A retrospective mortality cohort study of chrysotile asbestos products workers in Tianjin 1972-1987

Our plain-English summary of A retrospective mortality cohort study of chrysotile asbestos products workers in Tianjin 1972-1987, by W.N. Cheng, J. Kong (Environmental Research, 1992).

The study

• Authors: W.N. Cheng, J. Kong
• Journal: Environmental Research
• Published: 1992;59(1):271-8
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The mortality rate of a cohort of asbestos workers was investigated in Tianjin, China, between January 1, 1972, and December 31, 1987. The cohort consisted of 662 males and 510 females, employed in asbestos textiles, friction material, and asbestos cement manufacturing. A statistically significant excess mortality was observed for lung cancer in both males and females (SMR 278 and 427, respectively). An increasing trend in SMR was observed with increasing intervals of exposure as well as with increasing exposure level. A synergistic effect was seen between asbestos exposure and cigarette smoking regarding lung cancer. The ratio of smoking and nonsmoking lung cancer death rates was virtually the same in asbestos and in nonasbestos workers. This ratio was approximately 1.6, a value much less than that reported in other countries. This low ratio appears to reflect the fact that many nonsmokers were in fact passive cigarette smokers. Second, it reflects the fact that most smokers smoked hand-rolled tobacco, since manufactured cigarettes did not become popular in China until 1965. These data confirm the hazards of asbestos exposure in developing countries.

In plain English

This retrospective cohort study followed 1,172 workers (662 men and 510 women) at an asbestos products factory in Tianjin, China. The workers made asbestos textiles, friction material and asbestos cement, and the title describes them as chrysotile asbestos products workers. Those employed on January 1, 1972, with at least one year of exposure were followed for deaths through December 31, 1987. That covered 17,658.05 person-years, with 151 deaths and 44 cancer deaths. Lung cancer deaths were significantly higher than expected in men (SMR 278) and women (SMR 427). The excess rose with years of exposure, reaching an SMR of 667 at 30 or more years. It also rose with exposure level: no lung cancer deaths at low exposure against 1.07 expected, SMR 345 at middle and 396 at high. Workers 20 or more years from first exposure were compared with nonsmokers in a control group of 3,219 unexposed workers. Against that group, lung cancer death-rate ratios were 5.44 for exposed nonsmokers, 1.57 for unexposed smokers and 8.73 for exposed smokers. The authors concluded that asbestos acted synergistically with 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 mortality cohort study of one asbestos products factory, with follow-up from January 1, 1972 to December 31, 1987
• Who was studied: 1,172 workers (662 men, 510 women) employed at the Tianjin asbestos products factory on January 1, 1972 who had been exposed to asbestos for at least 1 year by then; followed to December 31, 1987
• Exposure: Asbestos (chrysotile according to the title) in textile work (carding, spinning, twisting), friction material and asbestos cement manufacturing. Dust was measured by weight in mg/m3, and concentrations fell after 1974 with equipment changes and exhaust ventilation. Workers were ranked into high, middle and low exposure levels by workshop and time worked, and cumulative dose was given in mg/m3-years.
• Main results:
  • Across the cohort there were 17,658.05 person-years, 151 deaths from all causes (116 men, 35 women) and 44 cancer deaths (30 men, 14 women).
  • Lung cancer mortality was significantly higher than expected in both sexes: SMR 278 in males and 427 in females.
  • By time since first exposure, lung cancer deaths were: less than 20 years, 2 observed vs 0.48 expected (no SMR given); 20 to 34 years, 14 vs 4.50 (SMR 311, P less than 0.01); 35 or more years, 5 vs 1.68 (SMR 297, P less than 0.05). The risk after 35 years was lower than between 20 and 35 years.
  • By duration of exposure, lung cancer deaths were: 1 to 14 years, 5 observed vs 2.27 expected (SMR 220, not marked significant); 15 to 29 years, 11 vs 3.64 (SMR 302, P less than 0.01); 30 or more years, 5 vs 0.75 (SMR 667, P less than 0.01).
  • By exposure level, lung cancer deaths were: low, 0 observed vs 1.07 expected; middle, 8 vs 2.32 (SMR 345); high, 13 vs 3.28 (SMR 396). By cumulative dose: under 400 mg/m3-years, SMR 289 (10 vs 3.42); 400 to under 800, SMR 271 (6 vs 2.21); 800 and above, SMR 485 (5 vs 1.03). All SMRs were P less than 0.01.
  • Lung cancer occurred in 13 of 456 workers with asbestosis and 8 of 716 without. The odds ratio was 2.597 (95% confidence limits 1.07 to 6.32). Lung cancer SMRs were printed as 3.20 for workers with asbestosis (13 observed vs 4.07 expected) and 3.06 for those without (8 vs 2.61).
  • Lung cancer death rates were measured 20 or more years from first exposure, per 100,000 person-years, standardized for age and smoking. The comparison group was nonsmokers in a control group of 3,219 workers not exposed to asbestos or to dust, fumes or vapor (rate 38.27). Mortality ratios against that group were 5.44 for asbestos-exposed nonsmokers (208.23), 1.57 for control smokers (60.31) and 8.73 for asbestos-exposed smokers (334.24).
  • The ratio of smokers' to nonsmokers' lung cancer death rates was 1.57 in the control group and 1.6 in the asbestos-exposed group. The authors attributed this low ratio to passive smoking among nonsmokers and to low smoke intake from hand-rolled cigarettes.
• The authors' conclusion: The authors concluded that asbestos exposure had a strong effect on lung cancer mortality among these Chinese workers. They related lung cancer mortality to intensity of exposure, duration of exposure, time since first exposure and cumulative dust exposure, and found that asbestos played a synergistic role with cigarette smoking.

Topics

Medical terms in this study, explained in our Lexicon: Cohort Study, Chrysotile, Asbestos Textiles, Asbestos-Cement, Lung Cancer, Synergistic Effect, Asbestos Exposure.

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