58
PLUTONIUM
3. HEALTH EFFECTS
never monitored for plutonium exposure), mortality rate ratios were not significant for deaths from cancer
(1.05, all causes of cancer) or all causes other than cancer (0.98). Mortality rate ratios
significantly
decreased in association with increasing effective dose equivalents for plutonium and external radiation
combined (trends for plutonium doses were not reported). However, when stratified by specific causes of
death, mortality rate ratios were not significantly elevated (p≥0.05) for the tissues that received the
highest plutonium radiation doses (lung, 1.12; liver, 0.85; bone, 0.00), nor were there significant positive
trends with radiation dose (external plus internal plutonium dose). The mortality rate ratio was
significantly elevated for breast cancer (7.66, p<0.01) and cerebrovascular disease (1.27, p<0.05).
McGeoghegan et al. (2003) examined cancer mortality in a cohort of female Sellafield workers (n=6,376),
from which a subset (n=837) of women who had been monitored for plutonium exposure was identified
as plutonium workers. This cohort overlapped considerably with that studied by Omar et al. 1999).
Effective dose equivalents to the lung from plutonium were estimated to have ranged up to 178 mSv
(mean: 3.45 mSv, 5
th
–95
th
percentile range: 0.36–8.89 mSv). Comparisons of mortality rates between
plutonium workers and other radiation workers yielded significantly elevated mortality rate
ratios for all
deaths (2.20, p<0.01), all cancers (3.30, p<0.01), breast cancer (3.77, p<0.05), circulatory disease (2.18,
p<0.05), and ischemic heart disease (4.46, p<0.01). Mortality rate ratios were not elevated for cancers in
tissues that received the highest plutonium radiation doses (lung, 2.36; bone; 0.00; digestive organs
including liver, 3.90). Excess relative risks (per Sv) were estimated for external radiation, but not for
plutonium, and were not statistically significant.
Collectively, the Omar et al. (1999) and McGeoghegan
et al. (2003) studies did not find elevated mortality rate ratios for the tissues that received the highest
plutonium radiation doses among plutonium workers compared to other radiation workers (lung, liver,
bone), and did not find significant positive trends in cancer mortality or incidence in these tissues with
plutonium radiation dose. Although both studies found elevated mortality rate ratios in
other selected
organ categories (e.g., breast cancer), the associations between these outcomes and plutonium exposure
are more uncertain, given the negative findings for lung, liver, or bone, and that other tissues, such as
breast, received a much smaller radiation dose. The findings for all cancers and breast cancer may also
have been influenced by the relatively low standardized mortality ratios (<100) for these end points in the
other radiation workers (the comparison cohort to the plutonium workers), indicative of a “healthy worker
effect”, that was not evident in the plutonium worker cohort.
Carpenter et al. (1998) examined cancer mortality in workers at U.K. nuclear facilities (n=40,761) from
which a subset (n=12,498), who had been monitored for plutonium exposure,
was identified as plutonium
workers. Plutonium exposures (i.e., Bq) or doses (i.e., Gy, Sv) were not included in this analysis;
however, the number of years since first monitored or the total number of years monitored were
59
PLUTONIUM
3. HEALTH EFFECTS
considered as surrogates for duration of plutonium exposures. Mortality rates for plutonium workers
were not significantly elevated when compared to workers who were never monitored for radiation
exposure (to any nuclide). However, when stratified by number of years since monitored or by number of
years monitored, significant trends were found for increasing mortality rate ratios (monitored
compared to
never monitored) for all cancers (p<0.05) in association with increasing years of monitoring.
U.S. Nuclear Facilities (Hanford, Los Alamos, Rocky Flats).
Lung cancer mortality in plutonium
workers employed at the Rocky Flats nuclear weapons plant has been examined in a case-control study
(Brown et al. 2004). Lung cancer cases (n=180) were employed at the Rocky Flats
facility for at least
6 months during the period 1952–1989, when plutonium pits were fabricated at the facility. The control
group (n=720) consisted of Rocky Flats workers who were matched with cases for age, birth, year, and
gender. Internal lung radiation doses in the cohort derived primarily from exposures to
239
Pu,
240
Pu,
241
Pu,
241
Am, and
238
U; however, 98% of the internal effective dose equivalents in cases (96% in controls) were
estimated to have come from Pu and
241
Am (inbred from
241
Pu). Estimated effective
dose equivalents for
internal -radiation (cases plus controls) ranged from 0 (54%) to >940 mSv (5%). In the full cohort, the
odds ratio for lung cancer mortality was significant for the internal lung dose strata 400–644 mSv, but
was not significantly elevated at higher doses; there was no significant trend with dose (2.71, 95% CI:
1.20–6.09); the odds ratios were <1 for most dose categories for persons employed for <15 or >25 years.
When the analysis was restricted to workers employed at the facility for 15–25 years, a significant trend
was evident for increasing odds ratio in association with increasing internal lung effective dose
equivalents; however, there was no evidence of a positive trend for those employed for <10 or ≥25 years.
Some of the highest exposures to plutonium at Los Alamos occurred during the period 1944–1945 (i.e.,
Manhattan Project) when occupational safety procedures for handling of plutonium were not as complex
or well-regulated as more recent procedures (Hempelmann et al. 1973). A small cohort of adult males
(n=26) who worked at the Los Alamos facility at that time have been followed and assessed for health
effects (Hempelmann et al. 1973; Voelz and Lawrence 1991; Voelz et al. 1997).
Based on urine
monitoring (up to 1994) and/or postmortem tissue analyses, plutonium body burdens ranged from 50 to
3,180 Bq (median: 565 Bq), and effective dose equivalents ranged from 0.2 to 7.2 Sv (median: 1.25 Sv;
Voelz et al. 1997). Mortality in the group was compared to that in a group of workers (n=876) employed
at Los Alamos during the same period who had no history or evidence of exposure to plutonium (Voelz et
al. 1997). At the time of the study (1994), seven deaths had occurred; three from cancer (bone, lung,
prostrate), two from diseases of the circulatory system, one from respiratory disease, and one from
external causes. The single bone cancer death greatly exceeded expected numbers (0.01 deaths;