STATS at George Mason University

Do pcbs cause cancer in humans?

Of course, the premise behind the EPA guidelines is that there really is a quantifiable risk of developing cancer from consuming trace levels of PCBs in salmon (as well as beef and dairy products, which also contain minute traces of PCBs).

The EPA believes that PCBs are probable human carcinogens based on occupational studies of workers exposed on a daily basis over many years to high levels of PCBs in industrial settings and, more significantly, on studies showing that chronic exposure to high doses of PCBs produce tumors in rats. (“PCBs Cancer Dose-Response Assessment and Application to Environmental Mixtures,” National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency, 1996).

The problem with the EPA’s case against PCBs is that scientific research has yet to prove that prolonged exposure to high levels of PCBs in industrial settings causes cancer, let alone that exposure to much lower levels of PCBs in the environment is equally deleterious.

This is not to say that scientific inquiry has conclusively proved that PCBs cannot cause cancer in humans; the occupational studies on workers who came into direct contact with PCBs in industrial settings are limited in scope and sample size. Nevertheless, the largest of these studies, conducted by the National Institute for Occupational Safety and Health (NIOSH), found that the rate of cancer among such workers was slightly lower than that of the general population, and that there was no statistically significant increase in the rates for individual types of cancers (Brown and Jones 1981).

We are unfortunate enough to also have two cases where PCB mixtures were accidentally ingested. The first involved 1,665 people in Western Japan in the late 1960s who consumed rice bran oil contaminated with PCB mixtures at 2000 to 3000 parts per million. Immediate effects included chronic acne, nausea, fatigue and several incidences of liver disorders. During the next 11 years, 51 people died, one-third from cancer.In a similar unexposed group, only one-fifth would have been expected to die of cancer.

In 1978 in Taiwan, there was another incident of rice bran oil contamination that resulted in elevated levels of liver disease. And children of those poisoned in both groups showed a variety of developmental abnormalities. Yet subsequent research has concluded that the toxicity of the oil was not directly attributable to PCBs, but rather to a complex series of chemicals produced when the PCBs degraded after the oil was heated.

Given such evidence, the American Council for Science and Health (ACSH) has concluded that, “There is no credible evidence that PCB exposure in the general environment, in fish, or even very high levels in the workplace, has ever led to an increase in cancer risk.” Although the ACSH has drawn flak from environmentalists and other activists for accepting money from industry and corporate sources, their 1997 analysis of the risk from PCBs — “Public Health Concerns about Environmental Polychlorinated Biphenyls” — was published in the peer-reviewed journal, “Ecotoxicology and Environmental Safety.”

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