Mortality among workers at the Savannah River Site

Our plain-English summary of Mortality among workers at the Savannah River Site, by D.B. Richardson, S. Wing, S. Wolf (American Journal of Industrial Medicine, 2007).

The study

• Authors: D.B. Richardson, S. Wing, S. Wolf
• Journal: American Journal of Industrial Medicine
• Published: 2007;50(12):881-91
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Workers employed at the Savannah River Site (SRS) were potentially exposed to a range of chemical and physical hazards, many of which are poorly characterized. We therefore compared the observed deaths among workers to expectations based upon death rates for referent populations.

Methods: The cohort included 18,883 SRS workers hired between 1950 and 1986. Vital status and cause of death information were ascertained through 2002. Sex-specific standardized mortality ratios (SMR) were computed using U.S. and South Carolina mortality rates. SMRs were tabulated separately for monthly-, weekly-, and hourly-paid men.

Results: Males had fewer deaths from all causes [SMR=0.80, 90% confidence interval (CI): 0.78, 0.82], all cancers (SMR=0.85, 90% CI: 0.81, 0.89), and lung cancer (SMR=0.88, 90% CI: 0.82, 0.95) than expected based upon US mortality rates. The SMR for cancer of the pleura was 4.25 (90% CI: 1.99, 7.97) for men. The SMR for leukemia was greater than unity for monthly-paid (SMR=1.33, 90% CI: 0.88, 1.93) and hourly-paid (SMR=1.36, 90% CI: 1.02, 1.78) men. Female workers had fewer deaths from all causes (SMR=0.75, 90% CI: 0.69, 0.82) than expected, but more deaths than expected from cancer of the kidney (SMR=2.58, 90% CI: 1.21, 4.84) and skin (SMR=3.90, 90% CI: 2.11, 6.61).

Conclusions: While the observed numbers of deaths in most categories of cause of death were less than expected, there are greater than expected numbers of deaths due to cancer of the pleura and leukemia, particularly among hourly-paid male workers. It is plausible that occupational hazards, including asbestos and ionizing radiation, contribute to these excesses.

In plain English

This retrospective cohort study followed 18,883 people (15,264 men and 3,619 women) hired by DuPont before 1987 at the Savannah River Site, a nuclear materials facility near Aiken, South Carolina, who worked at least 90 days. Deaths through 2002 were compared with numbers expected from US death rates. Workers had fewer deaths overall than expected. Men had more deaths than expected from cancer of the pleura: 7 deaths, a standardized mortality ratio (SMR) of 4.25 (90% confidence interval 1.99 to 7.97). Four of the seven were mechanics. No pleural cancer deaths occurred before the 1985 to 1989 period. Mesothelioma could be counted separately only for 1999 to 2002. It caused 2 deaths among men (SMR 0.92, 90% confidence interval 0.16 to 2.89), both among hourly-paid workers. Leukemia deaths were above expectation among hourly-paid men (39 deaths, SMR 1.36, 90% confidence interval 1.02 to 1.78). The authors noted there is little information on workers' exposure to asbestos and other chemicals at the site. They concluded it is plausible that occupational hazards, including asbestos and ionizing radiation, contribute to the pleural cancer and leukemia excesses.

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 cohort mortality study comparing observed deaths with expected deaths (standardized mortality ratios with 90% confidence intervals) based on US and, separately, South Carolina death rates
• Who was studied: 18,883 workers (15,264 men and 3,619 women) at the Savannah River Site near Aiken, South Carolina. They were hired by DuPont before 1987 and worked at least 90 days, and were followed for vital status through December 31, 2002. Men were analysed separately as monthly-paid, weekly-paid and hourly-paid workers.
• Exposure: Employment at a nuclear materials production site. Potential hazards included ionizing radiation, acids, solvents, asbestos and hydrazine. Asbestos fiber type is not named, and individual asbestos exposure was not measured. The authors refer to industrial hygiene reports, particularly about the Maintenance Department.
• Main results:
  • Male workers had more deaths from cancer of the pleura than expected from US rates: SMR 4.25 (90% CI 1.99, 7.97), based on 7 observed deaths. There were no pleural cancer deaths among women (0.06 expected).
  • Of the seven men who died of pleural cancer, four were mechanics, one an engineer, one a technician and one a power plant operator. All were hired before 1955.
  • The pleural cancer SMR among men was above 1 in every pay group: monthly-paid 2.28 (1 death; 90% CI 0.12, 10.82), weekly-paid 5.34 (2 deaths; 90% CI 0.95, 16.83) and hourly-paid 4.79 (4 deaths; 90% CI 1.64, 10.96).
  • Using South Carolina rates instead of US rates, the pleural cancer SMR among men was smaller: 2.82.
  • By length of employment, the largest pleural cancer excess among men was in those employed 30 or more years: SMR 9.23 (3 deaths; 90% CI 2.58, 24.5).
  • By calendar period, there were no pleural cancer deaths among men before 1985 to 1989, when there were 4 (SMR 12.55; 90% CI 4.29, 28.72). The 2000 to 2002 SMR of 30.29 rested on one death.
  • Mesothelioma could be analysed only for deaths in 1999 to 2002. Among men overall there were 2 deaths (SMR 0.92; 90% CI 0.16, 2.89), both among hourly-paid men (SMR 1.89; 90% CI 0.34, 5.96). There were none among monthly- or weekly-paid men.
  • Cancer of the peritoneum among men: 4 deaths, SMR 0.76 (90% CI 0.26, 1.73) using US rates. The authors described evidence of excess peritoneal cancer as less clear, with SMRs slightly above 1 by pay group using South Carolina rates and below 1 using US rates.
  • Lung cancer among men overall was below expectation (SMR 0.88; 90% CI 0.82, 0.95). It was above expectation among hourly-paid men (SMR 1.12; 90% CI 1.02, 1.22) and below among monthly-paid men (SMR 0.52). The authors said smoking differences are a plausible explanation, and occupational exposures could also contribute.
  • Leukemia deaths were above expectation among monthly-paid men (20 deaths; SMR 1.33; 90% CI 0.88, 1.93) and hourly-paid men (39 deaths; SMR 1.36; 90% CI 1.02, 1.78).
  • Women had fewer deaths overall than expected (SMR 0.75). They had more deaths than expected from cancer of the kidney (SMR 2.58; 90% CI 1.21, 4.84) and skin (SMR 3.90; 90% CI 2.11, 6.61).
• The authors' conclusion: The authors concluded that, although deaths in most categories were fewer than expected, there were more deaths than expected from cancer of the pleura and leukemia, particularly among hourly-paid men. They considered it plausible that occupational hazards, including asbestos and ionizing radiation, contribute to these excesses.
• Limitations the authors state:
  • Comparison with national or state death rates is affected by the healthy worker effect, which may hide harmful effects of workplace exposures.
  • The analyses did not separate workers by exposure level, so exposed and unexposed workers were mixed. This may dilute evidence of harm.
  • There was little information on exposures other than radiation, including asbestos.
  • Mesothelioma had no separate cause-of-death code before the tenth ICD revision, so mesothelioma results cover only deaths in 1999 to 2002.
  • Residual confounding by cigarette smoking is likely.

Topics

Medical terms in this study, explained in our Lexicon: standardized mortality ratio (SMR), confidence interval, Lung Cancer, Pleura.

Related studies

• Pulmonary abnormalities associated with occupational exposures at the Savannah River Site — T. Makie, D. Adcock, et al. (2005)
• Mortality patterns among electrical workers employed in the U.S. construction industry, 1982-1987 — C.F. Robinson, M. Petersen, et al. (1999)
• Mortality of older construction and craft workers employed at Department of Energy (DOE) nuclear sites — J.M. Dement, K. Ringen, et al. (2009)
• Mortality among North Carolina construction workers, 1988-1994 — E. Wang, J.M. Dement, et al. (1999)
• Mortality of older construction and craft workers employed at department of energy (DOE) nuclear sites: follow-up through 2011 — K. Ringen, J. Dement, et al. (2015)
• Surveillance of respiratory diseases among construction and trade workers at Department of Energy nuclear sites — J.M. Dement, L. Welch, et al. (2003)

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