Exposures and mortality among chrysotile asbestos workers. Part I: exposure estimates

Our plain-English summary of Exposures and mortality among chrysotile asbestos workers. Part I: exposure estimates, by J.M. Dement, R.L. Harris, M.J. Symons, et al (American Journal of Industrial Medicine, 1983).

The study

• Authors: J.M. Dement, R.L. Harris, M.J. Symons, C.M. Shy
• Journal: American Journal of Industrial Medicine
• Published: 1983;4(3):399-419
• Cited by: 90 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. 005002).

Abstract

A detailed study of plant processes and dust control methods over the period 1930-1975 was conducted in an asbestos textile plant processing chrysotile. Linear statistical models for reconstructing historic dust exposure levels, taking into account textile processes, dust control measures, and job assignments, were developed. Parameters of these statistical models were estimated using 5,952 industrial hygiene sampling measurements covering the period 1930-1975. For most textile operations, exposure levels were significantly reduced by about 1940, when most engineering dust control measures were in place. Results of the exposure estimates indicated "precontrol" exposure levels to range from 3 to 78 fibers/cc with typical levels well above 10 fibers/cc. After textile operations were provided with dust control measures, estimated exposure levels ranged from 3 to 17 fibers/cc and were usually in the range of 5 to 10 fibers/cc. These exposure estimates were combined with an assessment of mortality among workers at this plant to investigate exposure-response relationships. Exposure-response results are presented in the companion manuscript in this volume.

In plain English

This paper was Part I of a study of workers at an asbestos textile plant that processed chrysotile. It described how the authors estimated workers' past dust exposures; deaths were analyzed in a companion paper. Chrysotile was the only asbestos processed there as raw fiber. From the 1950s to about 1975, a small amount of crocidolite yarn (under 2,000 pounds in all) was woven into tape, always wet, or braided into packing. The authors traced dust controls from 1930 to 1975 and built statistical models from 5,952 air samples, grouping jobs by plant area and task. They converted older particle-count samples to fiber counts using factors they described as likely to overestimate exposure. In most operations, estimated exposures fell by about 1940, when most dust controls were in place. Before controls, estimates ranged from about 3 to 78 fibers per cc and were typically well above 10. Afterward they ranged from about 3 to 17, usually 5 to 10. The authors concluded the estimates were within reasonable limits. They noted that some exposure misclassification was unavoidable.

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 exposure reconstruction (industrial hygiene records and statistical modelling) carried out for a retrospective cohort mortality study; mortality results are in a companion paper
• Who was studied: One asbestos textile plant processing chrysotile, studied over 1930-1975 using 5,952 industrial hygiene air samples gathered from the insurance carrier, the State Board of Health, the U.S. Public Health Service and the company. Workers' job histories came from plant personnel records.
• Exposure: Chrysotile (received from Quebec, British Columbia and Rhodesia), about 6-8 million pounds a year, in textile operations from fiber preparation and carding through spinning, twisting, winding and weaving. A small amount of crocidolite yarn (less than 2000 pounds in total) was woven into tape or made into braided packing from the 1950s to about 1975. All weaving of crocidolite tapes was done wet on a single loom, and crocidolite was never carded, spun or twisted. Exposure was measured as fibers longer than 5 micrometers per cc.
• Main results:
  • In most textile operations, estimated exposures were significantly reduced by about 1940, when most engineering dust controls were in place.
  • Before dust controls, estimated exposures ranged from about 3 to 78 fibers/cc and were typically well above 10 fibers/cc.
  • After controls were installed, estimated exposures ranged from approximately 3 to 17 fibers/cc and were usually 5 to 10 fibers/cc.
  • The highest estimate was for fly machine operators and crusher operators in fiber preparation in 1930-1944: 78.0 fibers longer than 5 micrometers per cc (95% confidence interval 38.1-117.8). For fly machine operators the estimate fell to 23.9 (17.7-30.2) in 1945-1964 and to 17.2 (13.1-21.3) in 1965-1975.
  • Twister operators had an estimated 36.0 fibers longer than 5 micrometers per cc (95% confidence interval 19.2-52.7) in 1930-1938, compared with 7.9 (6.7-9.2) in 1939-1975.
  • From paired samples, a mean of 2.9 fibers longer than 5 micrometers per cc was equivalent to one MPPCF (impinger particle-count unit). The study used conversion factors of 3, and 8 for fiber preparation.
  • The authors compared their estimates with a U.S. Public Health Service survey of other asbestos textile plants (Lynch and Ayer, 1966). The best-controlled plants in that survey had lower levels than this plant's post-control estimates. The authors wrote that the levels in the highest-exposure plants were approximated by this plant's pre-control estimates.
• The authors' conclusion: The authors concluded that the exposure estimates for this plant were well within reasonable limits and consistent with others' findings for textile operations. They considered that their models gave reasonable estimates without significant upward or downward bias.
• Limitations the authors state:
  • The authors stated that some exposure misclassification is unavoidable in a retrospective study. They expected it to affect diseased and non-diseased workers alike, which would tend to reduce any exposure-response gradients.
  • The authors stated that the factors used to convert particle counts to fiber counts were near the upper limits of their confidence intervals and may overestimate true fiber exposure levels.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Dust Control, Industrial Hygiene Sampling.

Related studies

• Exposures and mortality among chrysotile asbestos workers. Part II: mortality — J.M. Dement, R.L. Harris, et al. (1983)
• Estimates of historical exposures by phase contrast and transmission electron microscopy in North Carolina USA asbestos textile plants — J.M. Dement, D. Myers, et al. (2009)
• Increased lung cancer mortality among chrysotile asbestos textile workers is more strongly associated with exposure to long thin fibres — D. Loomis, J.M. Dement, et al. (2012)
• Estimates of historical exposures by phase contrast and transmission electron microscopy for pooled exposure--response analyses of North Carolina and South Carolina, USA asbestos textile cohorts — J.M. Dement, D. Loomis, et al. (2011)
• Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses — J.M. Dement, D.P. Brown, et al. (1994)
• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)

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