Long term radiological effects of short term exposure to amosite asbestos among factory workers

Our plain-English summary of Long term radiological effects of short term exposure to amosite asbestos among factory workers, by R. Ehrlich, R. Lilis, E. Chan, et al (British Journal of Industrial Medicine, 1992).

The study

• Authors: R. Ehrlich, R. Lilis, E. Chan, W.J. Nicholson, I.J. Selikoff
• Journal: British Journal of Industrial Medicine
• Published: 1992;49(4):268-75
• Cited by: 41 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. 004127).

Abstract

Chest radiographs were read from a sub-cohort of 386 factory workers with short term exposure to amosite asbestos (median exposure six months) and long follow up (median 25 years). Prevalence of abnormality was determined independently by two readers from the first film available after 20 years from first employment. Serial films were obtainable for 238 men (median interval from first to last film: nine years). Progression was classified with a direct progression scoring scale. Individual dust exposure estimates were derived from dust counts from two similar plants. With as little as one month or less of employment, about 20% of the films showed parenchymal abnormality and about a third showed pleural abnormality. Those in the lowest cumulative exposure stratum (less than 5 fibre-years/ml) were similarly found to have high rates of abnormality. Dose-response relations were present in the data of both readers. Smokers had higher rates of parenchymal abnormality. On multivariate analysis, cumulative exposure was the exposure variable most closely related to parenchymal abnormality, and time from first employment was the variable most closely related to pleural abnormality. Progression (including first attacks) 20 or more years after ceasing employment occurred and was more common for pleural than for parenchymal abnormality. It is concluded that with exposure to high concentrations to amosite such as existed in this factory and with follow up for at least 20 years, (1) exposure for as little as a month was sufficient to produce radiological signs of parenchymal and pleural fibrosis, (2) no cumulative exposure threshold for parenchymal and pleural fibrosis was detectable, and (3) parenchymal and pleural progression were still detectable >/= 20 years after the end of exposure.

In plain English

This study examined chest x-rays of 386 men who started work at a Paterson, New Jersey, amosite asbestos insulation factory in 1941 to 1945. Many worked less than a year. Two certified readers independently read each man's first available film. For 22 men whose first film was taken under 20 years after starting work, they also read a later film. Serial films for 238 men were checked for progression. Exposure was estimated from dust counts at two similar plants. On films taken 20 or more years after starting work, 25% (reader 1) and 19% (reader 2) of men employed a month or less showed parenchymal (lung-tissue) abnormality, and 35% and 38% showed pleural abnormality. Parenchymal abnormality rose with cumulative exposure. Pleural abnormality was most closely linked to time since first employment. Progression, including newly appearing abnormality, was seen 20 or more years after employment ended, more often in the pleura. The authors concluded that as little as a month of exposure to high amosite concentrations was enough to produce radiological signs of fibrosis, with no detectable cumulative exposure threshold. They noted that unreported outside exposure and overreading could have raised the rates.

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: Cohort study of chest radiographs by two independent readers: prevalence of abnormality on films taken 20 or more years after first employment, plus side-by-side reading of serial films for progression
• Who was studied: 386 men (41% of the original cohort of 933 men who entered employment between June 1941 and December 1945) at an asbestos insulation plant in Paterson, New Jersey, who had chest films and no reported asbestos exposure in other jobs. 355 men had films taken 20 or more years after first employment, and 238 had serial films.
• Exposure: Almost entirely amosite from a single South African mine, with small amounts of chrysotile used at one time. Estimated fibre counts ranged from 5 fibres/ml (office workers) to 120 fibres/ml (disintegrator operators). Median duration of employment was 0.50 years and median cumulative exposure was 25.1 fibre-years/ml in the study group. The authors state that cumulative exposure also includes exposure at home.
• Main results:
  • On films taken 20 or more years after first employment, parenchymal abnormality was found in 25% (reader 1) and 19% (reader 2) of workers employed a month or less.
  • In the lowest cumulative exposure group (5 fibre-years/ml or less), the text reports parenchymal abnormality of 23% (reader 1) and 17% (reader 2). Prevalence increased with increasing cumulative exposure for both readers.
  • When a film counted as abnormal only if both readers read it as 1/0 or greater, rates were lower. The lowest duration and lowest cumulative exposure groups stayed above 10%, and the dose-response relation was preserved.
  • In logistic regression using each man's first film regardless of elapsed time, the odds ratio for parenchymal abnormality per 10 fibre-years/ml of cumulative exposure was 1.06 (95% CI 1.04 to 1.09) for reader 1 and 1.07 (95% CI 1.04 to 1.10) for reader 2.
  • On films taken 20 or more years after first employment, pleural abnormality was found in 35% (reader 1) and 38% (reader 2) of workers employed a month or less. No duration-response relation was detected for pleural abnormality.
  • Time from first employment was the variable most closely related to pleural abnormality. The odds ratio per decade was 1.67 (95% CI 1.15 to 2.42) for reader 1 and 1.85 (95% CI 1.24 to 2.76) for reader 2.
  • Smokers had higher rates of parenchymal abnormality than non-smokers, with an overall ratio of 1.34 for reader 1 and 1.25 for reader 2. After controlling for cumulative exposure, smoking showed no independent effect. Smoking showed no influence on pleural abnormality.
  • In serial films starting 20 or more years after last employment, parenchymal progression was seen in 44 cases (21%) by reader 1 and 29 cases (14%) by reader 2. Pleural progression was seen in 107 cases (50%) by reader 1 and 77 cases (36%) by reader 2. These counts include attacks, and the denominators were 212 and 211 readable serial sets.
• The authors' conclusion: The authors concluded that, with exposure to high concentrations of amosite as in this factory and follow-up of at least 20 years: exposure for as little as a month was sufficient to produce radiological signs of parenchymal and pleural fibrosis; no cumulative exposure threshold was detectable; and progression was still detectable 20 or more years after exposure ended.
• Limitations the authors state:
  • Some men may have had unreported or unknown asbestos exposure elsewhere, which would overestimate the rates attributable to this factory. The authors add that this could not account for the dose-response relations.
  • Overreading of films could explain some of the abnormality, especially at the low end of the ILO scale.
  • There was no unexposed group in this workforce.
  • Because surveillance mostly began 20 or more years after employment started, the authors could not tell when the changes first appeared.
  • The workers' cumulative exposure includes exposure at home from asbestos brought home on clothing.
  • No standardised method exists for reading progression, and direct progression scoring may give different results than random-order reading.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite, Asbestosis.

Medical terms in this study, explained in our Lexicon: Amosite, Chest X-Ray, Cumulative Exposure, Dose-response relationship, Multivariate Analysis, Fibrosis.

Related studies

• Mortality experience of amosite asbestos factory workers: dose-response relationships 5 to 40 years after onset of short-term work exposure — H. Seidman, I.J. Selikoff, et al. (1986)
• Spirometric impairments in long-term insulators. Relationships to duration of exposure, smoking, and radiographic abnormalities — A. Miller, R. Lilis, et al. (1994)
• Serum protein concentrations and respiratory tract abnormalities following short-term exposure to amosite: a comparison between former asbestos workers and unexposed controls — D.R. Nash, N.G. Fortson, et al. (1981)
• Quantification of the pathological response and fate in the lung and pleura of chrysotile in combination with fine particles compared to amosite-asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2011)
• The pathological response and fate in the lung and pleura of chrysotile in combination with fine particles compared to amosite asbestos following short-term inhalation exposure: interim results — D.M. Bernstein, R.A. Rogers, et al. (2010)
• Fiber levels and disease in workers from a factory predominantly using amosite — A.R. Gibbs, M.J. Gardner, et al. (1994)

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