Biopersistence of refractory ceramic fiber in human lung tissue and a 20-year follow-up of radiographic pleural changes in workers

Our plain-English summary of Biopersistence of refractory ceramic fiber in human lung tissue and a 20-year follow-up of radiographic pleural changes in workers, by J.E. Lockey, V.L. Roggli, T.J. Hilbert, et al (Journal of Occupational and Environmental Medicine, 2012).

The study

• Authors: J.E. Lockey, V.L. Roggli, T.J. Hilbert, C.H. Rice, L.S. Levin, E.K. Borton, P.W. Biddinger, G.K. Lemasters
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2012;54(7):781-8
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: The biopersistence of refractory ceramic fiber (RCF) in human lung tissue is unknown and may contribute to an association between cumulative fiber exposure and radiographic changes.

Methods: Lung tissue fiber was analyzed for a case series of 10 RCF workers and a 20-year longitudinal chest radiograph study of 1323 workers was conducted.

Results: Within lung tissue, RCF comprised 14% to 100% of fibers 5 μm or more in length and was identified up to 20 years after RCF employment. Among workers with no reported asbestos exposure, cumulative exposure of more than 63 to 110 and more than 110 fiber-months/cm was associated with radiographic pleural changes of 8.5% (odds ratio, 7.2; 95% confidence interval, 1.4 to 36.8) and 11.6% (odds ratio, 10.3; 95% confidence interval, 2.1 to 49.9), respectively.

Conclusions: Refractory ceramic fiber can persist in human lung tissue for up to 20 years and may contribute to the significant association between cumulative fiber exposure and radiographic pleural changes.

In plain English

The authors studied workers in the refractory ceramic fiber (RCF) manufacturing industry in two parts. First, lung tissue was collected from 10 workers; seven had adequate tissue, giving 12 lung sections. In these lungs, 14% to 100% of fibers 5 μm or longer were consistent with RCF, and RCF was found in three workers 13 to 20 years after their last exposure. Talc and amphibole fibers were also found. No RCF was found in pleural tissue from two cases. Second, 20 years of chest X-rays were read for 1,323 workers. Among the 694 with no reported asbestos exposure, pleural changes were found in 8.5% of those with more than 63 to 110 fiber-months per cubic centimeter of cumulative exposure (odds ratio 7.2; 95% confidence interval 1.4 to 36.8) and 11.6% of those with more than 110 (odds ratio 10.3; 2.1 to 49.9), compared with 1.3% (2 of 159) in the lowest group, more than 0 to 7. No association was found with interstitial changes, though the authors noted low statistical power. The authors concluded that RCF can persist in the human lung and may contribute to the link with pleural changes.

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: Case series of lung tissue fiber analysis combined with a 20-year longitudinal chest radiograph study of a worker cohort
• Who was studied: 1323 workers (1115 men, 208 women) in production and nonproduction jobs at five RCF manufacturing sites, who provided 5768 chest radiographs from 1987 through 2008; 694 had no reported asbestos exposure. Lung tissue came from 10 workers, of whom 7 (all male, aged 35 to 84) had adequate tissue.
• Exposure: Refractory ceramic fiber (RCF), measured as duration and latency of RCF production employment and as cumulative fiber exposure in fiber-months per cubic centimeter. Cumulative exposure covered all jobs, not only production jobs.
• Main results:
  • Fiber counts came from 12 lung sections from the seven workers with adequate tissue.
  • In the seven workers' lung tissue, 14% to 100% of fibers 5 μm or more in length were consistent with RCF.
  • RCF was found in the lung tissue of three workers 13 to 20 years after their last exposure.
  • Across all seven cases, the most common fibers 5 μm or more were RCF (38%), talc (18%) and amphiboles (16%, including tremolite, amosite, anthophyllite and actinolite).
  • No RCF was found in the pleural tissue analyzed from two cases.
  • Among workers with no reported asbestos exposure, pleural changes were found in 8.5% of those with more than 63 to 110 fiber-months per cubic centimeter (odds ratio 7.2; 95% confidence interval 1.4 to 36.8) and in 11.6% of those with more than 110 (odds ratio 10.3; 95% confidence interval 2.1 to 49.9). These odds ratios are compared with the more than 0 to 7 fiber-months per cubic centimeter group.
  • The comparison (reference) group was workers with more than 0 to 7 fiber-months per cubic centimeter. In the no-asbestos group, 2 of these 159 workers (1.3%) had pleural changes (Table 3).
  • In the two highest cumulative exposure groups, the statistically significant odds ratios ranged from 3.3 to 5.7 for all 1323 subjects (adjusted for asbestos exposure) and from 7.2 to 10.3 for the group with no reported asbestos exposure.
  • In the group with no reported asbestos exposure, the odds ratio for pleural changes was 10.4 for more than 20 years' production duration, and 10.8 (95% confidence interval 2.4 to 47.9) for more than 20 years' latency.
  • Of the 61 workers with pleural changes, 51 had localized pleural thickening, eight had diffuse pleural thickening, and two had findings split between the two.
  • No exposure measure was associated with interstitial changes on chest X-ray, at either profusion 1/0 or higher or 0/1 or higher.
• The authors' conclusion: The authors concluded that RCF can persist in the human lung, and that this may contribute to an association between cumulative RCF exposure and pleural changes on chest X-rays.
• Limitations the authors state:
  • The tissue data set was too limited to derive meaningful associations between lung fiber concentrations and cumulative exposure.
  • The pleural tissue analyzed was too limited to evaluate the fiber burden in the human pleura.
  • The interstitial findings should be read with caution because study power was low; the study could only detect a fourfold effect.
  • The study did not have the data to calculate fiber half-times in the lung.

Topics

Medical terms in this study, explained in our Lexicon: biopersistence, Chest X-Ray, Asbestos Exposure, Cumulative Exposure, Odds Ratio, confidence interval.

Related studies

• Refractory ceramic fiber exposure and pleural plaques — J. Lockey, G. Lemasters, et al. (1996)
• A 30-year mortality and respiratory morbidity study of refractory ceramic fiber workers — G. LeMasters, J.E. Lockey, et al. (2017)
• Potential significance of airborne fiber dimensions measured in the U.S. refractory ceramic fiber manufacturing industry — T.J. Lentz, C.H. Rice, et al. (1999)
• Risk analysis for mortality from respiratory tumors in a cohort of refractory ceramic fiber workers — A.M. Walker, L.D. Maxim, et al. (2002)
• Are airborne refractory ceramic fibers similar to asbestos in their carcinogenicity? — A.M. Walker, L.D. Maxim, et al. (2012)
• Low-level fiber-induced radiographic changes caused by Libby vermiculite: a 25-year follow-up study — A.M. Rohs, J.E. Lockey, et al. (2008)

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