Cancer risks and low-level radiation in U.S. shipyard workers

Our plain-English summary of Cancer risks and low-level radiation in U.S. shipyard workers, by G.M. Matanoski, J.A. Tonascia, A. Correa-Villaseñor, et al (Journal of Radiation Research, 2008).

The study

• Authors: G.M. Matanoski, J.A. Tonascia, A. Correa-Villaseñor, K.C. Yates, N. Fink, E. Elliott, B. Sanders, D. Lantry
• Journal: Journal of Radiation Research
• Published: 2008;49(1):83-91
• Cited by: 28 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The risks for four cancers, leukemia, lymphopoietic cancers (LHC), lung cancer and mesothelioma, were studied in workers from shipyards involved in nuclear powered ship overhauls. The population represented a sample of all workers based on radiation dose at study termination. The final sample included 28,000 workers with > or = 5.0 mSv, 10,462 workers with < 5.0 mSv and 33,353 non-nuclear workers. Nuclear workers had lower mortality rates for leukemia and LHC than US white males but higher rates of lung cancer and a significant five-fold excess of mesothelioma. Dose-dependent analyses of risks in the high exposure group indicated that for each cancer the risk increased at exposures above 10.0 mSv. An internal comparison of workers with 50.0 mSv exposures to workers with exposures of 5.0-9.9 mSv indicated relative risks for leukemia of 2.41 (95% CI: 0.5, 23.8), for LHC, 2.94 (95% CI: 1.0,12.0), for lung cancer, 1.26 (95% CI: 0.9, 1.9) and for mesothelioma, 1.61 (95% CI: 0.4, 9.7) for the higher exposure group. Except for LHC, these risks are not significant. However, the increasing risk with increasing exposure for these cancers, some of which are known to be related to radiation, suggests that low-level protracted exposures to gamma rays may be associated with these cancers. Other agents such as asbestos, which are common to shipyard work, may play a role especially in the risk of mesothelioma. Future follow up of the population would identify bounds on radiation risks for this population for comparison with similar risks estimated from other populations.

In plain English

This lecture note reported a preliminary analysis of deaths among workers at seven U.S. shipyards that overhauled nuclear-powered ships, followed to January 1982. The authors studied a stratified random sample of white male workers: 28,000 nuclear workers with lifetime radiation doses of 5.0 mSv or more, 10,462 with less than 5.0 mSv, and 33,353 non-nuclear workers. The radiation was low-level gamma radiation, mainly from cobalt-60. Compared with US white males, mesothelioma death rates were higher in all three groups: the standardized mortality ratios were 5.11 and 5.75 in the two nuclear groups and 2.41 in non-nuclear workers. Among nuclear workers, those with 50 mSv or more had a mesothelioma relative risk of 1.61 (95% CI 0.4 to 9.7) compared with 5.0 to 9.9 mSv. This was not statistically significant. Of the four cancers, only lymphatic and hematopoietic cancers showed a significant increase at higher doses. The authors suggested that asbestos may explain the mesothelioma pattern, and that radiation may be associated with these cancers. They noted small case numbers, short follow-up, missing smoking data, and no control for specific exposures such as asbestos.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Preliminary retrospective cohort mortality study of a stratified random sample of shipyard workers, presented as a lecture note. It compared death rates with US white males and with workers at different radiation dose levels.
• Who was studied: White male workers at seven U.S. Navy and private shipyards that overhauled nuclear vessels, followed to January 1982. The sample included 28,000 nuclear workers with 5.0 mSv or more, 10,462 nuclear workers with less than 5.0 mSv (about 20% of that group), and 33,353 non-nuclear workers (about 30%). Women and African-Americans were excluded.
• Exposure: Low-level, prolonged external gamma radiation, mainly from cobalt-60 in neutron-activated corrosion products, measured with individual dosimeters. Asbestos was discussed as a possible confounding shipyard exposure but was not measured. No fiber types are named.
• Main results:
  • Mesothelioma death rates compared with US white males were raised in all groups. The standardized mortality ratio was 5.11 (95% CI 3.03, 8.08; 18 deaths) for nuclear workers with 5.0 mSv or more, 5.75 (95% CI 2.48, 11.33; 8 deaths) for nuclear workers below 5.0 mSv, and 2.41 (95% CI 1.16, 4.43; 10 deaths) for non-nuclear workers.
  • Among nuclear workers with 5.0 mSv or more, the mesothelioma relative risk for 50 mSv or more versus 5.0 to 9.9 mSv was 1.61 (95% CI 0.4, 9.7) with no lag. The text rounds this to 1.6. It was not statistically significant.
  • The authors stated that the mesothelioma increases with dose could be related to differences in asbestos exposure. Pipefitters made up a higher share of nuclear workers (12%) than of non-nuclear workers (6%) in four shipyards.
  • For lymphatic and hematopoietic cancers, the relative risk for nuclear workers with 50 mSv or more versus 5.0 to 9.9 mSv was 2.94 (95% CI 1.0, 12.0) with no lag. With a 5-year lag it was 5.37 (95% CI 1.2, 48.7). The authors described these as significantly higher.
  • For leukemia, the relative risk for nuclear workers with 50 mSv or more versus the reference group was 2.41 (95% CI 0.5, 23.8). The authors described this as non-significant because of small numbers.
  • For lung cancer, the relative risk for nuclear workers with 50 mSv or more versus 5.0 to 10.0 mSv was 1.26 (95% CI 0.9, 1.9). Compared with US white males, only non-nuclear workers had a significantly higher lung cancer death rate, with a standardized mortality ratio of 1.15 (95% CI 1.02, 1.29).
  • All-cause death rates were significantly lower than in US white males only for the two nuclear groups. The standardized mortality ratio was 0.76 for 5.0 mSv or more and 0.81 for less than 5.0 mSv. For non-nuclear workers it was 1.00.
• The authors' conclusion: The authors concluded that the early data suggest the workers may have a risk of some cancers from low-dose radiation. They said asbestos may play a role, especially in mesothelioma, and that longer follow-up and adjustment for other job exposures are needed.
• Limitations the authors state:
  • Case numbers were small and only three dose groups were analyzed, which limits trend analysis.
  • Follow-up was short, with a median of about 13 years.
  • The job hazard index used to balance the groups was not meant to control for specific exposures such as asbestos. The authors said confounding by asbestos could explain the mesothelioma and lung cancer risks.
  • Smoking information was not available for all individuals.
  • Selection of healthier workers into nuclear work may bias comparisons between nuclear and non-nuclear workers. The authors called this an 'enhanced healthy worker effect'.
  • The group below 5.0 mSv could only be analyzed as a category, not in the dose-dependent analysis.
  • The results are preliminary, covering only seven shipyards and four selected cancers.

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Mesothelioma, Relative Risk.

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