Tyler asbestos workers: A mortality update in a cohort exposed to amosite

Our plain-English summary of Tyler asbestos workers: A mortality update in a cohort exposed to amosite, by J.L. Levin, A. Rouk, S. Shepherd, et al (Journal of Toxicology and Environmental Health. Part B, Critical Reviews, 2016).

The study

• Authors: J.L. Levin, A. Rouk, S. Shepherd, G.A. Hurst, J.W. McLarty
• Journal: Journal of Toxicology and Environmental Health. Part B, Critical Reviews
• Published: 2016;19(5-6):190-200
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The Tyler asbestos plant produced pipe insulation from 1954 to 1972 and exclusively used amosite asbestos. There were 1130 former workers of this plant during the period of operation. A death certificate mortality analysis was published regarding this plant in 1998 for the period through 1993. This study represents an update of the mortality analysis with additional certificates collected for deaths occurring through 2011.Searches of the National Death Index database were conducted in 2004 and again in 2013. At the time of the latter search, only deaths occurring through 2011 were available. In total, 265 distinct additional death certificates were secured and added to 304 available from the original study. After the new certificates were coded (ICD-9), data were analyzed using the Centers for Disease Control and Prevention Life Table Analysis System (LTAS) and standard mortality ratios (SMR) generated with 95% confidence limits (CL). LTAS constructs cause-specific mortality rates by age, gender, race, and person-time at risk, and compares observed rates with a referent population in order to derive SMR. A significant excess number of deaths due to nonmalignant respiratory disease (asbestosis) and from select malignant neoplasms were identified. There were in total 23 mesothelioma deaths (4% of deaths), with 16 pleural and 7 peritoneal. The SMR for malignant neoplasms of the trachea, bronchus, and lung was 244 (with 95% CL 196, 300), suggesting that exposed workers from this cohort were nearly 2.5-fold (244 %) more likely to die from this cause as the general referent population. The analysis also showed that exposures of short duration (<6 mo) produced significantly elevated SMR for all respiratory cancers, lung cancer, and pleural mesothelioma. There was a significant difference in median duration of exposure for mesothelioma types, confirming association of peritoneal mesothelioma with longer duration of exposure. Deaths due to intestinal cancer (predominantly colon; not including rectum) were also found in excess. The mortality experience of the Tyler cohort continues to be followed with great interest, given the exclusivity of exposure to amosite. Data confirm the inherent pathogenicity of this fiber type for nonmalignant disease as well as select cancers, particularly relevant given the importance of this amphibole's use in the United States.

In plain English

This study updated an earlier death-certificate analysis of the 1,130 people who worked at an asbestos pipe-insulation plant in Tyler, Texas. The plant ran from 1954 to 1972 and used amosite asbestos. The authors added deaths through 2011 and analyzed 569 death certificates. They compared these deaths with the number expected from a reference population, using standardized mortality ratios (SMR), where 100 means no excess. Lung cancer deaths were raised (SMR 244, 95% confidence interval 196 to 300). So were intestinal cancer deaths, all of them colon cancer (SMR 240, 146 to 370), and pneumoconiosis (asbestosis) deaths (SMR 481, 305 to 722). There were 23 mesothelioma deaths: 16 pleural and 7 peritoneal, about 4% of all deaths. Workers employed less than 3 months, and 3 to 6 months, had significantly raised rates of respiratory cancer and pleural mesothelioma. Peritoneal mesothelioma appeared only in people employed a year or longer. The authors concluded the excesses were due to occupational asbestos exposure. They noted they could not control for smoking and that death certificates likely undercount asbestos disease.

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 (an update of a 1998 analysis) based on death certificates, comparing observed with expected deaths (standardized mortality ratios) using the CDC Life Table Analysis System
• Who was studied: 1130 former workers of the Tyler, Texas asbestos plant (1121 men, 9 women). 1039 had complete employment records. Deaths were followed through 2011, and 569 death certificates were included in the analysis.
• Exposure: Amosite asbestos used in manufacturing asbestos pipe insulation, 1954 to 1972. Length of employment was used as a stand-in for exposure.
• Main results:
  • Excess deaths were found for all causes, all cancers, cancers of the digestive organs and peritoneum, cancers of the respiratory system, and nonmalignant respiratory disease
  • Lung cancer (trachea, bronchus, lung): 89 deaths, SMR 244 (95% CI 196 to 300)
  • Intestinal cancer: SMR 240 (95% CI 146 to 370). All 20 deaths in this category were colon cancer, and there were no rectal cancer deaths.
  • Pneumoconiosis: 23 deaths observed vs 4.78 expected, SMR 481 (95% confidence limits 305 to 722)
  • Mesothelioma: 16 pleural and 7 peritoneal deaths, about 4% of all deaths
  • Short employment (less than 3 months, and 3 to less than 6 months) was associated with significantly elevated SMR for pleural mesothelioma and respiratory cancers
  • No peritoneal mesothelioma deaths occurred in workers employed less than 1 year. Median employment was 4.99 months for pleural mesothelioma deaths vs 33.75 months for peritoneal mesothelioma deaths, a significant difference.
  • Most mesothelioma deaths occurred 30 or more years after first exposure. Significant excesses of lung and all respiratory cancer appeared from 15 to 20 years after first exposure.
• The authors' conclusion: The authors concluded that the update confirms significant excess deaths from lung cancer, pleural and peritoneal mesothelioma, colon cancer (not rectal), and asbestosis, which they attributed to occupational asbestos exposure
• Limitations the authors state:
  • Death certificates may contain wrong or missing diagnoses, so asbestos-related illness is likely underestimated
  • Excluding workers with incomplete employment records likely introduced selection bias
  • Smoking could not be controlled for. Smoking data were missing in almost one-third of cases.
  • Limited data on other asbestos or respiratory exposures before or after work at the plant may bias toward excess cancer deaths
  • Death certificates for deaths outside Texas were not pursued, and people with unknown status were counted as alive
  • Employment duration was used as a proxy for exposure and assumes constant exposure levels
  • ICD-9 has no specific code for pleural or peritoneal mesothelioma, so these were coded as cancers of the pleura or peritoneum

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite, Asbestosis.

Medical terms in this study, explained in our Lexicon: Amosite, Pipe Covering, Death Certificate, Neoplasm, Mesothelioma, Bronchus, Lung Cancer, Pleural Mesothelioma.

Related studies

• Tyler asbestos workers: mortality experience in a cohort exposed to amosite — J.L. Levin, J.W. McLarty, et al. (1998)
• Human health effects associated with the commercial use of grunerite asbestos (amosite): Paterson, NJ; Tyler, TX; Uxbridge, UK — J. Ribak, G. Ribak (2008)
• Occupational carcinogenesis. High-risk industrial groups: identification, education, and surveillance. Tyler Asbestos Workers Program — S.D. Greenberg, G.A. Hurst, et al. (1976)
• Findings from high resolution computed tomography of the lung and pleura of symptom free workers exposed to amosite who had normal chest radiographs and pulmonary function tests — S. Neri, A. Antonelli, et al. (1994)
• Mortality Update of a Cohort of Canadian Petroleum Workers — A.R. Schnatter, N.C. Wojcik, et al. (2019)
• Rapporteur's Report Session 3: exposure to grunerite (amosite) asbestos: historical perspectives of the health effects — G.W. Gibbs (2008)

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