Health Risks of Ionizing Radiation: - Clark University

146 Communities Near Nuclear Facilities
the facilities for long periods of time; these exposures
are very different from the acute exposures of, for
example, atomic bomb survivors.
Types of studies. Epidemiological studies of
these communities are particularly challenging. One
of the biggest problems confronting researchers is
the lack of exposure information. It is very difficult
to estimate an average dose for a community near a
facility and almost impossible to recreate individual
doses.
Since dose information is so hard to come by,
many researchers have adopted an ecologic approach
to studying these communities. People are grouped
according to where they live with the expectation
that people near a facility will show a particular
health effect more frequently than people far from
a facility. This is still a challenging approach for
several reasons including the fact that exposure
to radioactive emissions is unlikely to be a simple
function of distance. An airborne radioactive plume,
for example, might touch ground some distance
away from the plant, and over time radioactive
plumes may tend to travel in one direction according
to prevailing winds. Drawing a circle around a
facility and assuming that everyone inside was
potentially exposed, a common study design, is
overly simplistic.
Another problem involves legal limits on
radioactive releases. If plants are adhering to
exposure standards then doses received by the
public should be low and adverse health outcomes
are expected to be rare. The Nuclear Regulatory
Commission allows a maximum annual dose of 1
mSv to an exposed member of the public while EPA
allows a maximum dose of 0.1 mSv. These doses
are lower than average background radiation doses
of ~3 mSv and variations in background radiation,
in addition to variability in such factors as age and
exposure to other carcinogens, are very hard to
control for. This creates a ‘signal to noise’ problem
where the subtle health impacts of nuclear facilities
are hard or impossible to detect within the dramatic
variations in disease incidence of a community. If
exposure is truly below the regulatory limit, and
conventional risk models are reasonable, then we
should not expect to see obvious evidence of a health
impact.
It is important to remember that these studies
are very limited in what they can tell us: if no effect
is observed it might mean that there is no effect or
it might mean that the effect is too small to detect.
If an effect is observed, without dose information
and a dose-response relationship the result is often
insufficient to support causality.
12.2 US studies
Hanford. The Hanford site in Washington
produced plutonium for nuclear weapons from
the 1940s to the mid 1980s. In the mid 1980s,
information was released that documented large
releases of iodine-131 and other radioactive
materials from 1944 to 1957. Studies of possible
health effects in surrounding communities began
soon after this information became available. The
most recent and comprehensive publication from
these efforts is the federal government’s Hanford
Thyroid Disease Study, performed by researchers
at the Fred Hutchinson Cancer Research Center
in Seattle (Davis et al. 2002). This is one example
of a study with dose estimates, and in this case the
estimated mean thyroid dose of 131 I was 17.4 cGy.
Out of 3,440 study participants, all exposed in
early childhood, 20 were diagnosed with thyroid
cancer and there was not a detectable significant
dose-response relationship. Non-cancerous thyroid
disease was also studied and again no significant
dose-response trends were detected. Despite being
a very expensive effort the study is inconclusive and
cannot rule out a relatively strong effect of Hanford
emissions 1 .
Studies conducted in collaboration between
downwind communities and scientists (in the
Northwest Radiation Health Alliance) have employed
informal community survey-based methods to assess
potential health impacts of Hanford. Grossman et al.
(1996) reported more miscarriages in hypothyroid
women than in women with normal thyroid hormone
1 It is interesting to note that Kerber et al. (1993) found positive results in a cohort of people exposed to the same mean
dose (~17 cGy) of 131 I from NTS fallout (see the fallout and thyroid cancer sections). Ruttenber et al. (2004) point
out that, due to substantial errors in accounting for uncertainty, the results of HTDS can be seen as consistent with
no effect or with a relatively strong effect.