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Collectively, the Mayak studies provide evidence for increased risk of cancer mortality (bone, liver, lung)
in association with increased internal plutonium-derived radiation dose and/or body burden, with
approximately 4-fold higher risks in females compared to males. Four studies
estimated lung cancer
mortality risk among Mayak workers and yielded similar estimates of excess relative risk per Gy of
internal lung dose. Gilbert et al. (2004) estimated the excess lung cancer mortality risk (per Gy attained at
age 60 years) for essentially the entire cohort of Mayak workers (n=21,790) to be approximately 4.7 per
Gy (95% CI: 3.3–6.7) in males, and 19 per Gy (95% CI: 9.5–39) in females. Adjustment for smoking,
based on risk estimates in subgroups for which smoking data were available, decreased these
estimates
only slightly: males, 3.9 per Gy (95% CI: 2.6–5.8); and females, 19 (95% CI: 7.7–51). Cancer mortality
risk was linearly related to plutonium radiation dose. Excess relative risk per Gy declined strongly with
attained age (Gilbert et al. 2004). Kreisheimer et al. (2003) examined lung cancer mortality risk for a
subset of male Mayak workers (n=4,212) and estimated smoking-adjusted excess relative risk to be
4.50 per Gy (95% CI: 3.15–6.10). Jacob et al. (2005) used a mechanistic (i.e., multi-stage physiological)
model to estimate smoking-adjusted lung cancer mortality risk in a similar cohort (n=5,058) and found
the excess relative risk to be 0.11 per Sv (95% CI: 0.08–0.17); the corresponding estimate in units of
absorbed radiation dose would be 2.2 per Gy (assuming a radiation weighting factor of 20 for
-radiation). An alternative model that treated smoking as a multiplicative risk factor (rather than
additive), yielded an estimated excess relative risk of 0.21 per Sv (95% CI: 0.15–0.35), which
corresponds to approximately 4.3 per Gy, very close to the estimates from Gilbert et al. (2004) and
Kreisheimer et al. (2003). Sokolnikov et al. (2008) estimated ERRs of 7.1 per Gy (95% CI: 4.9–10) in
males and 15 per Gy (95% CI: 7.6–29) in females at attained age of 60 years among 5,572 of the Mayak
workers with confirmed plutonium exposure. A significant dose-response was
noted and lung cancer risk
was reasonably described by a linear function. The ERR declined with attained age and age at first
plutonium exposure.
Risks of mortality and morbidity from bone and liver cancers have also been studied in Mayak workers
(Gilbert et al. 2000; Koshurnikova et al. 2000; Shilnikova et al. 2003; Sokolnikov et al. 2008; Tokarskaya
et al. 2006). Increasing estimated plutonium body burden was associated with increasing cancer
mortality, with higher risk in females compared to males. Gilbert et al. (2000) examined
liver cancer
mortality in a cohort of Mayak workers (n=11,000). Mean plutonium body burdens for the cohort were
estimated to have been 3.78 kBq in males and 6.05 kBq in females. The corresponding absorbed
radiation doses to liver were 0.47 Gy in males and 0.88 Gy in females. A model in which liver cancer
risk was treated as a quadratic function of plutonium body burden achieved better fit to the data than a
linear model. Relative risk for liver cancer for the entire cohort was estimated to be 17 (95% CI: 8.0–26)
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3. HEALTH EFFECTS
in association with plutonium body burdens >7.4 kBq; however, when stratified by gender, the relative
risk estimate for females was 66 (95% CI: 16–45) and higher than for males (9.2; 95% CI: 3.3–23).
Risk of bone cancer mortality in this same cohort (n=11,000) was estimated to be 7.9 (95% CI: 1.6–32)
in association with plutonium body burdens >7.4 kBq for males and females combined (Koshurnikova et
al. 2000).
Risks of leukemia mortality, in the same cohort, were not associated with internal plutonium
exposure (Shilnikova et al. 2003). Liver cancer risk was examined in a case-control study of Mayak
workers (Tokarskaya et al. 2006). The case group consisted of histologically-confirmed cases of
malignant liver tumors (n=44) diagnosed during the period 1972–1999. These were matched to members
of a control group (n=111) for years of birth, gender,
years of hire, and job assignments. Estimated
absorbed radiation doses to the liver from plutonium ranged from 0 to 16.9 Gy (the 4
th
quartile range was
0.54–16.9 Gy). When stratified by absorbed radiation dose to the liver, the odds ratio
for liver cancer was
11.3 (95% CI: 3.6–35.2) for subjects who experienced >2.0–5.0 Gy (relative to 0–2.0 Gy). Odds ratios
for hemangiosarcomas were 41.7 (95% CI: 4.6–333) for the dose group >2.0–5.0 Gy, and 62.5 (95% CI:
7.4–500) for the dose group >5.0–16.9 Gy. Sokolnikov et al. (2008) reported averaged-attained age
ERRs for liver cancer of 2.6 per Gy (95% CI: 0.7–6.9) for males and 29 per Gy (95% CI: 9.8–95) for
females, and averaged-attained age ERRs for bone cancer of 0.76 per Gy (95% CI: <0–5.2) for males and
3.4 per Gy (95% CI: 0.4–20) for females. Elevated risks for bone cancer were observed only for workers
with plutonium doses exceeding 10 Gy. For lung and bone cancer, the ERR declined with attained age,
and
for lung cancer, the ERR declined with age at first plutonium exposure.
U.K. Atomic Energy Authority and Atomic Weapons Establishment Workers. S
tudies of mortality of
plutonium workers at U.K. facilities are summarized in Table 3-2 (Carpenter et al. 1998; McGeoghegan et
al. 2003; Omar et al. 1999). Although several studies have examined mortality rates in workers at the
Sellafield nuclear facility (Douglas et al. 1994; McGeoghegan et al. 2003; Omar et al. 1999; Smith and
Douglas 1986), the McGeoghegan et al. (2003) and Omar et al. (1999) studies attempted to estimate risks
in association with plutonium exposures, as opposed to radiation exposures, in general. Omar et al.
(1999) identified a cohort of plutonium workers as a subset (n=5,203) of workers who had been
monitored at any time for exposure to plutonium (e.g., urinalysis). An analysis of monitoring data on
these subjects provided estimates of internal uptakes of plutonium (Omar et al. 1999).
Cumulative
internal uptakes were estimated to range from 0 to 12 kBq, with approximately 75% of the cohort having
cumulative uptakes ≤250 Bq. Cumulative radiation dose equivalents for plutonium were estimated to be
approximately 3,280 Sv for bone surfaces, 44.5–896 Sv for lung, and 421 Sv for liver; however,
analyses
of dose trends were of the combined dose equivalents from plutonium and external radiation. In a
comparison of mortality rates for plutonium workers compared to other radiation workers (i.e., those