Tyler asbestos workers: mortality experience in a cohort exposed to amosite

Our plain-English summary of Tyler asbestos workers: mortality experience in a cohort exposed to amosite, by J.L. Levin, J.W. McLarty, G.A. Hurst, et al (Occupational and Environmental Medicine, 1998).

The study

• Authors: J.L. Levin, J.W. McLarty, G.A. Hurst, A.N. Smith, A.L. Frank
• Journal: Occupational and Environmental Medicine
• Published: 1998;55(3):155-60
• Cited by: 42 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To examine the causes of death among 1130 former workers of a plant in Tyler, Texas dedicated to the manufacture of asbestos pipe insulation materials. This cohort is important and unusual because it used amosite as the only asbestiform mineral in the production process. High level exposure of such a specific type was documented through industrial hygiene surveys in the plant.

Methods: Deaths were ascertained through various sources including data tapes from the Texas Department of Health and the national death index files. As many death certificates as possible were secured (304/315) and cause of death assigned. After select exclusions, 222 death certificates were used in the analysis. Causes of death were compared with age, race, and sex specific mortalities for the United States population with a commercial software package (OCMAP Version 2.0).

Results: There was an excess of deaths from respiratory cancer including the bronchus, trachea, and lung (standardised mortality ratio (SMR) 277 with 95% confidence interval (95% CI) 193 to 385). Four pleural mesotheliomas and two peritoneal mesotheliomas were identified. The analysis also showed an increasing risk of respiratory malignancy with increased duration of exposure including a significant excess of total deaths from respiratory cancer with less than six months of work at the plant (SMR 268 with 95% CI 172 to 399).

Conclusions: The importance of the cohort lies with the pure amosite exposure which took place in the plant and the extended period of latency which has followed. The death certificate analysis indicates the pathogenicity of amosite, the predominant commercial amphibole used in the United States. These data confirm a link between amosite asbestos and respiratory malignancy as well as mesothelioma.

In plain English

This retrospective mortality study followed 1130 former workers of a plant in Tyler, Texas, that made asbestos pipe insulation from 1954 to 1972. The insulation was about 90% amosite. Plant surveys in 1967, 1970 and 1971 found average fiber concentrations of 15.9 to 91.4 fibres/ml. The analysis excluded women, non-white men, workers with missing dates, and deaths within 10 years of first employment, leaving 753 men among whom 222 deaths were recorded. Observed deaths were compared with the numbers expected from United States rates, as standardised mortality ratios (SMR, where 100 means as expected). Deaths from all causes (SMR 166, 95% CI 145 to 190) and from cancers of the bronchus, trachea and lung (35 observed versus 12.6 expected; SMR 277, 95% CI 193 to 385) were in excess. There were six mesothelioma deaths, four pleural and two peritoneal, and three asbestosis deaths. Men employed less than six months had excess respiratory cancer deaths (SMR 268, 95% CI 172 to 399). A trend test with longer employment was significant (p less than 0.05). The authors concluded the analysis indicates the pathogenicity of amosite. They noted they could not control for smoking.

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 based on United States rates (standardised mortality ratios)
• Who was studied: A cohort of 1130 former workers (1121 men, nine women) of an asbestos pipe insulation plant in Tyler, Texas, which operated from 1954 to February 1972. After excluding women, non-white men, workers with missing employment or birth dates, and deaths within 10 years of first employment, 753 workers (white men, including 72 men of unrecorded race assumed to be white) remained for analysis, with 222 deaths.
• Exposure: Amosite obtained from the Transvaal region of South Africa. The insulation was a mixture of about 90% amosite with diatomaceous earth, sodium silicate and mineral wool. Plant surveys in 1967, 1970 and 1971 found average fiber concentrations of 15.9 to 91.4 fibres/ml. Respirators were not mandatory until 1971. Duration of employment ranged from one day to 17.3 years (mean 12.7 months, median 1.6 months).
• Main results:
  • All causes of death in the analysis group: 222 observed versus 133.6 expected, SMR 166 (95% CI 145 to 190)
  • All malignant neoplasms in the analysis group: 78 observed versus 33.7 expected, SMR 231 (95% CI 183 to 289)
  • Cancer of the bronchus, trachea and lung in the analysis group: 35 observed versus 12.6 expected, SMR 277 (95% CI 193 to 385)
  • Six deaths from mesothelioma: four pleural and two peritoneal (about 3% of all deaths)
  • Non-malignant respiratory disease in the analysis group: 18 observed versus 8.3 expected, SMR 218 (95% CI 129 to 344). The 'other non-malignant respiratory disease' category included three deaths from asbestosis.
  • Malignant neoplasms of the digestive organs and peritoneum in the analysis group: 16 observed versus 8.1 expected, SMR 197 (95% CI 113 to 320)
  • Workers employed less than six months had a significant excess of respiratory cancer deaths: SMR 268 (95% CI 172 to 399)
  • The test for trend in respiratory cancer deaths with increasing duration of exposure was significant at p less than 0.05
• The authors' conclusion: The authors concluded that the death certificate analysis indicates the pathogenicity of amosite, which they describe as the predominant commercial amphibole used in the United States, and that the data confirm a link between amosite and respiratory malignancy as well as mesothelioma.
• Limitations the authors state:
  • Causes of death were taken from death certificates, and incomplete employment records could have introduced selection bias.
  • Smoking could not be controlled for because not all workers' smoking status was known.
  • Information on earlier and later exposures to asbestos and other agents was limited, so the excess of respiratory malignancy could be biased upward.
  • Workers of unknown vital status were assumed to be alive, which the authors say biases the SMRs downward by overestimating expected deaths.

Topics

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

Medical terms in this study, explained in our Lexicon: Amosite, Pipe Covering, Asbestiform, Industrial Hygiene, Death Certificate, Bronchus, confidence interval, Pleural Mesothelioma.

Related studies

• Tyler asbestos workers: A mortality update in a cohort exposed to amosite — J.L. Levin, A. Rouk, et al. (2016)
• Human health effects associated with the commercial use of grunerite asbestos (amosite): Paterson, NJ; Tyler, TX; Uxbridge, UK — J. Ribak, G. Ribak (2008)
• Cancer mortality in a cohort of asbestos textile workers — E. Pira, C. Pelucchi, et al. (2005)
• Historical cohort study of US man-made vitreous fiber production workers: II. Mortality from mesothelioma — G.M. Marsh, M.J. Gula, et al. (2001)
• Mortality experience of amosite asbestos factory workers: dose-response relationships 5 to 40 years after onset of short-term work exposure — H. Seidman, I.J. Selikoff, et al. (1986)
• 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)

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