National Drinking Water Database

Polychlorinated biphenyls (PCBs)

Polychlorinated biphenyls (PCBs) are toxic, persistent, bioaccumulative, and lipophilic ("fat-loving") chemicals that were used widely as coolants and lubricants in transformers, capacitors and other electrical equipment (Agency for Toxic Substances and Disease Registry (ATSDR) 2000b). The manufacture of PCBs was banned in the United States in 1977 because of concern for human health impacts, but PCBs are still widely detected in the general population. Polychlorinated biphenyls build up and are stored in fatty tissues and fluids, such as breast milk, and can be passed on to fetuses and infants during pregnancy and lactation.

Even though PCBs have been banned for manufacture in the U.S. for over 30 years, they are still released into the environment. A total of 2,504,776 pounds were reported as released by U.S. industries in 2001, over 99 percent of which was land-filled as part of hazardous waste clean-up (U.S. Environmental Protection Agency (USEPA) 2009i).

There is broad agreement from multiple government agencies that PCBs are likely to cause cancer in people (Agency for Toxic Substances and Disease Registry (ATSDR) 2000b). While agencies use different labels to describe the human cancer risk, ranging from "probable" or "probably," to "reasonably anticipated," the message is the same - PCBs are expected to cause cancer in people.

In recently published human studies, PCBs have been associated with an elevated risk of breast cancer (Brody 2007) and prostate cancer (Prins 2008), possibly due to their effects on the hormonal system and interference with estrogen signaling (Wolff 2008).

Strong evidence for PCB carcinogenicity has been observed in studies of laboratory animals. Scientists from General Electric published a study in 1998 showing that all four commercial PCB mixtures tested, called Aroclors, caused cancer in rats (Mayes 1998). Each commercial mixture was shown to cause liver tumors in females and thyroid tumors in male rats. Other studies have also shown that PCBs cause liver tumors (USEPA 1996a). One study, conducted by the National Cancer Institute (NCI) in 1978, found that a commercial PCB mixture caused a statistically significant increase in the incidence of gastric adenocarcinoma, a rare type of stomach tumor (Integrated Risk Information System (IRIS) 1997b).

A growing number of major epidemiology studies consistently find that infants and children with higher PCB exposures during development score lower on numerous measures of neurological function, ranging from decreased IQ scores to reduced hearing sensitivity (Schantz 2003; Sagiv 2008; Stewart 2008).

Some of these effects have been noted at low levels of PCB exposure. A study of Michigan children found that PCBs at 9.7 ng/ml (parts per billion or ppb) in maternal serum during fetal development can cause adverse brain development, and attention and IQ deficits that appear to be permanent (Jacobson and Jacobson 1996). Notably, it was the maternal PCB levels, and not the PCB levels in children at 4 and 11 years of age (by which time child PCB levels had decreased substantially), that was associated with IQ deficit, underscoring the importance of in utero exposures from a mother's consumption of PCB-contaminated fish. These findings in human epidemiological studies are in agreement with PCB neurotoxicity in laboratory animals (Yang 2009).

PCBs are also associated with adverse developmental effects. For example, one study reported that male babies were more likely to have low birth weight if their mothers lived in zip codes that contain, or are next to, a PCB-contaminated hazardous waste site (Baibergenova 2003). A similar effect was noted for female babies, but the effect was not as strong and did not reach statistical significance.

PCBs have long been known to damage the immune system in laboratory animals (Hertz-Picciotto 2008). In fact, the studies conducted to date have not been able to find a PCB dose that does not impact the immune system (USEPA 1996a). These animal studies show that PCBs can alter the size of important immune organs, impair the development of immunity and increase vulnerability to infections.