Dust exposure and mortality in an American chrysotile asbestos friction products plant

Our plain-English summary of Dust exposure and mortality in an American chrysotile asbestos friction products plant, by A.D. McDonald, J.S. Fry, A.J. Woolley, et al (British Journal of Industrial Medicine, 1984).

The study

• Authors: A.D. McDonald, J.S. Fry, A.J. Woolley, J.C. McDonald
• Journal: British Journal of Industrial Medicine
• Published: 1984;41(2):151-7
• Cited by: 140 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000556).

Abstract

Cohort studies in three American asbestos factories were undertaken to investigate the effect of fibre type and manufacturing process on lung cancer, mesothelioma, and asbestosis. Reports have been published on a chrysotile textile plant in South Carolina and a mainly textile plant in Pennsylvania, which also used amphiboles. In the third plant in Connecticut friction products and packings were made from chrysotile only. In a cohort of 3641 men employed for one month or more, 1938-58, 3513 (96.5%) were traced, 1267 (36%) had died, and death certificates were obtained for 1228 (96.9%). Individual exposures were estimated (in mcpf . years) from impinger measurements. Life table analyses using Connecticut mortality rates gave an SMR for all causes of 108.5 (USA 107.9). The SMR (all causes) for men who had worked for less than a year was 129.9 and for those who had worked for a year or more, 101.2. The equivalent SMRs for respiratory cancer were 167.4 and 136.7 respectively. Excluding men who had worked for less than a year, there was possible evidence of some increase in risk of lung cancer with increasing exposure, supported also by a "log-rank" (case-control) analysis, of the same order as that observed in chrysotile mining and milling. These findings may be compared with chrysotile textile manufacture where the risk of lung cancer was some 50-fold greater. It is suggested that the differences in risk are perhaps related to the higher proportion of submicroscopic fibres in textile manufacture that may result from the traumatic carding , spinning, and weaving processes. No case of mesothelioma was found, consistent with a much lower risk of this tumour with chrysotile than with amphiboles. Twelve deaths (nine in men with very short and low asbestos exposure) were given ICD code 523 (pneumoconiosis); all but two were ascribed to anthracosilicosis or silicosis and none to asbestosis.

In plain English

This cohort mortality study followed men who worked at least a calendar month before 1959 at a Connecticut friction products and packings plant. It was the last of three American asbestos factory studies by the authors. Chrysotile was the only asbestos used until 1957, when some anthophyllite was added. Of 3641 men, 3513 were traced to the end of 1977, and 1267 had died. Dust exposure was estimated by department from particle-count measurements. Counting deaths 20 or more years after first employment (803 deaths), the standardised mortality ratio (SMR, where 100 means deaths as expected) for all causes was 108.5 using Connecticut rates. The excess came mainly from men employed under a year (SMR 129.9). Men employed a year or more had an SMR of 101.2. Respiratory cancer showed no clear rise with dust exposure. An increasing risk appeared only if the lowest-exposure group was ignored. No death certificate mentioned mesothelioma. None of the 12 deaths coded as pneumoconiosis mentioned asbestosis. The authors concluded that, if the excess among short-term workers reflected selection, the plant's adverse health effects 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 cohort mortality study. It used a man-years life table analysis against Connecticut (and United States) death rates and an internal case-control (Mantel-Haenszel log-rank) analysis.
• Who was studied: 3641 men employed for a calendar month or more before 1 January 1959 at a chrysotile friction products and packings plant in Connecticut, USA. Workers recorded in the woven brake lining parent plant's departments were excluded, as were women. Vital status was followed to 31 December 1977: 3513 (96.5%) were traced, 1267 (36%) had died, and death certificates were obtained for 1228 (96.9%).
• Exposure: Chrysotile asbestos, mainly from Canada, used in making friction materials (brake linings, clutch facings, transmission materials) and packings. It was the only asbestos type until 1957, when some anthophyllite was added for paper discs and bands. About 400 lb of crocidolite was handled experimentally in the laboratory between 1964 and 1972. Exposure was estimated by department and period from impinger measurements in million particles per cubic foot (mpcf), accumulated as mpcf-years, and was not converted to fibre counts. The average dust concentration for the men was 1.84 mpcf.
• Main results:
  • All causes, whole male cohort, counting deaths 20 years or more after first employment (803 deaths): SMR 108.5 using Connecticut rates (107.9 using United States rates).
  • All causes, by length of employment, counting deaths 20 years or more after first employment: SMR 129.9 for men who worked less than a year, and 101.2 for men who worked a year or more.
  • Respiratory cancer by accumulated dust exposure, counting deaths 20 years or more after first employment: SMR 125.8 for the two highest dust groups combined and 103.3 for the two intermediate groups combined. Both were below the SMR of 167.4 for the lowest exposure group (under 10 mpcf-years).
  • Respiratory cancer among men employed less than one year, all in the lowest dust category (under 10 mpcf-years), counting deaths 20 years or more after first employment: 24 deaths, SMR 180.0.
  • The Mantel-Haenszel analysis showed an increasing risk of respiratory cancer with dust exposure only if the minimal exposure group was ignored. Relative risks were 1, 0.40, 0.91, 1.40 and 1.13 across the five exposure groups.
  • No death certificate mentioned mesothelioma.
  • Twelve deaths were coded to pneumoconiosis (ICD 523). Six of these men had worked at the plant less than a year, and only three had a total dust exposure of 10 mpcf-years or more. Asbestosis was mentioned in none; anthracosilicosis or silicosis was given in all but two. All 12 had been born or had died in the coal mining area of Pennsylvania.
• The authors' conclusion: The authors concluded that, if the high mortality in men employed less than a year was due to some form of selection, the adverse health effects of working in this chrysotile friction products plant were small. They judged the respiratory cancer results closer to those of chrysotile mining and milling than to chrysotile textile manufacture. They also concluded that amphibole fibres are the main cause of mesothelioma, and that with chrysotile the risk of lung cancer varies greatly with industrial process. They suggested this variation may relate to finer, mainly submicroscopic fibres produced by more traumatic processes.
• Limitations the authors state:
  • Work histories rarely named the job or process, so exposure was estimated by department. The authors said this may have overestimated exposure for most employees in some departments and underestimated it for a few.
  • Particle counts were not converted to fibre measurements because of the work involved and the low confidence the authors could have placed in the results.
  • The excess deaths among short-term, low-exposure workers may reflect selective hiring of men in relatively poor health or with poor health habits (heavy smokers perhaps) into those jobs.
  • Short-term employees may have worked in other hazardous industries. The authors said this appeared to explain all or nearly all the pneumoconiosis deaths.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Friction Products, Lung Cancer, Mesothelioma, Amphibole Group, Death Certificate, Midget Impinger, Carding.

Related studies

• Dust exposure and mortality in an American chrysotile textile plant — A.D. McDonald, J.S. Fry, et al. (1983)
• Dust exposure and mortality in an American factory using chrysotile, amosite, and crocidolite in mainly textile manufacture — A.D. McDonald, J.S. Fry, et al. (1983)
• Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses — J.M. Dement, D.P. Brown, et al. (1994)
• Fibrous dust release from asbestos substitutes in friction products — S.A. Jaffrey, A.P. Rood, et al. (1992)
• Respiratory cancer in chrysotile textile and mining industries: exposure inferences from lung analysis — P. Sebastien, J.C. McDonald, et al. (1989)
• Increased risk of lung cancer mortality among residents near an asbestos product manufacturing plant — S. Kumagai, N. Kurumatani, et al. (2010)

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