Health Risks of Ionizing Radiation: - Clark University

76 Radiation Workers
Figure 6-5. A low-level solid waste burial ground at Oak
Ridge National Laboratory (http://www.doedigitalarchive.
doe.gov/ImageDetailView.cfm?ImageID=2001089&page=se
arch&pageid=thumb).
than 0.05 Sv there were no cases in the low-dose
group; the OR in this case was 0, with a 95% upper
confidence limit of 2.3. This study was therefore not
inconsistent with the estimate of Checkoway et al.
(1988) and was largely inconclusive.
Loomis and Wolf (1996) performed a separate
analysis of mortality in Y-12 workers, in this case
defining the cohort as all workers (including women
and nonwhite men) who were employed between
1943 and 1974. Uranium enrichment was done at Y-
12 until 1947 and workers employed in this project
were assessed separately. Results for the 1947-1974
employment cohort were predictably close to those
of Checkoway et al. (1988) 10 .
Steve Wing and colleagues (1991) published
a study of a cohort defined as X-10 workers hired
1943-1972 and followed through 1984. The addition
of several years of follow-up produced findings that
were quite different from earlier studies, particularly
a significantly positive SMR for leukemia (1.63;
1.08-2.35) that was even higher among workers
monitored for internal deposition of radionuclides
(2.23; 1.27-3.62). Dose-response curves were fit for
cancers generally and for lung cancer and leukemia;
lag times of 0, 10 or 20 years were assumed to test
the effect of time since exposure. The cancer trend
was significant at all lag times, but a 20-year lag
appeared to provide the most significant result, an
estimated ERR of ~5/Sv 11 . The lung cancer trend
was similar, with an ERR of ~5.2/Sv, and this was
unaffected by choice of lag time. The leukemia doseresponse
trend was high (ERR ~9/Sv with 20-year
lag) but not significant. These estimates are much
higher than corresponding atomic bomb survivor
estimates and were not apparent in earlier studies
with fewer years of follow-up. The results were also
surprising because of the low level of exposure:
over 99.8% of annual reported doses were less than
50 mSv.
These researchers conducted another SMR
analysis of all workers employed 1943-1984, in
addition to cross-facility comparisons and a doseresponse
analysis (Frome et al. 1997). This analysis
was different in a few ways. The Wing et al. (1991)
analysis included both underlying cause of death
and ‘contributing cause’ of death in defining cases;
the new analysis only included underlying causes of
death. Dose categories were defined differently in
the newer study and some analytical methods were
changed. Finally, the dose-response analysis was
expanded to include workers at the Y-12 facility,
increasing the eligible cohort from 8,318 to 28,347.
This SMR analysis revealed excess lung cancer
mortality among white males (SMR 1.18) and
excess cancer of the large intestine among nonwhite
males (SMR 1.73); the leukemia excess was no
longer evident. The dose-response analysis revealed
significant, although lower, ERR estimates for
lung cancer (1.68/Sv; 0.03-4.94) and for all cancer
(1.45/Sv; 0.15-3.48). Cross-facility comparison
showed significant heterogeneity in lung cancer
and leukemia mortality rates; specifically, the X-10
facility showed unusually low lung cancer mortality
and unusually high leukemia mortality relative to
the Y-12 facility.
Oak Ridge and age at exposure. In 1999,
Richardson and Wing published two papers further
analyzing the Oak Ridge data, followed through
1990, and focusing specifically on the effect of
age. The first paper (Richardson and Wing 1999a)
only considered white males and found a significant
trend with age at exposure (see Figure 6-6).
10 Elevated SMRS of lung cancer (1.17; 1.01-1.34), prostate cancer (1.31; 0.91-1.81), CNS cancers (1.29; 0.79-2.00),
kidney cancer (1.30; 0.74-2.11) and ‘other lymphatic tissue’ (1.32; 0.82-1.99).
11 Reported as 4.94% increase per 10 mSv based on an exponential relative risk model.