Review of refractory ceramic fiber (RCF) toxicity, epidemiology and occupational exposure

Our plain-English summary of Review of refractory ceramic fiber (RCF) toxicity, epidemiology and occupational exposure, by L.D. Maxim, M.J. Utell (Inhalation Toxicology, 2018).

The study

• Authors: L.D. Maxim, M.J. Utell
• Journal: Inhalation Toxicology
• Published: 2018;30(2):49-71
• Type of article: Review
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This literature review on refractory ceramic fibers (RCF) summarizes relevant information on manufacturing, processing, applications, occupational exposure, toxicology and epidemiology studies. Rodent toxicology studies conducted in the 1980s showed that RCF caused fibrosis, lung cancer and mesothelioma. Interpretation of these studies was difficult for various reasons (e.g. overload in chronic inhalation bioassays), but spurred the development of a comprehensive product stewardship program under EPA and later OSHA oversight. Epidemiology studies (both morbidity and mortality) were undertaken to learn more about possible health effects resulting from occupational exposure. No chronic animal bioassay studies on RCF have been conducted since the 1980s. The results of the ongoing epidemiology studies confirm that occupational exposure to RCF is associated with the development of pleural plaques and minor decrements in lung function, but no interstitial fibrosis or incremental lung cancer. Evidence supporting a finding that urinary tumors are associated with RCF exposure remains, but is weaker. One reported, but unconfirmed, mesothelioma was found in an individual with prior occupational asbestos exposure. An elevated SMR for leukemia was found, but was absent in the highly exposed group and has not been observed in studies of other mineral fibers. The industry will continue the product stewardship program including the mortality study.

In plain English

This article is a literature review, not a new study. The authors reviewed published work on refractory ceramic fibers (RCF), a type of synthetic vitreous fiber, focusing on developments since 2010. Much of it concerns the University of Cincinnati study of 1119 workers at two RCF plants in New York and Indiana (LeMasters et al., 2017). In that study, lung cancer deaths were not elevated in the full cohort (23 deaths, SMR 0.83, 95% CI 0.53–1.25). Urinary cancer deaths were elevated in the most exposed group of 285 workers (6 deaths, SMR 3.62, 95% CI 1.33–7.88). Leukemia deaths were elevated in the full cohort (8 deaths, SMR 2.51, 95% CI 1.08–4.94). One reported but unconfirmed mesothelioma occurred in a worker who had self-reported asbestos exposure as a vehicle mechanic. Pleural changes reached 21.4% in the highest exposure category, and interstitial changes were not elevated. The authors concluded that present occupational RCF exposures are unlikely to result in material decrements in lung function, interstitial fibrosis, incremental lung cancer or mesothelioma in the exposed population, and that follow-up should continue. They noted that most other risk factors for kidney and bladder cancer were not controlled for in that study.

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: Literature review focused on developments since 2010, updating the authors' earlier 2010 review
• Who was studied: Published papers and reports on RCF, identified from the authors' own knowledge and from PubMed and Google Scholar searches. The main human study discussed is the University of Cincinnati cohort of 1119 workers with at least 1 year of RCF employment at two manufacturing plants, one in New York and one in Indiana.
• Exposure: Refractory ceramic fibers: amorphous synthetic vitreous fibers made from alumina and silica and used as high-temperature insulation
• Main results:
  • UC mortality study, full cohort of 1119 workers: 23 deaths from cancer of the trachea, bronchus and lung, SMR 0.83 (95% CI 0.53–1.25)
  • UC mortality study, cancers of the urinary organs: full cohort 8 deaths, SMR 1.80 (95% CI 0.78–3.55); most exposed group (more than 45 fiber-months/cc, 285 workers) 6 deaths, SMR 3.62 (95% CI 1.33–7.88)
  • UC mortality study, leukemia: full cohort 8 deaths, SMR 2.51 (95% CI 1.08–4.94); most exposed group 3 deaths, SMR 2.57 (95% CI 0.53–7.50), which was not a significant excess
  • UC cohort: one reported but unconfirmed mesothelioma death, in a worker with self-reported occupational asbestos exposure as a vehicle mechanic for 6.5 years
  • UC cohort: the overall rate of pleural changes was 6.1%, rising across exposure categories to 21.4% in the highest cumulative fiber exposure category; interstitial changes were not elevated
  • UC cohort: among workers with localized pleural thickening, percent predicted FVC and FEV1 differed from workers without it by less than 3%, judged clinically insignificant
  • UC cancer incidence questionnaire (1011 participants): 4 respiratory cancers against 9.9 expected (SIR 0.40) and 2 urinary cancers against 6.4 expected (SIR 0.31)
  • A French case-control study (Lacourt et al., 2014) reported a higher risk of pleural mesothelioma with co-exposure to asbestos and RCF than with asbestos alone; the review authors said this finding should be viewed with caution
  • A French case-control study (Gerazime et al., 2015) found RCF exposure not significantly associated with head and neck cancer (OR 0.83; 95% CI 0.64–1.10) or lung cancer (OR 0.91; 95% CI 0.72–1.16); its authors said a moderate increase in risk could not be excluded
  • Industry monitoring data: weighted average exposures at US RCF manufacturing plants and customer facilities fell substantially from 1990 to 2016 and are now substantially below the US industry guideline of 0.5 f/ml
• The authors' conclusion: The authors concluded that epidemiology studies continue to support the view that present RCF occupational exposures are unlikely to result in material decrements in lung function, interstitial fibrosis, incremental lung cancer or mesothelioma in the exposed population. They considered the elevated leukemia SMR probably unrelated to RCF exposure, and the unconfirmed mesothelioma probably the result of prior asbestos exposure. They called for continued follow-up for kidney and bladder disease, leukemia and mesothelioma.
• Limitations the authors state:
  • Most known risk factors for kidney and bladder cancer (such as smoking, obesity, drugs and other occupational exposures) were not controlled for in the UC study
  • About half of the UC cohort had self-reported prior asbestos exposure, and the authors note that prior asbestos exposure is a general difficulty in epidemiological studies of fibers
  • The animal bioassays are hard to interpret because of possible lung overload, and risk estimates drawn from them span a wide range

Topics

Medical terms in this study, explained in our Lexicon: Epidemiology, Occupational Exposure, Fibrosis, Lung Cancer, Mesothelioma, OSHA, Pleural Plaques, Interstitial Fibrosis.

Related studies

• Refractory ceramic fiber (RCF) toxicity and epidemiology: a review — M.J. Utell, L.D. Maxim (2010)
• Are airborne refractory ceramic fibers similar to asbestos in their carcinogenicity? — A.M. Walker, L.D. Maxim, et al. (2012)
• 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)
• Refractory ceramic fibers: Fiber characteristics, potential health effects and clinical observations — M.J. Utell, L.D. Maxim (2018)
• Perspectives on refractory ceramic fiber (RCF) carcinogenicity: comparisons with other fibers — H. Greim, M.J. Utell, et al. (2014)
• Risk analysis for mortality from respiratory tumors in a cohort of refractory ceramic fiber workers — A.M. Walker, L.D. Maxim, et al. (2002)

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