Health Risks of Ionizing Radiation: - Clark University

0.10-4.71) while respiratory system cancers had a
nonsignificant estimate (ERR of 1.04/Gy; -0.89-
2.96).
A 2000 report (Ivanov et al. 2000) presented
risk estimates for non-cancer diseases among 68,309
workers. Significant dose-response relationships
were found for endocrine and metabolic disorders
(including thyroid disease, ERR 0.58/Gy), mental
disorders (ERR 0.4/Gy), nervous system disease
(ERR 0.35/Gy), digestive system disease (ERR
0.24/Gy), cerebrovascular disease (ERR 1.17/Gy)
and essential hypertension (ERR 0.52/Gy).
A 2001 report addressed mortality in 65,905
workers (Ivanov et al. 2001). Although mortality for
this group was no higher than for the general Russian
population, this could be explained by assuming
that the workers were healthier than average and
had a lower mortality risk before they were exposed
(the healthy worker effect). The authors did detect
significant dose-response relationships for malignant
neoplasms and cardiovascular disease. Using the
general Russian population as a control group they
determined that there was an ERR of 2.1/Sv (1.3-
2.9) for cancer mortality and 0.5/Sv (0.2-0.9) for
cardiovascular disease mortality.
We looked at two studies of the immune system
response of Chernobyl clean-up workers. Kurjane et
al. (2001) studied the immune status of 385 Latvian
clean-up workers exposed at Chernobyl. They found
evidence of impaired immune systems including
a reduction in T cells and neutrophil phagocyte
activity. The authors also detected altered levels
of certain antibodies. Kuzmenok et al. (2003) also
found evidence of impaired immune systems in 134
Belarussian cleanup workers although they found
normal numbers of T-cells.
Investigations into genetic damage in cleanup
workers have shown persistent damage in exposed
workers but have not shown clear evidence of
elevated mutations in the offspring of exposed
workers. Melnov et al. (2002) showed an apparent
increase in aberrations over time and Neronova
et al. (2003) found persistent 10-fold increases in
aberrations up to 13 years after exposure. Mutations
in the germ cells of exposed workers might be passed
on to offspring. This has been seen in families living
near Chernobyl or the Semipalatinsk Test Site and it
has also been observed in mice (Dubrova et al. 2003).
Livshits et al. (2001) measured specific mutations in
Nuclear Power Accidents 133
183 children born to Chernobyl cleanup workers and
in 163 controls. Dose estimates were only available
for 28% of the cleanup workers and they ranged
from 0.05 to 1.2 Sv. No significant differences
were found between exposed and control families,
although children conceived within 2 months
of exposure showed a nonsignificant increase in
mutations compared to children conceived 4 months
after exposure or later. This is in agreement with
observations in mice that suggest that the most
sensitive time for this type of effect is during sperm
maturation. Kiuru et al. (2003) measured a group of
mutations (largely overlapping with the mutations
measured by Livshits et al.) in 192 Estonian families
with children born before and after the father was
exposed at Chernobyl. There was a nonsignificant
increase in mutations in the exposed group (children
born after the father’s exposure). This increase was
greater, and almost significant, for paternal external
doses between 20 and 30 cSv, with an OR of 3
(0.97-9.3). No effect of time between exposure and
conception was found.
Studies of these workers must be interpreted
with some caution because individual doses are not
known with much certainty. Another consideration,
potentially more important than uncertainty in doses,
is the fact these workers were screened for health
effects at a higher rate than average Russians. This
was because of the known occupational hazard that
they had been exposed to and it may have led to an
overestimate of the risk.
11.2.3 Childhood thyroid cancer
The most prominent health effect of the Chernobyl
accident has been childhood thyroid cancer. The
thyroid is a gland in the neck that uses iodine in
the synthesis of thyroid hormone. Since it can’t
distinguish between radioactive iodine and stable
iodine, iodine isotopes in fallout can accumulate
in the thyroid. This is particularly important in the
fast-growing thyroids of young children. The major
isotope involved is iodine-131 (I-131).
One 1997 review article commented on the initial
skepticism among the scientific community about
potentially substantial disease outcomes in people
living near Chernobyl; this eventually gave way to
a consensus acceptance of a dramatic increase in
childhood thyroid cancer (Schwenn and Brill 1997).