Study finds no link between PCB exposure and cancer mortality

“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 diseases,” said Dr Renate Kimbrough, the study’s principal investigator and a senior medical associate with the IEHR in Washington, DC.

For more than 20 years, the US Government has characterised PCBs as probable human carcinogens, based in part on a 1975 study carried out by Dr Kimbrough of PCBs in rats that were fed large quantities of PCBs in their diets.

The new study is published in the March issue of the peer-reviewed Journal of Occupational and Environmental Medicine, published by the American College of Occupational and Environmental Medicine.

The findings of this study are consistent with those of four other studies of the same population conducted by other researchers over nearly 25 years, but the new study is the largest and most statistically powerful study of humans exposed to PCBs.

The mortality rate focused on the 7,075 men and women who worked between 1946 and 1977 in two Upstate New York General Electric Co. factories which used PCBs in the manufacture of electrical capacitators. The study compared the number and causes of death for the 1,195 members of the study population who died with national and regional averages.

The average follow-up time for the 7,075 workers was 31 years, providing a sufficiently long latency period in which to determine whether there was any increase in cancer mortality.

Some of the workers in the study had PCB levels in their blood as high as several thousand parts per billion (ppb). In the US, the average PCB levels found in the blood of people who have been tested range from 4 to 8 ppb, according to the Agency for Toxic Substances and Disease Registry.

However, no statistically significant increase in deaths due to cancer or any other disease was detected in the workers, including those most highly exposed to PCBs. Nor did the study detect statistically significant increases or decreases in mortality associated with length of employment or latency.

Among the workers, the death rate due to all types of cancer combined was at or significantly below the expected level.

Based on national death rates, 699 and 420 deaths were “expected” among the hourly male and female workers, respectively. Only 586 and 380 deaths, respectively, were observed.

Based on regional death rates, 713 deaths among hourly male workers and 449 deaths among hourly female workers would have been expected. Again, only 586 and 380 deaths, respectively, were observed.

Dr John A. Moore, president of the IEHR, former assistant administrator and acting deputy administrator of the EPA and former deputy director of the National Toxicology Research and Testing Program, NIEHS, National Institutes of Health, 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 the study: “This is a significant study that should be factored into any public discussion of PCBs and human health.”

The new study’s findings are consistent with shorter-term studies of workers in the same factories that were conducted by the National Institute for Occupational Safety and Health, Harvard School of Public Health and the New York State Department of Health, and the Mt. Sinai School of Medicine.