Cancer and noncancer mortality among aluminum smelting workers in Badin, North Carolina

Our plain-English summary of Cancer and noncancer mortality among aluminum smelting workers in Badin, North Carolina, by E.S. McClure, P. Vasudevan, N. DeBono, et al (American Journal of Industrial Medicine, 2020).

The study

• Authors: E.S. McClure, P. Vasudevan, N. DeBono, W.R. Robinson, S.W. Marshall, D. Richardson
• Journal: American Journal of Industrial Medicine
• Published: 2020;63(9):755-765
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Badin, North Carolina, hosted an aluminum smelting plant from 1917 to 2007. The Concerned Citizens of West Badin reported suspected excess cancer mortality among former employees. This study aimed to investigate these concerns.

Methods: The study cohort was enumerated from United Steel Workers' records of workers employed from 1980 to 2007. Cause-specific mortality rates in the cohort were compared with North Carolina population mortality rates using standardized mortality ratios (SMRs), standardized by age, sex, race, and calendar period. We estimated cause-specific adjusted standardized mortality ratios (aSMRs) using negative controls to mitigate healthy worker survivor bias (HWSB). Standardized rate ratios (SRRs) were calculated to compare mortality rates between workers ever employed vs never employed in the pot room.

Results: All-cause mortality among Badin workers was lower than in the general population (SMR: 0.81, 95% confidence interval [CI]: 0.71-0.92). After adjusting for HWSB, excesses for all cancers (aSMR: 1.55, 95% CI: 1.10-2.21), bladder cancer (3.47, 95% CI: 1.25-9.62), mesothelioma (17.33, 95% CI: 5.40-55.59), and respiratory cancer (1.24, 95% CI: 0.77-1.99) were observed. Black males worked the highest proportion of their employed years in the pot room. Potroom workers experienced higher respiratory cancer (SRR: 2.99, 95% CI: 1.23-7.26), bladder cancer (SRR: 1.58, 95% CI: 0.15-15.28), and mesothelioma (SRR: 3.36, 95% CI: 0.21-53.78) mortality rates than never workers in the pot room.

Conclusions: This study responds to concerns of a group of former aluminum workers. The results, while imprecise, suggest excess respiratory and bladder cancers among pot room workers in a contemporary cohort of union employees at a US smelter.

© 2020 Wiley Periodicals LLC.

In plain English

This retrospective cohort study followed 754 hourly union members employed in 1980-2007 at the aluminum smelter in Badin, North Carolina, through 2017; 247 died. Without exposure measurements, the authors compared the workers with North Carolina rates, and compared ever with never pot room workers. Overall mortality was lower than expected (SMR 0.81, 95% CI 0.71-0.92). Mesothelioma (3 deaths, counted with pleural cancer) was 15.00 times expected (95% CI 3.82-40.82). Bladder cancer (4 deaths) had an SMR of 2.27 (95% CI 0.62-5.82). With a method meant to reduce bias from workers being healthier than the general population, the ratios were 1.55 (95% CI 1.10-2.21) for all cancers, 3.47 (1.25-9.62) for bladder cancer and 17.33 (5.40-55.59) for mesothelioma. Ever pot room workers had a higher respiratory cancer death rate than never pot room workers (2.99, 95% CI 1.23-7.26). For those with over 10 years there, the respiratory cancer ratio versus never pot room workers was 0.71 (95% CI 0.19-2.69), an uncertain estimate. The authors concluded that all cancer, bladder cancer and mesothelioma mortality were elevated. They noted small numbers, no exposure measurements and no smoking data.

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 occupational cohort mortality study, newly assembled from union records. It compared workers with state population rates (standardized mortality ratios, including versions adjusted with negative control causes of death) and compared ever versus never pot room workers (standardized rate ratios).
• Who was studied: 754 hourly United Steel Workers (Local 303) members employed at any time from 1980 to 2007 at the aluminum smelting plant in Badin, North Carolina (operated by Alcoa). The group was 94% male and 65% White; the large majority of the rest were Black. Deaths were traced through 31 December 2017 using the National Death Index; 247 had died.
• Exposure: Employment at an aluminum smelter (prebake method). No agent-specific exposure, industrial hygiene or job-specific data were available, so ever employment, and employment in the pot room, stood in for exposure. Asbestos is listed among the hazards of aluminum smelting, and former workers described concerns about asbestos, but asbestos exposure was not measured.
• Main results:
  • Whole cohort versus the North Carolina population: all-cause mortality was lower than expected (SMR 0.81, 95% CI 0.71-0.92; 247 deaths).
  • Whole cohort versus the North Carolina population: mesothelioma SMR 15.00 (95% CI 3.82-40.82), based on 3 deaths, with pleural cancer and mesothelioma counted together. Bladder cancer SMR 2.27 (95% CI 0.62-5.82), based on 4 deaths.
  • Whole cohort, after adjustment for healthy worker bias using negative control causes of death: all cancers adjusted SMR 1.55 (95% CI 1.10-2.21; 86 deaths).
  • Whole cohort, after the same adjustment: bladder cancer adjusted SMR 3.47 (95% CI 1.25-9.62; 4 deaths) and mesothelioma adjusted SMR 17.33 (95% CI 5.40-55.59; 3 deaths). Respiratory cancer adjusted SMR was 1.24 (95% CI 0.77-1.99; 24 deaths).
  • Ever pot room workers compared with never pot room workers: respiratory cancer death rate ratio 2.99 (95% CI 1.23-7.26), based on 13 versus 11 deaths.
  • Workers with over 10 years in the pot room had lower respiratory cancer mortality than never pot room workers (SRR 0.71, 95% CI 0.19-2.69). The authors reported no positive dose-response with pot room work.
  • Ever pot room versus never pot room workers: mesothelioma rate ratio 3.36 (95% CI 0.21-53.78), based on 1 versus 2 deaths. Bladder cancer rate ratio 1.58 (95% CI 0.15-15.28), based on 1 versus 3 deaths.
  • Black males spent 38.5% of their employed person-time in pot rooms, compared with 19.9% for White males, 15.6% for Black females and 7.6% for White females.
• The authors' conclusion: The authors concluded that, after adjusting for healthy worker survivor bias, the cohort had elevated all cancer, bladder cancer and mesothelioma mortality. They noted that the SMRs for bladder cancer and mesothelioma rest on small numbers, and that the findings are a foundation for future follow-up.
• Limitations the authors state:
  • Exposures were not measured or quantified.
  • Small numbers of some cancer deaths reduced precision and prevented stable race- and sex-specific analyses.
  • Many workers were younger at the end of follow-up than the typical age at which some diseases cause death.
  • No smoking or other behavioral health data were available.
  • Only hourly union members were included. Workers who moved to salaried jobs, moved away or retired were censored from the cohort.
  • Diseases were counted only if listed as the underlying cause on the death certificate, and death certificate coding can misclassify diseases.
  • Some negative control causes of death may themselves be affected by smelting exposures. The authors say this would likely weaken the adjusted estimates.
  • Family members, including those possibly exposed through laundering of pot room clothing, were not followed.

Topics

Medical terms in this study, explained in our Lexicon: standardized mortality ratio (SMR), rate ratio, confidence interval, Mesothelioma.

Related studies

• Epidemiologic evidence of cancer in aluminum reduction plant workers — A. Rönneberg, F. Langmark (1992)
• Mortality among North Carolina construction workers, 1988-1994 — E. Wang, J.M. Dement, et al. (1999)
• Lung cancer mortality and fibre exposures among North Carolina asbestos textile workers — D. Loomis, J.M. Dement, et al. (2009)
• Lung cancer mortality in North Carolina and South Carolina chrysotile asbestos textile workers — L. Elliott, D. Loomis, et al. (2012)
• Irregular opacities in the lung, occupational asthma, and airways dysfunction in aluminum workers — K.H. Kilburn, R.H. Warshaw (1992)
• Estimates of historical exposures by phase contrast and transmission electron microscopy for pooled exposure--response analyses of North Carolina and South Carolina, USA asbestos textile cohorts — J.M. Dement, D. Loomis, et al. (2011)

Browse more research in American Journal of Industrial Medicine, or return to medical research.