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Testimony of Steve Wing to US House of Representatives
Statement to the Subcommittee on Energy and Environment of the Committee on
Science, United States House of Representatives, July 18, 2000
Steve Wing, Associate Professor, Department of Epidemiology, School of
Public
Health, University of North Carolina
Mr. Chairman and Members of the Committee, thank you for inviting me to
testify
about health effects of low level radiation. I am an epidemiologist on the
faculty at the University of North Carolina where I have studied radiation
health effects among workers at Oak Ridge, Los Alamos, Hanford and Savannah
River under funding from the Departments of Energy and Health and Human
Services. Epidemiology, the study of disease in human populations, is
especially important in risk estimation and standard setting because animal
and
laboratory studies necessitate extrapolation from high to low doses, from
molecules and cells to organisms, and from other species to humans (1-3).
We know that ionizing radiation can cause cancer and inherited mutations by
damaging DNA. Although epidemiologists have studied populations exposed to
both
high and low levels of radiation, extrapolation of risks from high to low
doses
has led to a debate over whether a straight line extrapolation, the linear
no-threshold model, is appropriate. My testimony will make three points:
current cancer risk estimates are too low by a factor of ten or more;
current
standards do not adequately protect workers and the public; and, a large
and
growing body of scientific evidence shows that there is no basis for
further
relaxation of radiation protection standards.
Extrapolation from high dose studies.
High dose studies examine special populations including patients receiving
radiation treatments. By far the most influential are studies of survivors
of
the bombings of Hiroshima and Nagasaki that are currently the primary basis
for
cancer risk estimates. However, the A-bomb studies are flawed due to
selective
survival, poor dose measurement and confounding exposures (4-7).
The atomic bombings produced massive immediate casualties as well as
delayed
deaths due to lingering effects of radiation, infectious epidemics, and the
destruction of food, housing, and medical services (8). Only the
healthiest
survived these conditions, especially among those who are most vulnerable,
the
young and the old. By 1950, when a list of survivors was assembled for
long-term study, persons most susceptible to radiation had already died.
The
healthy survivor effect leads to underestimation of risks, particularly for
exposures in utero, during childhood, and at older adult ages (6).
Detection of radiation risks depends upon the ability of an epidemiological
study to classify persons according to their exposure levels. A-bomb
survivors
were not wearing radiation badges, therefore their exposures had to be
estimated
by asking survivors about their locations and shielding at the time of
detonation. In addition to the typical types of recall bias that occur in
surveys, stigmatization of survivors made some reluctant to admit their
proximity (9). Acute radiation injuries such as hair loss and burns among
survivors who reported they were at great distances from the blasts (10,
11)
suggests the magnitude of these errors, which would lead to under
estimation of
radiation risks.
Another bias occurs because of the higher exposures of distant survivors to
residual radiation. Fallout affected distant survivors in both cities (8,
12).
In addition, survivors who were shielded or exposed at greater distances
were
strong enough to enter the areas near the hypocenters of the blasts within
hours
of detonation, exposing themselves to residual radiation created by the
atomic
weapons (8, 12-14). Residual radiation exposures of lower dose survivors
leads
to an underestimate of radiation risks.
Direct observation from low dose studies.
In 1956 Dr. Alice Stewart and colleagues reported in The Lancet that fetal
exposures during obstetric x-ray examinations are associated with elevated
childhood cancer rates (15). The fetus is especially sensitive to
radiation due
to rapid cell division. Stewart's findings have been replicated in
numerous
other low dose studies (6, 16-18), and standards for medical practice now
dictate that small doses of radiation associated with a single x-ray should
be
avoided during pregnancy.
Long-term studies of cancer among nuclear workers began to appear in the
1970s
when Mancuso, Stewart and Kneale reported that small doses of radiation
received
at older ages raised cancer rates among workers at the plutonium production
facility in Hanford, Washington (19). Manhattan Project scientists
realized in
the early 1940s that workers in the weapons plants faced special hazards,
and
they created a unique resource for health studies at some facilities by
issuing
each employee a radiation monitor that was incorporated into the security
badge
required at work. Although dose records are poor for many workers and
veterans,
long-term studies of well-monitored workers have now been reported from
nuclear
facilities in the U.S., the United Kingdom and Canada. Despite the fact
that
workers are generally healthy adults, many of these studies have
demonstrated
relationships between low level radiation and cancer death, particularly
among
older workers. The greater sensitivity of older adults to ionizing
radiation
was not recognized in A-bomb studies due to selective survival, however
this
observation is consistent with studies that show reductions in immune
function
and efficiency of DNA repair with aging (6, 20). Risk estimates from many
occupational studies are approximately 10 times higher than estimates based
on
follow-up of A-bomb survivors (21-33), showing that current protection
standards
are too lax. In our recent study of multiple myeloma among Oak Ridge,
Hanford,
Los Alamos and Savannah River workers, doses between 5 and 10 rems were
associated with a threefold elevated risk, and doses over 10 rems were
associated with a fivefold elevated risk (33). None of the multiple
myeloma
cases had recorded doses over the current U.S. occupational limit of five
rems
per year.
From the United Kingdom comes evidence that paternal preconception
exposures are
associated with risk of childhood cancer, stillbirth and an excess of male
compared to female births (34-36). The ability of radiation to induce
heritable
genetic mutations in experimental animals has been recognized since the
1920s
(37). This recent evidence suggests that small doses of radiation
delivered in
the period prior to conception can lead to genetic effects in human
offspring.
Evidence on genomic instability following exposure to alpha radiation
raises
concerns for both carcinogenic and inherited genetic effects (38-40).
The belief that radiation risks at low doses could be extrapolated from
high
dose studies led some to predict that cancer risks of radiation could not
be
detected among nuclear workers. Although this has turned out to be false,
some
researchers have pooled data from different worker populations in order to
increase sample size, believing that this would increase power to detect
radiation risks (41-43). Unfortunately, pooling populations with different
types of radiation, exposure conditions, measurement qualities and worker
selection factors, achieves statistical precision at the cost of accuracy,
diluting radiation effects (43).
Diseases and genetic mutations caused by radiation do not carry a marker
showing
their origins, therefore epidemiologists look for excess rates of disease
in
populations with higher radiation exposures. However, it is easy to design
an
epidemiological study of environmental or occupational radiation exposure
that
is unable to detect low level effects. Only in special circumstances, such
as
the cases of well-monitored workers and certain medical exposures (44), is
it
possible to quantify low doses and subsequent risk. The sensitivity of
epidemiological studies is compromised because people generally cannot be
traced
between the time they are exposed and the time disease develops, and
because
medical information (other than cause of death) is not routinely available
for
populations without universal medical care. It is incorrect to conclude
that
low level radiation is safe on the basis of studies that lack careful
radiation
measurements and follow-up of medical outcomes. Unfortunately such
conclusions
have been made based on studies of geographic variation in average
background
radiation (45).
Furthermore, some scientists have mistakenly claimed that there is no
evidence
of radiation health effects below some arbitrary level. Not only do such
statements ignore an extensive medical literature on in utero and
occupational
radiation; they reflect a basic misunderstanding of how epidemiology
works. In
order to detect the risks from a hazardous agent, epidemiologists study a
range
of exposure levels. For example, we compare lung cancer rates of
never-smokers
to rates among people who smoke less than a pack a day, one pack a day, two
packs a day, and three or more packs a day. It would be incorrect to
separate
the data for people who smoke one cigarette a day and declare that low
levels of
smoking are safe. Conclusions about health effects of agents such as
radiation
and cigarettes should be derived from data on a range of exposures.
The current state of knowledge
As knowledge about ionizing radiation has grown, health effects have been
recognized from activities that until recently were thought to be safe.
Despite
past assurances about the safety of nuclear weapons tests, the National
Cancer
Institute's recent study indicates that tens of thousands of Americans can
expect to get thyroid cancer from just one of the radionuclides released by
atmospheric testing (46). The fact that radiation protection standards
have
been reduced as scientific study of low doses increases is another measure
of
concern (7). Although the International Commission on Radiation Protection
recommended in 1990 that the 5 rem per year limit for nuclear workers be
reduced
to 2, the U.S. continues to permit workers to be exposed to more than twice
the
radiation dose allowed by countries that adopted the international
standard,
including Canada and the European Union.
The nuclear age is little more than a half-century old. Although much has
been
learned about radiation during this time, there is much more that remains
to be
understood about human health effects. It is increasingly clear that there
is
great variability in the sensitivity of humans to low level radiation due
to
factors such as age, genetic susceptibility and exposures to chemical
agents,
infection or nutritional factors. Decisions about exposure standards
should
take account of the special risks faced by the young, the old and the
genetically susceptible. Public health and moral principles demand that we
protect the most vulnerable.
As amply documented by the Secretarial Panel for the Evaluation of
Epidemiologic
Research appointed by Admiral Watkins (47), President Clinton's Advisory
Committee on Human Radiation Experiments (48), a taskforce of the
Physicians for
Social Responsibility (49), and numerous publications in the scientific
literature (50-54), the body of scientific knowledge about the health
effects of
ionizing radiation has been compromised by concerns about secrecy and
public
relations. In its 1995 report, the President's Advisory Committee on Human
Radiation noted that, "By the mid-1960s the possibility that data gathering
could only get the AEC (Atomic Energy Commission) into more trouble became
an
incentive to 'not study at all'" (48). These attitudes have continued to
affect
research in recent decades (51, 52). In the case of regulatory standards
that
are intended to protect the health of workers and the public, policy makers
should consider scientific evidence and testimony with the understanding
that
scientists have been restrained from fully investigating the effects of low
level ionizing radiation.
Current radiation standards already fail to adequately protect workers and
the
public, even if flawed risk estimates from A-bomb studies are used. The
1994
GAO report on Nuclear Health and Safety notes that exposures permitted by
current Nuclear Regulatory Commission and Department of Energy guidelines,
according to those agencies, would lead to 1 in 300 premature cancer deaths
in
the general public and 1 in 8 among workers (55). No other carcinogens are
permitted such lax standards. I strongly urge members of Congress and the
regulatory agencies to exercise precaution and prudence in order to protect
the
health and lives of the public and of future generations who will be
affected by
decisions on production and disposition of nuclear materials.
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