Lung fibrosis in plutonium workers

Our plain-English summary of Lung fibrosis in plutonium workers, by L.S. Newman, M.M. Mroz, A.J. Ruttenber (Radiation Research, 2005).

The study

• Authors: L.S. Newman, M.M. Mroz, A.J. Ruttenber
• Journal: Radiation Research
• Published: 2005;164(2):123-31
• Type of article: Case report
• Cited by: 26 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

There have been few systematic studies of the non-malignant health effects of alpha-particle radiation in humans. Animal studies and a report on plutonium-exposed workers from Russia suggest an association between high doses to the lung from plutonium exposure and the development of fibrotic lung disease. Prompted by a case of lung fibrosis in a retired plutonium worker, we tested the hypothesis that plutonium inhalation increases the risk for developing chest radiograph abnormalities consistent with pulmonary fibrosis. We conducted a retrospective study of nuclear weapons workers that included estimating absorbed doses to the lung with an internal dosimetry model. Our study population consisted of 326 plutonium-exposed workers with absorbed lung doses from 0 to 28 Sv and 194 unexposed workers. We compared the severity of chest radiograph interstitial abnormalities between the two groups using the International Labour Organization profusion scoring system. There was a significantly higher proportion of abnormal profusion scores among plutonium-exposed workers (17.5%) than among unexposed workers (7.2%), P < 0.01. Lung doses of 10 Sv or greater conferred a 5.3-fold risk (95% CI 1.2-23.4) of having an abnormal chest X ray consistent with pulmonary fibrosis when compared with unexposed individuals after controlling for the effects of age, smoking and asbestos exposure. This study shows that plutonium may cause lung fibrosis in humans at absorbed lung doses above 10 Sv.

In plain English

This retrospective study asked whether inhaled plutonium was linked to chest X-ray signs of lung scarring (pulmonary fibrosis) in Rocky Flats nuclear weapons workers near Denver. It was prompted by a retired worker whose lung biopsy showed fibrosis. Analysis of his lung tissue found no increased silica, asbestos or metals. It compared 326 plutonium-exposed workers (estimated lung doses 0 to 28.0 Sv) with 194 unexposed workers. Asbestos exposure estimates were not available for all subjects, so pleural abnormalities on X-ray served as a stand-in. Abnormal X-rays were found in 17.5% of exposed and 7.2% of unexposed workers. After adjusting for age, smoking and pleural abnormalities, workers with lung doses of 10 Sv or greater had a 5.3-fold risk of an abnormal X-ray (95% CI 1.2 to 23.4). Odds ratios for lower doses were not statistically significant. In the same model, workers with pleural abnormalities had a 2.4-fold risk of an abnormal X-ray compared with those without (95% CI 1.2 to 4.5). The authors concluded that plutonium may cause lung fibrosis at absorbed lung doses above 10 Sv.

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: Retrospective study comparing plutonium-exposed and unexposed workers, with lung doses estimated by an internal dosimetry model; it includes a case report of the index case that prompted the study
• Who was studied: 520 workers at the Rocky Flats Plant near Denver, Colorado: 326 plutonium-exposed workers (all male) and 194 unexposed workers. They were predominantly male, white and non-Hispanic, with a median age of 64.9 years at the time of chest X-ray. The exposed group was significantly older (median 68.1 years) than the unexposed group (median 59.6 years).
• Exposure: Inhaled plutonium, measured as cumulative equivalent dose to the lung (in Sv). Doses were estimated with the CINDY code and the ICRP 30 respiratory tract model, using urine measurements and lung counts. Asbestos exposure was not measured directly; pleural abnormalities on chest X-ray were used as a surrogate marker.
• Main results:
  • Abnormal chest X-ray profusion scores (ILO 1/0 or greater) were found in 17.5% of plutonium-exposed workers (57 of 326) and 7.2% of unexposed workers (14 of 194), P less than 0.01
  • Controlling for age, sex and race, plutonium exposure overall conferred a 1.7-fold risk of an abnormal profusion score (95% CI 0.9 to 3.3)
  • In univariate models, compared with unexposed workers, the odds ratios were 2.8 (95% CI 1.4 to 5.3) for doses above 0 and below 1 Sv, 1.9 (0.9 to 4.2) for 1 to below 5 Sv, 3.8 (1.2 to 11.8) for 5 to below 10 Sv, and 7.7 (2.4 to 24.3) for 10 Sv or greater
  • In the multivariate model (368 subjects with complete data), adjusted for age, smoking and pleural abnormalities, workers with lung doses of 10 Sv or greater had a 5.3-fold risk (95% CI 1.2 to 23.4) compared with unexposed workers; 5 of 12 (41.7%) in that group had abnormal scores. Odds ratios for lower dose groups were 1.5, 0.9 and 1.7, none statistically significant.
  • In the same multivariate model, workers with pleural abnormalities (the surrogate for asbestos exposure) had a 2.4-fold risk of an abnormal profusion score compared with workers without them (95% CI 1.2 to 4.5). Pleural abnormalities were present in 27.8% of exposed and 5.0% of unexposed workers with data.
  • Ever-smokers had a 4.2-fold risk of an abnormal profusion score compared with never-smokers (95% CI 1.8 to 10.0)
  • Restricted to the 398 workers without pleural abnormalities, the odds ratio for doses of 10 Sv or greater was 5.0 when controlling for age (reported as statistically significant). When smoking was added, it remained 5.0, with a 95% confidence interval of 0.7 to 35.1.
  • Index case: a retired plutonium worker with an estimated cumulative lung dose of 23 Sv had biopsy-confirmed interstitial fibrosis. Microanalysis of his lung tissue showed no increased silica, asbestos or metals.
• The authors' conclusion: The authors concluded that plutonium may cause lung fibrosis in humans at absorbed lung doses above 10 Sv
• Limitations the authors state:
  • Risk did not rise steadily with dose. The confidence intervals do not exclude a linear dose-response, and the dosimetry model may not have estimated doses accurately at all exposure levels.
  • It is not known how using the newer ICRP 66 respiratory model would change the dose-response findings
  • The two groups differed in age because unexposed workers' most recent X-rays were usually taken when they left employment
  • Smoking histories were missing for most unexposed workers (available for only 43%). The authors' further analyses suggested little resulting bias.
  • Asbestos exposure was not measured directly; pleural abnormalities on X-ray were used as a surrogate
  • Few subjects were in the high-dose categories

Topics

Medical terms in this study, explained in our Lexicon: Fibrosis, Chest X-Ray, Pulmonary Fibrosis, Interstitial, Asbestos Exposure.

Related studies

• Lung cancer and internal lung doses among plutonium workers at the Rocky Flats Plant: a case-control study — S.C. Brown, M.F. Schonbeck, et al. (2004)
• Causes of death in a cohort of 260 plutonium workers — B. Gold, R.L. Kathren (1998)
• USTUR Special Session Roundtable-US Transuranium and Uranium Registries (USTUR): A Five-decade Follow-up of Plutonium and Uranium Workers — S.Y. Tolmachev, M.J. Swint, et al. (2019)
• The legacy of weapons grade plutonium production: Health status of Hanford complex workers who manage the waste — D. Cherry, E. Friedman, et al. (2021)
• Asbestosis: interstitial pulmonary fibrosis and pleural fibrosis in a cohort of asbestos insulation workers: influence of cigarette smoking — R. Lilis, I.J. Selikoff, et al. (1986)
• Season of birth and lung fibrosis among workers exposed to asbestos — T. Hannu, M.S. Jaakkola, et al. (2007)

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