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Current information is available through the
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A PUBLICATION OF THE
Hanford Health
Information Network |
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Introduction
This publication discusses the question of whether there is an increased risk for
developing cancer among people
who were exposed to radiation released from Hanford. It offers the opinions of three
scientists: Drs. Ernest J. Sternglass, Alice M. Stewart and Gregg S.
Wilkinson. Their essays follow in alphabetical order.
Many people who have called the Hanford Health Information Lines have asked
about the relationship between cancer and the exposure to radioactive materials
released from Hanford. The chance of a person getting cancer from exposure to a
hazardous or radioactive substance is called a risk estimate. Even though the relationship
between cancer and radiation exposure is an estimate, any exposure to radiation carries
with it some risk of producing harm.
Hanford-specific health risk estimates will not be possible until health studies of
people exposed to Hanford's radioactive releases are completed. However, the Network
asked scientific experts to offer their opinions as to the likely risks posed to humans from
the Hanford releases.
To better understand the following essays, here are the questions the
Network asked each of the scientists:
In your opinion, what kind of dose range from Hanford could have
posed a public health risk by causing cancer?
Comment specifically on the various nuclides for which doses will be
calculated by the Hanford Environmental Dose Reconstruction Project.
How would you show that this dose range was responsible for cancer? What
evidence could be used?
What do you mean by a public health risk?
Are there other issues you consider important to understanding the relationship between Hanford and the risk
of cancer?
The Network gave each contributor the current estimates of the annual releases
of 11 radionuclides released from Hanford. (Please refer to HHIN's The Release of Radioactive Material from Hanford:
1944-1972.) These are the radioactive materials for which the Hanford
Environmental Dose Reconstruction project is calculating doses.
The Hanford Environmental Dose Reconstruction (HEDR) Project was
established to estimate what radiation dose people living near Hanford some time
between 1944 and 1992 might have received from releases of radioactive materials. The
Technical Steering Panel, which directed the study, completed its role in 1995. The
federal Centers for Disease Control and Prevention (CDC) is now working with the HEDR
Task Completion Working Group to continue public participation and to assure
completion of the remaining HEDR activities. When using information from the Dose
Reconstruction Project and other studies, readers should keep in mind that research
results depend on a number of factors, such as the information available, and the
methods and type of analysis used.
The Network asked each scientist to write for the general public. Network staff
edited each piece to make it as easy to understand as possible without losing the
necessary scientific details.
Each scientist has approved the edited version of their essay and selected
references follow each piece. A complete bibliography of all the references used by the
three scientists is available from the Network.
ERNEST J. STERNGLASS, Ph.D. has been Professor
Emeritus of Radiology at the University of Pittsburgh's School of Medicine since 1983. He
has held professorships in radiology and physics at several universities, including
Stanford, Indiana University, and the Institute Henri Poincare in Paris, France. Dr.
Sternglass was the Director of the Apollo Lunar Scientific Station Program while at
Westinghouse Research Laboratories. His doctorate in Engineering Physics (1953)
comes from Cornell University, as does his post-graduate and undergraduate degrees in
Engineering Physics and Electrical Engineering, respectively. He taught physics at
George Washington University and held a research fellowship at Cornell University. Dr.
Sternglass has received many academic and professional honors, is a member of several
professional societies and holds 13 patents. He is the author of several books on
low-level radiation.
Radiation Relatively More
Harmful at Low Levels
Constant, low levels of radiation are relatively more harmful than higher levels of
exposure over a short time.
Exposure to radioactive substances, such as those released from Hanford,
increases the risk of cancer. There
is increasing evidence that the risk of cancer is proportionately greater at low doses. These low doses are only a
thousandth of the dose levels of the Japanese atomic bomb survivors. The atomic bombs
exposed the Japanese to short bursts of
external radiation.
Internal radiation doses from contaminated food and water over a long time
appear to damage the body much more than the same doses from short external
exposures, such as X-rays. Around
Hanford, people received internal exposure over a long time.
Highly toxic forms of oxygen, called free radicals, can increase the harmfulness
of radiation exposure. The power of free radicals to do harm increases as the dose levels
decrease. The lower the dose per year, the higher the risk. The increasing harmfulness of
free radicals has been found down to levels of 20-200 millirem per year. This level of exposure is equal
to the amount received from background radiation.
The interactions between the damage to different organs from various
radioactive substances are very complex. A dose estimate to a given organ is not enough
information to estimate possible damage to the body. Whether internal exposure will
result in a cancer that spreads to other parts of the body depends on the ability of the
immune system to detect and destroy the cancer cells. The immune system fights
diseases in the body.
Strontium-90 is one of the substances
released from Hanford. Strontium-90 irradiates the bone marrow where cells of the
immune system originate. Eating food contaminated with strontium-90 affects the ability of
the immune system to detect and destroy cancer cells.
To measure the public health risk from Hanford's radiation releases, it is
necessary to look at cancer death rates over time. The change in cancer death rates since
the early 1950s in the area downwind from Hanford should be compared with the change
in cancer death rates in the areas upwind.
Joseph J. Mangano did such a comparison for the area around the Oak Ridge
National Laboratory in Tennessee (Mangano 1994). In the 94 counties around Oak
Ridge, the age-adjusted cancer death rate rose 34.1% between 1950-52 and 1987-89. It
rose 5.1% for the United States as a whole during that time. In the nearby counties exactly
downwind of Oak Ridge, the cancer death rate rose 50.8% while it rose only 7.1% upwind
of the facility.
These findings strongly support the idea that airborne releases were the cause
of some deaths from cancer and agree with another study recently published (Gould
1994). This second study showed that even smaller airborne releases from commercial
nuclear power plants in nine regions of the United States correlated closely to breast
cancer death rates.
This evidence shows that constant, low levels of radiation are relatively more
harmful than higher levels of exposure over a short time. This is especially important for
people who were exposed to the radiation releases from Hanford.
Selected References Gould,
J.M., E.J. Sternglass, "Nuclear Fallout, Low Birthweight, and Immune Deficiency."
International Journal of Health Services: 1994; 24 (2): 311-335.
Mangano, J.J. "Cancer Mortality Near Oak Ridge, Tennessee." International
Journal of Health Services: 1994; 24 (3).
ALICE M. STEWART, M.D., has been a Senior Research
Fellow at Birmingham University in England since 1974, where her work continues on the
Oxford Survey of Childhood Cancers. This study began over 30 years ago while she was
pursuing her career in scientific research in social medicine at Oxford University. Her epidemiological findings while at
Oxford linked the use of pre-natal X-rays to childhood leukemias. She continues to speak
out against the risks of low-dose radiation exposure to workers in the nuclear industry. Dr.
Stewart was a founding member of both the International Epidemiological Society and
the Society for Medicine. She received her medical degree from Cambridge University in
1932 and was the youngest woman to be elected to the British Royal College of
Physicians before 1947. She continues to study the health of workers in U.S. nuclear
weapons facilities.
Total Risk of Radiation
Exposure Underestimated
Influence of Weakened Immune System Missed
Exposure to radiation can
harm the immune system. A weakened immune system can result in an exposed person
catching an infection and possibly dying from it or any infection-related cause of death.
Such a person might also have developed a cancer from the radiation exposure. But
because the person died from another illness first, the cancer did not have time to fully
develop and be diagnosed. By not accounting for deaths from weakened immune
systems, current risks of cancer deaths from radiation exposure underestimate the
harmfulness of radiation.
The present method used to estimate effects of radiation grossly underestimates
the cancer risk from low-dose exposure. Evidence for this comes from studies of
Japanese A-bomb survivors, British children and American nuclear workers. The
Japanese A-bomb survivor study misrepresents the cancer risks because it fails to take
into account those people who died before 1950. It wasn't until 1950 that U.S. scientists
began the A-bomb survivor study.
It is unlikely that the harmfulness of radiation is reduced at low-dose levels.
Rather, it is possible that the mutations to cells caused by
repeated and unavoidable exposures to
background radiation are the most common cause of cancer.
In addition, a large British study of childhood cancer deaths (Oxford Survey of Childhood
Cancers) has found many reasons why detection of cancers caused by constant low-level
radiation is always a complex problem.
According to data from the Oxford Survey, childhood cancers include a relatively
large number of embryomas, cancers of the embryo. These may be the result of exposure
while in the womb to background radiation, as well as medical X-rays. Furthermore, for all
cancers that began in the womb, there was evidence of mounting sensitivity to infections
while the cancers were growing. Consequently, deaths during the latency period (the time
it takes for cancers to develop) of a childhood cancer are common. The latency period
deaths also result in falsely low rates of leukemia and lymphoma for children
who have survived high rates of infant mortality. Leukemia and lymphoma are cancers of
white blood cells.
Besides causing early cancer deaths, infections can also shorten the latency period. In countries
with low rates of infant mortality, cases of leukemia and lymphoma are relatively common.
However, these cases are distributed unevenly: there are higher rates in rural areas and
in people who are well-to-do.
According to the Oxford Survey, immunizations against infectious diseases have
reduced the risk of an early cancer death. However, African children who live in areas of
holoendemic
malaria and have survived a high risk of dying during infancy rarely develop
leukemia. Therefore, it is possible that, even in children, the spread of cancer cells can be
prevented by immune system reactions to the dangerous situations created by the
malarial parasite. Based on this evidence, the number of cancers depends less upon the
level of exposure to background radiation than upon the nature and intensity of
indigenous infections. In addition, the number of cancers depends on such things as
levels of family income, population density and the availability of immunizations.
The only measurable effect of the Hanford releases could be the one caused by
the releases of iodine-131. By its effect on the thyroid gland, these releases would
increase the risk of cancers that are normally rare. Thyroid cancers accounted for only
three of the 22,351 cancers eventually included in the Oxford Survey. Therefore, even a
single case of thyroid cancer among persons exposed (in the womb or as young children)
to the iodine releases from Hanford would be a highly suspicious finding.
Evidence of a special association between radioactive iodine and thyroid
cancers has already been obtained from Marshall
Islanders and Ukrainian children.
Therefore, I recommend that a study identify all live births for the period of 1944-1955 in
the regions covered by the Hanford
Environmental Dose Reconstruction Project, as well as all cancer deaths in this
population. This relatively simple procedure would detect any thyroid cancer effect of the
reconstructed doses. Remember, even one case of thyroid cancer would be highly
suspicious. Comparing the thyroid cancer effect to other populations and other cancers
could be done to estimate the overall effect of all the Hanford releases.
Selected References
Bithell, J.F., A.M. Stewart, "Pre-Natal Irradiation and Childhood Malignancy: A Review
of British Data from the Oxford Survey." British Journal of Cancer: 1975; 31:
271-287.
Gilman, E.A., G.W. Kneale, E.G. Knox, A.M. Stewart, "Pregnancy X-rays and
Childhood Cancers: Effects of Exposure Age and Radiation Dose." Journal of the
Society for Radiological Protection: 1988; 8 (1): 3-8.
Kneale, G.W., A.M. Stewart, L.M. Kinnier Wilson, "Immunizations Against Infectious
Diseases and Childhood Cancers." Cancer Immunology and Immunotherapy:
1986; 21: 129-132.
Stewart, A.M., G.W. Kneale, "The Immune System and Cancers of Fetal Origin."
Cancer Immunology and Immunotherapy: 1982; 14: 110-116.
Stewart, A.M., J. Webb, D. Giles, D. Hewitt, "Malignant Diseases in Childhood and
Diagnostic Irradiation In Utero." The Lancet: 1956; ii: 447.
Gregg S.
Wilkinson, M.A., Ph.D. is a Professor of Epidemiology in the
Department of Preventive Medicine and Community Health, and Director of the Division of
Epidemiology and Biostatistics at the University of Texas Medical Branch (UTMB) in
Galveston, Texas. Prior to joining the faculty at UTMB, Dr. Wilkinson was an Associate
Epidemiologist with Epidemiology Resources, Inc., and he also served as the Principal
Investigator for the nationwide study of U.S. plutonium workers at the Los Alamos
National Laboratory. He received his doctorate in 1973 from the State University of New
York at Buffalo and held a post-doctoral fellowship at Duke University Medical Center. In
addition to his research concerning low- dose effects from ionizing radiation, Dr.
Wilkinson's research interests include the epidemiology of neural tube and other birth
defects, environmental and occupational epidemiology and epidemiological methods.
Hanford's Radiation and the Risk of
Cancer
At what levels of exposure to radioactive
materials is there an increased risk of cancer? Two factors must be known
before that question can be answered. First, information on exposures (or doses) to individual members of the
population under consideration must be calculated. Second, health problems that the
population experienced after the exposure must be identified. From this information, a risk
estimate can be made.
Risk estimates are based on statistical calculations. For mathematical
reasons, risk estimates are more supportable if there has been a large number of people
exposed and their range of doses is large.
We still lack sufficient information to assess the risk to people exposed to the
Hanford radiation releases because there is no comprehensive information on the health
of those exposed. Additionally, dose estimates for specific individuals are not yet
available.
Regarding the list of radioactive materials for which doses are being calculated, I
am limiting my comments to the radioactive elements with which I have some experience:
plutonium-239 and iodine-131.
Plutonium-239
Plutonium-239 has a very long half
life of more than 24,000 years. Because of this, there is a concern that releases to the
environment will be cumulative and, for all practical purposes, permanent. However,
plutonium must be inhaled, ingested or injected (through contamination in wounds)
before it can cause biological damage.
Plutonium causes cancer in animals. One human study suggested that Rocky
Flats workers who had plutonium uptakes of more than two nanocuries had increased risks of
dying (Wilkinson 1987). A similar study of Hanford workers, however, found no increased
risks (Gilbert 1989). Unfortunately, the Hanford study had little chance of detecting
anything other than huge increases in risk. This was due to the relatively small number of
exposed workers and the skewed nature of the exposures. There were few workers with
recorded body burdens
greater than 5% of the maximum permissible body burden (2 nanocuries). The U.S.
Department of Energy sets the standard for the maximum permissible body burden at 40
nanocuries of plutonium.
Generally, workers experience higher exposures to plutonium than the public.
Thus, doses for the population
exposed to the Hanford releases are probably not high enough to result in detectable
increases in disease rates. This does not mean that there is no increase in risk. Rather, it
is very difficult to detect anything other than very large increases in risk. This is due to the
limitations of existing information and the methods that epidemiologists have available to them.
Most studies that have measured plutonium uptake by the potentially exposed
public have been inconclusive or have not found increased levels of plutonium in human
tissues that could be attributed to the operations of weapons facilities (Cobb 1982, Nelson
1993). Unfortunately, in recent years the emphasis of programs that were monitoring the
amount of plutonium taken up by the public and by workers has shifted almost exclusively
to only monitoring nuclear workers (Nelson 1993).
Iodine-131
Potential risks associated with iodine-131 are a
serious concern. Researchers have found an increased rate of thyroid growths in people who were
exposed as children. Their doses
were as low as nine rads (Ron 1989).
The thyroid easily absorbs iodine-131 through the food chain. Scientists have recently
identified an increased thyroid cancer incidence among people in Los Alamos County, New Mexico.
No one has begun a comprehensive dose reconstruction at Los Alamos. The sustained
high level of thyroid cancer in a population living near that nuclear weapons plant is
cause for concern.
There is a low chance of dying from thyroid cancer because it can be
successfully treated. Because of this, researchers should study cancer incidence rather
than cancer deaths to determine if increased risks of thyroid cancer are present. A further
complication in determining risk is that many tumor registries do not collect information on benign growths or other
types of illnesses. Studies show that there is also an increase in benign growths among
radiation-exposed individuals. Other thyroid abnormalities may be present. Thus, the sum
of thyroid problems which may be due to
iodine-131 exposure will be difficult to determine.
Conclusion
A valid estimate of the health risk posed by Hanford releases will require
accurate individual dose estimates,
accurate measures of disease incidence and at least a moderate number of affected
individuals. Risk estimates may only be possible for thyroid disease from exposure to
iodine-131. For other health problems and for other radioactive materials, valid estimates
of disease rates and exposure levels are unlikely. Because exposures from Hanford are
unique, comparisons with other exposures, other health problems or animal studies may
be of limited value and often misleading.
Selected References
Cobb, J.C., B.C. Eversole, P.G. Archer, et al. "Plutonium Burdens in People Living
Around the Rocky Flats Plant." Final Report submitted to Environmental Monitoring
Systems Laboratory, U.S. Environmental Protection Agency, P.O. Box 15027, Las Vegas,
NV 89114. June 1982.
Gilbert, E.S., G.R. Petersen, J.A. Buchanan, "Mortality of Workers at the Hanford Site:
1945-1981." Health Physics: 1989; 56:11-25.
Nelson, I.C., V.W. Thomas, R.L. Kathren, "Plutonium in South-Central Washington
State Autopsy Tissue Samples: 1970-1975." Health Physics: 1993; 64 (4):
422-428.
Ron, E., B. Modan, D. Preston, et al. "Thyroid Neoplasia Following Low-Dose
Radiation in Childhood." Radiation Research: 1989; 120: 516-531.
Wilkinson, G.S., G.L. Tietjen, L.D. Wiggs, et al. Mortality Among Plutonium and Other
Radiation Workers at a Plutonium Weapons Facility. American Journal of
Epidemiology: 1987; 125: 231-250.
Published Summer 1994
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