Pulmonary fibrosis in workers exposed to non-asbestiform tremolite asbestos minerals

Our plain-English summary of Pulmonary fibrosis in workers exposed to non-asbestiform tremolite asbestos minerals, by H.Y. Yang, R.H. Shie, P.C. Chen (Epidemiology, 2013).

The study

• Authors: H.Y. Yang, R.H. Shie, P.C. Chen
• Journal: Epidemiology
• Published: 2013;24(1):143-9
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Studies of the health effects of non-asbestiform asbestos minerals remain inconclusive. Nephrite is a type of non-asbestiform tremolite mineral. We assessed the risk for pulmonary fibrosis in workers who process nephrite.

Methods: A cross-sectional study that included 344 stone workers and their families was undertaken in Taiwan in 2010. The diagnostic criteria for pulmonary fibrosis included (1) radiographic fibrosis profusion of 1/1 or greater and (2) audible lung crackles confirmed by physician. The nephrite samples were analyzed using polarized light and transmission electron microscopy combined with selected-area electron diffraction and energy-dispersive x-ray spectroscopy.

Results: After excluding 16 subjects with histories of tuberculosis or previous employment in metal casting and welding, as well as 23 family members who had not worked in the stone industry, we analyzed 305 subjects. Processing nephrite increased the risk for pulmonary fibrosis (odds ratio = 2.8 [95% confidence interval = 1.0-9.9] and unchanged after adjustment for age and smoking). Bulk sample analyses showed that the nephrite is a tremolite mineral composed of both asbestiform and non-asbestiform components. The cat's-eye nephrite had the highest asbestiform fibrous content, and the average length and aspect ratio of elongated mineral particles were the highest of all the nephrite types. Compared with workers processing other types of nephrite, workers processing cat's-eye nephrite had the highest risk for pulmonary fibrosis.

Conclusion: Processing non-asbestiform tremolite mineral may increase the risk for pulmonary fibrosis. Medical monitoring is warranted for workers with such exposure.

In plain English

This cross-sectional study of stone workers in Hualien, Taiwan, compared those who processed nephrite (jade), described by the authors as non-asbestiform tremolite, with other stone workers. Of 1902 stone union members invited, 344 enrolled. After exclusions, 305 workers were analyzed, 53 of whom processed nephrite. Pulmonary fibrosis was defined as a chest x-ray profusion of 1/1 or greater plus physician-confirmed lung crackles. Nephrite workers had a crude odds ratio of 2.8 (95% confidence interval 1.0 to 7.9). Adjusted for age and smoking, it was 2.9 (0.9 to 9.2), a range including 1. Adjusted odds ratios were 3.4 (1.2 to 9.9) for dark green, 4.0 (1.2 to 13.9) for waxy and 6.3 (2.1 to 18.7) for cat's-eye nephrite. Microscopy found cleavage fragments and asbestiform fibers in nephrite samples, and cat's-eye nephrite had the highest share of asbestiform fibers. The authors concluded that processing non-asbestiform tremolite may increase the risk of pulmonary fibrosis and that medical monitoring is warranted. They noted the cross-sectional design's limited value for showing timing, and that recall bias and mixed stone-dust exposure could not be ruled out.

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: cross-sectional study, with mineral analysis of nephrite bulk samples
• Who was studied: Stone workers in Hualien, Taiwan. 1902 stone union members were invited by mail and 344 enrolled. The study ran 2008 to 2010, with interviews from September 2009 to September 2010. The authors excluded 16 people with tuberculosis or more than 10 years of metal casting or welding, and 23 family members who had never worked in the stone industry. That left 305 workers for analysis, 53 of whom processed nephrite (Table 1); workers exposed to a specific stone were compared with all other stone workers.
• Exposure: Processing nephrite (jade), described by the authors as non-asbestiform tremolite: dark green, waxy and cat's-eye types. Exposure was assessed by questionnaire on frequency, duration and wet or dry processing, checked against labor insurance records. Workers handling other stones (chalcedony, granite, marble, calcite) were also analyzed.
• Main results:
  • Among all 305 workers, 64 (21%) had x-ray fibrosis profusion of 1/1 or greater and 17 (6%) had lung crackles.
  • Among all 305 workers, nine (3%) had pleural plaques or thickening, and there was one lung cancer.
  • For workers who processed nephrite, compared with other stone workers, the crude odds ratio for pulmonary fibrosis was 2.8 (95% CI 1.0 to 7.9). After adjustment for age and pack-years of smoking it was 2.9 (0.9 to 9.2).
  • Adjusted odds ratios for pulmonary fibrosis by nephrite type were: dark green 3.4 (1.2 to 9.9), waxy 4.0 (1.2 to 13.9), and cat's-eye 6.3 (2.1 to 18.7).
  • When results were split by cumulative years of exposure, risks were increased for workers processing dark green and cat's-eye nephrite, independent of age and smoking.
  • In a Cox model using work-history timing, the adjusted hazard ratio for workers processing cat's-eye nephrite was 2.8 (95% CI 1.0 to 7.7).
  • Polarized light microscopy showed the nephrite samples were composed of microcrystalline asbestiform tremolite-actinolite minerals.
  • By transmission electron microscopy, the ratio of cleavage fragments to intact asbestiform fibers was 90:10 for dark green nephrite, 60:40 for waxy nephrite and 50:50 for cat's-eye nephrite.
  • Mean length-to-width (aspect) ratios of elongated mineral particles were 11:1 for dark green, 14:1 for cat's-eye and 12:1 for waxy nephrite.
• The authors' conclusion: The authors concluded that workers who processed non-asbestiform tremolite mineral had an increased risk of pulmonary fibrosis and that medical monitoring is warranted for workers with similar exposures.
• Limitations the authors state:
  • As a cross-sectional study, it has limited value for showing that exposure came before disease.
  • Recall bias could not be ruled out.
  • The observed risks might have come from exposure to other stones, since some workers used several types.
  • Comparing digital chest x-rays with lower-resolution digitized standard films may have increased how often x-ray fibrosis was found.

Topics

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

Medical terms in this study, explained in our Lexicon: Pulmonary Fibrosis, Non-Asbestiform, Tremolite, Asbestos, Fibrosis, Transmission Electron Microscopy (TEM), Odds Ratio, confidence interval.

Related studies

• Carving of non-asbestiform tremolite and the risk of lung cancer: a follow-up mortality study in a historical nephrite processing cohort — H.Y. Yang, R.H. Shie, et al. (2013)
• Mineralogical and exposure determinants of pulmonary fibrosis among Québec chrysotile miners and millers — A. Nayebzadeh, B.W. Case, et al. (2006)
• Lung mineral fibers of former miners and millers from Thetford-Mines and asbestos regions: a comparative study of fiber concentration and dimension — A. Nayebzadeh, A. Dufresne, et al. (2001)
• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part I. Exposure estimates — H.E. Amandus, R. Wheeler, et al. (1987)
• Differential responses of murine alveolar macrophages to elongate mineral particles of asbestiform and non-asbestiform varieties: Cytotoxicity, cytokine secretion and transcriptional changes — T.O. Khaliullin, E.R. Kisin, et al. (2020)
• Dimensions of elongated mineral particles: a study of more than 570 fibers from more than 90 cases with implications for pathogenicity and classification as asbestiform vs. cleavage fragments — V.L. Roggli, C.L. Green (2019)

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