Mortality of a cohort exposed to chrysotile asbestos

Our plain-English summary of Mortality of a cohort exposed to chrysotile asbestos, by W. Weiss (Journal of Occupational Medicine., 1977).

The study

• Author: W. Weiss
• Journal: Journal of Occupational Medicine.
• Published: 1977;19(11):737-40
• Cited by: 37 articles, as counted by NIH iCite
• Read it: PubMed
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001104).

Abstract

A 30-year historical cohort mortality study was made of 264 men hired during 1935-45 who worked in a chrysotile asbestos products factory for one year or more and were alive January 1, 1945. Follow-up was 94% complete. The overall standardized mortality ratio (SMR) was only 0.61 while the SMR for all cancers was 0.75, for lung cancer 0.93, and for gastrointestinal cancer 1.05. Two men died of asbestosis. The overall SMR was higher for men who worked five years or more than for men who worked one to four years but the 30-year mortality rates were the same after age adjustment. For asbestos-related diseases the differences in work duration had no effect on mortality. The data show a favorable mortality experience for men exposed to chrysotile alone.

In plain English

This was a historical cohort mortality study of 264 men first hired between 1935 and 1945 at a factory that had used only chrysotile asbestos since it opened in 1896. The men had worked there at least one year and were alive on January 1, 1945. Until 1960 the plant made chrysotile papers and millboard, and fiber could be seen in the air in most of the plant. Fiber counts were not measured until 1972. Deaths were traced to December 31, 1974. Vital status was known for 94% of the men, and 66 had died. Compared with U.S. white males, the overall standardized mortality ratio (SMR) was 0.61. SMRs were 0.75 for all cancers, 0.93 for lung cancer and 1.05 for gastrointestinal cancer. Two deaths from severe pulmonary fibrosis were counted as asbestosis. After age adjustment, men who worked five or more years had the same mortality rates as men who worked one to four years. No smoking information was available. The author concluded that the cohort's favorable experience suggests the hazard of chrysotile in asbestos products manufacturing is minimal.

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: Historical (retrospective) cohort mortality study with 30 years of follow-up, comparing observed deaths with deaths expected from U.S. white male mortality rates (standardized mortality ratios)
• Who was studied: 264 male production workers at a chrysotile asbestos products plant, first hired 1935-45, who worked at least one year and were alive on January 1, 1945. They were followed to December 31, 1974. The plant's location is not stated.
• Exposure: Chrysotile asbestos only. From 1935 to 1960 the plant made chrysotile papers and millboard (bound with starch or occasionally Portland cement) and aircell pipe insulation, with visible airborne fiber in most of the plant. Dust was much reduced after 1960. Fiber counts began only in 1972, and recent counts were reported as generally under 2 (the unit is garbled in the scan). Work duration was 1-4 years for 56% of men, 5-9 years for 16%, 10-19 years for 11% and 20 or more years for 17%.
• Main results:
  • Vital status was known for 94% of the cohort. There were 66 deaths, and death certificates were obtained for all but four.
  • For the whole cohort, the SMR for all causes was 0.61, for all cancers 0.75, for lung cancer 0.93 and for gastrointestinal cancer 1.05.
  • The all-causes SMR was 0.56 in the first 10-year period and 0.62 in the remaining two 10-year periods.
  • The SMR was higher for men who worked five or more years than for men who worked less than five years, but both groups' SMRs were statistically significantly lower than 1.00.
  • The 5+ year group's crude death rate was about 50% higher than that of the shorter-duration group. The author attributed this to age differences: after age adjustment the rates were the same.
  • Two deaths attributed to severe pulmonary fibrosis on death certificates were categorized as asbestosis. No SMR could be calculated for asbestosis.
  • Of ten deaths from diseases that might have been work-related, the author judged that asbestos could have been a factor in all four lung cancer deaths. Asbestos was judged unlikely as a cause in one gastric cancer death, and possibly in one colon cancer death, because of the short time since first exposure.
  • For asbestos-related diseases, differences in work duration had no effect on mortality.
• The authors' conclusion: The author concluded that the cohort's favorable mortality experience suggests the hazard of chrysotile in asbestos products manufacturing is minimal. The author considered this consistent with what is known of the relative dangers of chrysotile, amosite and crocidolite.
• Limitations the authors state:
  • No smoking information was available.
  • There were no quantitative exposure measurements for the high-dust years, and an exposure scale could not be built from the records.
  • Follow-up was 6% incomplete, and cause of death was missing for 6% of deaths. The author stated this would not change the conclusions.
  • Sixteen men with no Social Security information for some periods were assumed to be alive throughout follow-up.
  • Deaths for each cause were too few to give reliable ratios for each 10-year period.
  • It was unknown whether the men had asbestos exposure elsewhere, so total exposure duration was uncertain.

Topics

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

Related studies

• A retrospective mortality cohort study of chrysotile asbestos products workers in Tianjin 1972-1987 — W.N. Cheng, J. Kong (1992)
• A retrospective cohort study of cancer mortality in employees of a Russian chrysotile asbestos mine and mills: study rationale and key features — J. Schüz, S.J. Schonfeld, et al. (2013)
• Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses — J.M. Dement, D.P. Brown, et al. (1994)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992 — F.D. Liddell, A.D. McDonald, et al. (1997)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88 — J.C. McDonald, F.D. Liddell, et al. (1993)
• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)

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