Lung Cancer Risks from Plutonium: An Updated Analysis of Data from the Mayak Worker Cohort

Abstract

Workers at the Mayak nuclear facility in the Russian Federation offer a unique opportunity to evaluate health risks from exposure to inhaled plutonium. Risks of mortality from lung cancer, the most serious carcinogenic effect of plutonium, were evaluated in 14,621 Mayak workers who were hired in the period from 1948–1982, followed for at least 5 years, and either monitored for plutonium or never worked with plutonium. Over the follow-up period from 1953–2008, there were 486 deaths from lung cancer, 446 of them in men. In analyses that were adjusted for external radiation dose and smoking, the plutonium excess relative risk (ERR) per Gy declined with attained age and was higher for females than for males. The ERR per Gy for males at age 60 was 7.4 (95% CI: 5.0–11) while that for females was 24 (95% CI: 11–56). When analyses were restricted to plutonium doses <0.2 Gy, the ERR per Gy for males at age 60 was similar: 7.0 (95% CI: 2.5–13). Of the 486 lung cancer deaths, 105 (22%) were attributed to plutonium exposure and 29 (6%) to external exposure. Analyses of the 12,708 workers with information on smoking indicated that the relationship of plutonium exposure and smoking was likely sub-multiplicative (P = 0.011) and strongly indicated that it was super-additive (P < 0.001). Although extensive efforts have been made to improve plutonium dose estimates in this cohort, they are nevertheless subject to large uncertainties. Large bioassay measurement errors alone are likely to have resulted in serious underestimation of risks, whereas other sources of uncertainty may have biased results in ways that are difficult to predict.

Solid cancer incidence other than lung, liver and bone in Mayak workers: 1948–2004

“…To allow for a latent period in a radiation effect, analyses were also performed using the cumulative external dose and internal liver dose lagged by 0, 5, 10, 15 and 20 years. Because of indications that some workers were monitored for plutonium as a result of suspected diseases, person-years were classified as unmonitored until 2 years following the first monitoring date (Sokolnikov et al , 2008; Gilbert et al , 2013). The data were fitted to the following model:…”

“…The results from all of these models showed that attained age, gender and smoking status were the most important factors in modelling the background rates for other solid cancer incidence. However, the parametric approach produced a slightly better description of the background rates compared with the non-parametric approach, and this approach has also been used in previous analyses of Mayak cohort studies (Skolnikov et al , 2008; Gilbert et al , 2013). The final model for the baseline risks included a function of the gender-specific logarithm of attained age, the logarithm of attained age squared and gender-specific smoking status.…”

“…Studies of the radiation workers at the Russian Mayak Production Association (Mayak PA) have provided information on risks from external exposures and internal exposures from plutonium (Shilnikova et al , 2003; Sokolnikov et al , 2008; Azizova et al , 2012; Gilbert et al , 2013). These studies have demonstrated significant association between cancer and non-cancer diseases and exposure to internal plutonium and external gamma ray.…”

Low-dose ionizing radiation increases the mortality risk of solid cancers in nuclear industry workers: A meta-analysis

“…Thus, our meta-analysis of the 27 independent observational studies provided strong evidence that LDIR increases solid cancer mortality risk, compared with control populations, despite the SMR being <1. Unfortunately, the large international cohort studies assessed the excess mortality risk of cancer using excess relative risk (ERR) rather than SMR (15,(31)(32)(33). We found that the high heterogeneity (I 2 =94.6%, P=0.00) in solid cancer mortality risk was attributed to the 6 complete studies, but there was enough evidence to conclude that LDIR could significantly increase brain and CNS cancer mortality risk (combined SMR=1.16; 95% CI: 1.02-1.31), regardless of whether the fixed-effects or random-effects model was used.…”

Dose Reconstruction for the Million Worker Study

“…The Mayak worker cohort includes 25,757 workers hired during the period from 1948–1982 in one of the main plants (nuclear reactors, radiochemical plant, plutonium production facility) or in auxiliary plants involved with water treatment or mechanical repair (Gilbert et al 2013). Nearly all workers have dosimeter records of external exposure; workers in the radiochemical and plutonium production facilities had potential for plutonium exposure, which is mainly derived from bioassay measurements.…”