PCBs (polychlorinated biphenyls) are in the news again, with the Environmental Protection Agency (EPA) planning to mandate the expenditure of hundreds of millions of dollars dredging the Hudson River in New York and the Fox River in Wisconsin to remove PCBs from river sediment.
We have been told for years that PCBs are dangerous, whenever humans have worked with them or have otherwise been exposed to them. Yet the best available research on the subject fails to back up this claim.
The largest-ever human study of the effects of occupational exposure to PCBs, conducted by researchers Renate D. Kimbrough, MD and Martha L. Doemland, PhD, found no association between human exposure to PCBs and deaths from cancer and any other disease.
“This new study provides strong evidence that even long-term human exposure to PCBs, at higher levels than are found in the environment, is not related to an increase in deaths from cancer or any other disease,” said Kimbrough, the study’s principal investigator and a senior medical associate with the nonprofit Institute for Evaluating Health Risks in Washington, DC.
For more than 20 years, the federal government has characterized PCBs as probable human carcinogens, based in part on Kimbrough’s first 1975 study of rats fed large quantities of PCBs.
Kimbrough’s latest study was published nearly 25 years later, in the March 1999 issue of the peer-reviewed Journal of Occupational and Environmental Medicine, published by the American College of Occupational and Environmental Medicine. She collected and evaluated health data on more than 7,000 men and women who worked between 1946 and 1977 for General Electric in two upstate New York factories that used PCBs in the manufacture of electrical capacitors. PCBs were widely used in electric transformers for years, contained in an oily liquid that withstands intense heat and is not flammable.
Kimbrough’s study also compared national and regional mortality rates of populations not exposed to PCBs with those who were exposed, and describes the numbers and causes of death for the 1,195 members of the exposed study population who died during this time period.
According to Kimbrough, some of the GE employees in her study had PCB levels in their blood as high as several thousand parts per billion. In the United States, the average PCB levels found in the blood of people who have been tested range from 4 to 8 parts per billion, according to the Agency for Toxic Substances and Disease Registry.
Dr. John A. Moore, acting deputy administrator of EPA and former deputy director of the National Toxicology Research and Testing Program of the National Institutes of Health, was asked to comment on Kimbrough’s study. He said, “The findings of this study are consistent with a belief that cancer risks from exposure to PCBs have been overstated. The newer laboratory data of the past several years support such a view and also prompted the EPA to reduce the factors they use to estimate PCB cancer risks.”
Dr. Arthur C. Upton, former director of the National Cancer Institute and currently a professor at the Robert Wood Johnson Medical School, said of Kimbrough’s work, “This is a significant study that should be factored into any public discussion of PCBs and human health. Dr. Kimbrough and her colleagues were meticulous in their efforts to gather and verify information on the 7,075 individuals who were part of the investigation. The analysis of the data and conclusions are scientifically appropriate and the authors are to be complimented on the high quality of their study and report, as well as the publication that was prepared from this information.
Members of the peer panel who reviewed the study before its publication commended Kimbrough and Doemland’s determination to examine the records of each of the more than 7,000 people who had worked in the electrical equipment factories for at least 90 days over a 30-year period, noting they had even found 738 workers not included in previous studies.
The new study’s findings are consistent with shorter-term studies of workers in the same factories, conducted by the National Institute for Occupational Safety and Health, Harvard School of Public Health, the New York State Department of Health, and the Mt. Sinai School of Medicine.
Hiram M. Perry is a retired agricultural journalist who has written extensively on agricultural practices and the environment for 50 years. He can be reached by email at [email protected].