Exposure to nitrosamines, carbon black, asbestos, and talc and mortality from stomach, lung, and laryngeal cancer in a cohort of rubber workers

Our plain-English summary of Exposure to nitrosamines, carbon black, asbestos, and talc and mortality from stomach, lung, and laryngeal cancer in a cohort of rubber workers, by K. Straif, U. Keil, D. Taeger, et al (American Journal of Epidemiology, 2000).

The study

• Authors: K. Straif, U. Keil, D. Taeger, D. Holthenrich, Y. Sun, M. Bungers, S.K. Weiland
• Journal: American Journal of Epidemiology
• Published: 2000;152(4):297-306
• Cited by: 52 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

There is sufficient evidence for an excess occurrence of stomach and lung cancer among rubber workers. However, evidence for causal associations with specific exposures is still limited. A cohort of 8,933 male German rubber workers was followed for mortality from January 1, 1981 through December 31, 1991. Work histories were reconstructed using routinely documented cost center codes. For each cost center code, calendar time-and plant-specific levels of exposure to nitrosamines, asbestos, talc (low, medium (m), and high (h)), and carbon black (two levels) were estimated by industrial hygienists. Rate ratios (RR) and 95% confidence intervals (CI) were calculated using Cox proportional hazards models, with the lowest exposure level used as the reference category. Exposure was lagged 10 years to account for latency. Exposure-response relations between exposure to asbestos and lung cancer mortality (RRm = 1.3, 95% CI: 0.9, 1.9; RRh = 2.0, 95% CI: 0.9, 4.1) and between exposure to dust (talc and asbestos combined) and stomach cancer mortality (RRm = 1.8, 95% CI: 0.9, 3.8; RRh = 2.7, 95% CI: 1.0, 7.1) were observed. Exposure to nitrosamines was not associated with mortality from stomach or lung cancer. These results suggest that the increased mortality from lung and stomach cancer among rubber workers is associated with exposure to asbestos and dust, respectively.

In plain English

This retrospective cohort study followed 8,933 male blue-collar workers at five German rubber plants, hired in or after 1950, for deaths from 1981 through 1991. Industrial hygienists estimated past exposure to nitrosamines, asbestos and talc (low, medium, high) and carbon black (exposed or not) for each work area. The article does not name asbestos fiber types. Lung cancer deaths were above the western German rate (154 deaths; standardized mortality ratio 123, 95% CI 104 to 144). Within the cohort, the lung cancer rate ratio was 1.3 (0.9 to 1.9) for a combined category of medium asbestos or medium or high talc exposure, and 2.0 (0.9 to 4.1) for high asbestos exposure. Stomach cancer rate ratios rose with talc- and asbestos-containing dust: 1.8 (0.9 to 3.8) for medium and 2.7 (1.0 to 7.1) for high. Exposure to nitrosamines was not associated with deaths from stomach or lung cancer. Laryngeal cancer results rested on only 8 deaths. The authors had no smoking data. They concluded that their results support the possibility of associations between asbestos and lung cancer, and between dust and stomach cancer, among rubber workers.

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 study, with internal comparisons using Cox proportional hazards models (exposure lagged 10 years) and comparison with the general population using standardized mortality ratios

• Who was studied: 8,933 male German blue-collar workers in five rubber plants. All were hired during or after 1950 and were alive and actively employed or retired on January 1, 1981. They were followed for mortality from January 1, 1981 to December 31, 1991. At the start of follow-up the cohort included 6,875 active workers and 2,058 retirees.

• Exposure: Industrial hygienists estimated exposure to total nitrosamines, asbestos and talc (low, medium, high) and carbon black (exposed vs not exposed) for each cost center code, by calendar time and plant. Asbestos fiber types are not specified.

• **High asbestos exposure** included raw material storage, weighing and mixing; use of asbestos as filler; cleaning and repair of jute bags; and sewing asbestos-containing gloves.

• **Medium asbestos exposure** was wearing asbestos-containing heat-protective clothing.

• **Measurements:** one reported measurement in a plant's main mixing area in 1976 was 0.13–0.26 mg/m3, which the authors equated to about 5 fibers/cm3.

• **Talc:** the authors note that talc may be contaminated by asbestos.

• Main results:

  • Compared with the male population of western Germany, the whole cohort had these standardized mortality ratios:

• **Lung cancer:** 123 (95% CI 104, 144), 154 deaths.

• **Stomach cancer:** 117 (85, 157), 44 deaths.

• **Laryngeal cancer:** 117 (50, 230), 8 deaths.

  • In bivariate analyses, the highest lung cancer risk was seen with high asbestos exposure:

• **Categorization 1** (at least 1 year at high exposure): hazard rate ratio 1.8 (95% CI 1.0, 3.3), 13 deaths.

• **Categorization 2** (at least 10 years at high exposure): 2.2 (1.1, 4.5), 9 deaths.

  • In multivariate models, the combined asbestos/talc variable showed an exposure-response relation with lung cancer. Its medium category combined workers with medium asbestos exposure or medium or high talc exposure. Its high category was high asbestos exposure.

• **Categorization 1:** medium rate ratio 1.3 (95% CI 0.9, 1.9); high 2.0 (0.9, 4.1).

• **Categorization 2:** medium 1.1 (0.8, 1.6); high 2.0 (0.8, 5.4).

The adjusted carbon black estimate was markedly reduced (1.1, 95% CI 0.7, 1.9).

• In multivariate models, stomach cancer mortality increased with exposure to talc- or asbestos-containing dust. The medium category combined workers with medium or high asbestos exposure or medium talc exposure.

• **Categorization 1:** medium rate ratio 1.8 (95% CI 0.9, 3.8); high 2.7 (1.0, 7.1).

• **Categorization 2:** medium 1.9 (0.9, 4.0); high 3.9 (1.2, 12.6).

  • In bivariate analyses of asbestos alone and stomach cancer, the increased risks were not statistically significant:

• **Medium exposure:** hazard rate ratio 1.5 (95% CI 0.8, 2.9).

• **High exposure:** 1.5 (0.5, 5.0).

Both figures are from exposure categorization 1.

• Exposure to nitrosamines was not associated with mortality from lung or stomach cancer. The estimates did not change significantly after adjustment or after changing cutpoints.
• There were 8 laryngeal cancer deaths. Hazard rate ratios for asbestos were 2.3 (95% CI 0.5, 10.2) for medium and 4.7 (0.5, 42.8) for high exposure. Only high talc exposure (5.4; 1.1, 27.0) and carbon black exposure (5.3; 1.3, 21.4) were statistically significant. Because of the few deaths, no further analyses were performed.
• The authors' conclusion: The authors concluded that their results support the possibility of associations between asbestos exposure and increased lung cancer mortality, and between dust exposure and increased stomach cancer mortality, among rubber workers. They found that increased carbon black risks in bivariate models seemed confounded by asbestos and talc. They found no association between nitrosamines and mortality from stomach or lung cancer. Laryngeal cancer findings were consistent with the lung cancer results, but there were too few deaths for firm conclusions.
• Limitations the authors state:
  • No data were available to directly assess confounding by smoking.
  • Residual confounding is possible from smoking and from other rubber-industry exposures that were not part of the exposure assessment.
  • There was no environmental monitoring before 1979, so exposures were retrospective semiquantitative expert estimates.
  • The authors knew of only a few asbestos measurements in the plants before 1980.
  • Dust was not measured or directly estimated. Talc exposure was used as an indicator of dust.
  • Carbon black exposure was only classified as exposed vs not exposed.
  • The small number of laryngeal cancer deaths precluded firm conclusions.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Stomach cancer, Talc and vermiculite, Throat and laryngeal cancer.

Medical terms in this study, explained in our Lexicon: Talc, Laryngeal Cancer, Lung Cancer, rate ratio, confidence interval, Latency, Stomach Cancer.

Related studies

• Occupational risk factors for mortality from stomach and lung cancer among rubber workers: an analysis using internal controls and refined exposure assessment — K. Straif, L. Chambless, et al. (1999)
• Stomach Cancer and Exposure to Talc Powder without Asbestos via Chinese Herbal Medicine: A Population-Based Cohort Study — C.J. Chang, Y.H. Yang, et al. (2019)
• Workplace risk factors for cancer in the German rubber industry: Part 1. Mortality from respiratory cancers — S.K. Weiland, K. Straif, et al. (1998)
• Talc exposure and risk of stomach cancer: Systematic review and meta-analysis of occupational cohort studies — C.J. Chang, Y.K. Tu, et al. (2020)
• Talc-treated rice and Japanese stomach cancer — R.R. Merliss (1971)
• Talc-coated rice as a risk factor for stomach cancer — G.N. Stemmermann, L.N. Kolonel (1978)

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