Type of asbestos and respiratory cancer in the asbestos industry

Our plain-English summary of Type of asbestos and respiratory cancer in the asbestos industry, by P.E. Enterline, V. Henderson (Archives of Environmental Health, 1973).

The study

• Authors: P.E. Enterline, V. Henderson
• Journal: Archives of Environmental Health
• Published: 1973;27(5):312-7
• Cited by: 57 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001300).

In plain English

This study followed 1,348 men who retired from the asbestos industry between 1941 and 1967, counting deaths from age 65 through 1969. It compared them with the US white male population using standardized mortality ratios (SMRs), where 100 means the expected rate. Fiber type was taken from plant purchase records and products. Cumulative dust exposure was built from job histories and rough dust estimates. Overall, 58 respiratory cancer deaths were observed against 21.7 expected. Among 1,013 men exposed only to chrysotile, the SMR was 236.4 (237.7 after dust adjustment). Among 120 men exposed to chrysotile and crocidolite it was 526.3 (563.0 adjusted). In asbestos cement work, 7 of 156 deaths among 316 chrysotile-only shingle and sheet makers were respiratory cancer. This compared with 10 of 46 deaths among 106 pipe makers, whose pipe also contained crocidolite. The authors concluded that evidence of a relatively high cancer potential for crocidolite was particularly strong, and that chrysotile also has some carcinogenic or cocarcinogenic properties. They could not account for smoking for most men, and many groups were small.

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 retirees, with deaths compared against expected deaths based on the US white male population
• Who was studied: 1,348 men who retired from the asbestos industry from 1941 through 1967 (1,182 normal retirements, 87 early, 79 for disability), followed at ages 65 and over through 1969. Average employment was 25 years (range 3 to 51). A subgroup of 422 asbestos cement retirees was studied separately: 316 shingle and sheet makers and 106 pipe makers. Plant locations are not named.
• Exposure: Asbestos dust: chrysotile only, amosite only, or combinations of chrysotile with amosite and/or crocidolite. Fiber type was assigned from plant purchase records and finished products. Cumulative dust exposure was estimated in million particles per cubic foot times years (mppcf years). Cement shingles and sheets used only chrysotile; cement pipe used chrysotile plus crocidolite, the crocidolite making up 3% to 5% of the final product.
• Main results:
  • Whole cohort: 754 deaths were observed against 655.2 expected (SMR 115.1), an overall mortality 15.1% higher than all US men.
  • Whole cohort: 58 respiratory cancer deaths were observed against 21.7 expected (SMR 267.3).
  • Whole cohort: 18 deaths were due to asbestosis, and the excess in respiratory disease deaths was due entirely to pneumoconiosis and pulmonary fibrosis.
  • Respiratory cancer by fiber type. Chrysotile only (1,013 men): 39 deaths observed against 16.5 expected, SMR 236.4, dust-adjusted SMR 237.7. Chrysotile and crocidolite (120 men): 10 observed against 1.9 expected, SMR 526.3, adjusted SMR 563.0. The authors wrote that the respiratory cancer death rate in these two largest groups appeared to differ.
  • Amosite only (59 men from a single plant): 4 respiratory cancer deaths against 0.9 expected, SMR 444.4, adjusted SMR 390.7. The authors described this as a little high but based on very few deaths. For most fiber groups the numbers were too small to draw conclusions.
  • Summary rows. Any crocidolite (174 men): 12 observed against 2.8 expected, SMR 428.6, adjusted SMR 442.5. Any chrysotile (1,289 men): SMR 258.4, adjusted 260.0. Any amosite (215 men): SMR 264.7, adjusted 249.0. The authors wrote that this suggests crocidolite may be more carcinogenic.
  • Asbestos cement, all locations. Shingle and sheet makers (316 men, chrysotile only): 7 of 156 deaths were respiratory cancer, against 4.9 expected (SMR 142.9, adjusted 141.1). Pipe makers (106 men, chrysotile and crocidolite): 10 of 46 deaths were respiratory cancer, against 1.7 expected (SMR 588.2, adjusted 608.5).
  • At the three locations that made both cement products: shingle and sheet makers (153 men) had 3 respiratory cancer deaths against 2.4 expected (SMR 125.0, adjusted 119.2). Pipe makers (81 men) had 8 against 1.3 expected (SMR 615.4, adjusted 616.1).
  • When the 106 pipe retirees were roughly matched with 106 shingle and sheet retirees on year hired, age at hire and year of retirement, the difference in respiratory cancer SMRs was slightly larger than in Table 3.
  • Among the 1,013 chrysotile-only men the authors reported a clear dose-response relationship; no figures for it are given in this article.
• The authors' conclusion: The authors concluded that their data suggest that chrysotile may carry a relatively small risk compared with crocidolite, with amosite probably in between, as an earlier review by Wagner et al had proposed. They judged the evidence of a relatively high carcinogenic potential for crocidolite particularly strong because dose, geographic location and other occupational exposures could be controlled. They also wrote that there is little doubt chrysotile has some carcinogenic or cocarcinogenic properties, and that amosite data were less conclusive.
• Limitations the authors state:
  • Smoking could not be taken into account for most of the population. Smoking histories were available for only 56 of 316 shingle and sheet workers (82% smokers) and 26 of 106 pipe workers (81% smokers).
  • Dust levels, especially for past periods, could not be estimated precisely and were only roughly classified.
  • Where several products were made at one site, fibers could have been mixed between buildings or areas, and this could not be taken into account.
  • Death certificates were found for only 733 of the 754 deaths.
  • For most fiber types and combinations, the numbers were too small to draw conclusions.
  • The retirees were probably healthier than the US white male comparison population, mainly affecting cardiovascular deaths and probably much less so cancer.

Related studies

• Respiratory cancer in relation to occupational exposures among retired asbestos workers — P. Enterline, P. de Coufle, et al. (1973)
• Occupational respiratory cancer and exposure to asbestos: a case-control study in a cohort of workers in the electricity and gas industry — E. Imbernon, M. Goldberg, et al. (1995)
• Respiratory carcinogenesis: an epidemiologic appraisal — J.F. Fraumeni (1975)
• In vitro approaches for determining mechanisms of toxicity and carcinogenicity by asbestos in the gastrointestinal and respiratory tracts — B.T. Mossman (1983)
• Man-made vitreous fibers and risk of respiratory system cancer: a review of the epidemiologic evidence — I.M. Lee, C.H. Hennekens, et al. (1995)
• Environmental exposure to tremolite and respiratory cancer in New Caledonia: a case-control study — D. Luce, I. Bugel, et al. (2000)

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