In the largest human study of its kind,
researchers Renate D. Kimbrough, MD, and Martha L. Doemland,PhD, have
found no association between actual human exposure to polychlorinated
biphenyls (PCBs) and death from cancer or any other diseases.
For more than 20 years, the federal government has characterized PCBs
as probable human carcinogens based, in part, on Dr. Kimbroughs
1975 study of PCBs in rats fed a diet containing large quantities of
the substance. 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. Kimbrough, the
studys principal investigator and a senior medical associate
with the Institute for Evaluating Health Risks (IEHR) in Washington, DC.
The findings of the study, published in the March 1999 issue of the
Journal of Occupational and Environmental Medicine, are
consistent with those of four other studies of the same population
conducted by other researchers over a span of nearly 25 years.
However, the current study is the largest and most statistically
powerful one to date.
The study focused on 7,075 men and women who worked between 1946 and
1977 in two upstate New York General Electric factories that used
PCBs in manufacturing electrical capacitors. The study compared the
number (1,195) and causes of death within the study population to
national and regional averages. The average follow-up time for study
members 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 billionwell above the
average PCB levels found in the blood of people in the United States
who have been tested (average PCB levels range from four to eight
parts per billion, according to the Agency for Toxic Substances and
Dr. John A. Moore, president of IEHR, 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.
Smaller Trials Confirm Validity of Current Findings
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. 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 complemented on
the high quality of their study and report as well as the publication
that was prepared from this information.
Dr. Upton chaired a five-member advisory committee established by the
IEHR to review the design, execution, analysis, and interpretation of
This was a well-designed and carefully conducted study,
said Dr. Jack Mandel, an epidemiologist and professor and director of
environmental and occupational health at the University of Minnesota.
The studys 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.
The IEHR conducted the study at the request of and with funding from
General Electric, which operates the businesses where the workers
were employed. General Electric had no role in the conduct of the
study, the evaluation of the data, or the conclusions drawn, said Dr. Kimbrough.