverse health effects.

The 2023 EPA report, A Systematic Evidence Map of Noncancer Health Endpoints and Exposures to Polychlorinated Biphenyl Mixtures (pdf)(7.9 MB), and supporting data provides a comprehensive review of human and other mammalian studies of noncancer health endpoints measured with exposure to PCBs. The review identified 953 studies in humans and 637 in other mammals.

Immune Effects

The immune system is critical for fighting infections, and diseases of the immune system have very serious potential implications for the health of humans and animals. For example, individuals with diseases of the immune system may be more susceptible to pneumonia and viral infections. The immune effects of PCB exposure have been studied in Rhesus monkeys and other animals. It is important to note that the immune systems of Rhesus monkeys and humans are very similar. Studies in monkeys and other animals have revealed a number of serious effects on the immune system following exposures to PCBs:

  • Significant decrease in size of the thymus gland, which is critical to the immune system in infant monkeys.
  • Reductions in the response of the immune system following a challenge with sheep red blood cells. This is a standard laboratory test that determines the ability of an animal to mount a primary antibody response and develop protective immunity.
  • Decreased resistance to Epstein-Barr virus and other infections in PCB-exposed animals.

These animal studies were not able to identify a level of PCB exposure that did not cause effects on the immune system.

Studies in humans have found that individuals infected with Epstein-Barr virus had a greater association of increased exposures to PCBs. It also increased the risk of non-Hodgkin's lymphoma more than for those who had no Epstein-Barr infection. These findings are consistent with increases in infection with Epstein Barr virus in animals exposed to PCBs.

Since PCBs suppress the immune system and immune system suppression has been demonstrated as a risk factor for non-Hodgkin's lymphoma, suppression of the immune system is a possible mechanism for PCB-induced cancer. Immune effects were also noted in humans who experienced exposure to rice oil contaminated with PCBs, dibenzofurans, and dioxins.

Taken together, the studies in animals and humans suggest that PCBs may have serious potential effects on the immune systems of exposed individuals.

Reproductive and Developmental Effects

Reproductive and developmental effects of PCBs have been studied in a variety of animal species, including Rhesus monkeys, rats, mice and mink. Potentially serious effects were seen in monkeys and a number of other animal species following exposures to PCB mixtures. Most significantly, PCB exposures were found to reduce the birth weight, conception rates and live birth rates of monkeys and other species; and PCB exposure reduced sperm counts in rats. Effects in monkeys were long lasting and were observed long after the dosing with PCBs occurred.

Studies of reproductive and developmental effects have also been carried out in human populations exposed to PCBs. Children born to women who worked with PCBs in factories showed decreased birth weight and a significant decrease in gestational age with increasing exposures to PCBs. Studies in fishing populations believed to have high exposures to PCBs also suggest similar decreases. This same effect was seen in multiple species of animals exposed to PCBs and suggests that reproductive and developmental effects may be important in humans following exposures to PCBs.

Neurological Effects

Proper development of the nervous system is critical for early learning and can have potentially significant implications for the health of individuals throughout their lives. Effects of PCBs on nervous system development have been studied in monkeys and a variety of other animal species. Newborn monkeys exposed to PCBs showed persistent and significant deficits in neurological development, including visual recognition, short-term memory and learning. Some of these studies were conducted using the types of PCBs most commonly found in human breast milk.

Studies in humans have suggested effects similar to those observed in monkeys exposed to PCBs, including learning deficits and changes in activity associated with exposures to PCBs. The similarity in effects observed in humans and animals provide additional support for the potential neurobehavioral effects of PCBs.

Endocrine Effects

There has been significant discussion and research on the effects of environmental contaminants on the endocrine system ("endocrine disruption"). While the significance of endocrine disruption as a widespread issue in humans is a subject of ongoing study, PCBs have been demonstrated to exert effects on thyroid hormone levels in humans and animals. Thyroid hormone levels are critical for normal growth and development, and alterations in thyroid hormone levels may have significant health implications.

It has been shown that PCBs decrease thyroid hormone levels in rodents, resulting in developmental deficits including deficits in hearing. Studies in humans, including infants and children, also suggest a link between PCB exposure and changes in thyroid hormone levels. Different studies have found either increases or decreases in hormone levels, depending on how PCB exposure was measured, the age of the group being studied, and the details of the exposure scenario. While hormone levels often remained within normal ranges, noticeable differences were reported between those exposed to PCBs and those who were not. Additional research would be useful to better understand the significance of these effects on human health and to clarify the potential risks associated with PCB exposure.

Other Non-cancer Effects

A variety of other non-cancer effects of PCBs have been reported, including the following:

  • Dermal and ocular effects in monkeys and humans.
  • Liver toxicity in rodents.
  • Elevated blood pressure, serum triglyceride, and serum cholesterol in humans.

Polychlorinated Biphenyls (PCBs)

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Last updated on April 14, 2026