Refractory ceramic fibers: Fiber characteristics, potential health effects and clinical observations

Our plain-English summary of Refractory ceramic fibers: Fiber characteristics, potential health effects and clinical observations, by M.J. Utell, L.D. Maxim (Toxicology and Applied Pharmacology, 2018).

The study

• Authors: M.J. Utell, L.D. Maxim
• Journal: Toxicology and Applied Pharmacology
• Published: 2018;361:113-117
• Type of article: Review
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Refractory ceramic fibers (RCFs) are amorphous fibers that belong to a class of materials termed synthetic vitreous fibers (SVFs), also called man-made mineral fibers (MMMFs), which includes alkaline earth silicate wool, glass wool, rock (stone) wool, slag wool, and special-purpose glass fibers. RCFs are more durable and biopersistent than several other SVFs, although very much less biopersistent than either amosite or crocidolite asbestos. Chronic inhalation studies indicated that rats and hamsters exposed to RCF fibers developed fibrosis and tumors. Epidemiological studies at the University of Cincinnati funded by the Industry indicated that exposed workers; (1) exhibited symptoms (e.g., dyspnea) similar to those reported in other dust-exposed populations, (2) developed statistically, but not clinically, significant deficits in certain measures of pulmonary function in a cross sectional study, but no excessive decline in a longitudinal study, and (3) a dose related increase in pleural plaques, but no interstitial fibrosis. The 2003 mortality study indicated no incremental lung cancer and no cases of mesothelioma. RCF producers developed a comprehensive industry wide product stewardship program (PSP) beginning in the late 1980s. In conjunction with the PSP, there has been a progressive decrease in the TWA concentration of fibers by manufacturers and end-users. The research program has successfully produced more soluble fibers and undertaken efforts to develop larger diameter fibers. 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.

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In plain English

This article is a review. The authors summarized published research on refractory ceramic fibers (RCFs), which are man-made glassy fibers used as high-temperature furnace insulation and contain no asbestos. They also described an industry product stewardship program begun in the late 1980s. They reported that RCFs stay in the lung longer than several other man-made fibers but much less long than amosite or crocidolite asbestos. Laboratory animal studies had produced fibrosis and tumors. Industry monitoring from 1990 through 2016 showed falling fiber levels at manufacturers and customers. Citing a 2017 University of Cincinnati study of 1451 RCF workers, the authors reported pleural changes in 6.1% overall, reaching 21.4% in the highest cumulative exposure group, with no rise in interstitial changes. In an industry-sponsored cross-sectional study, workers showed statistically but not clinically significant deficits in certain lung-function measures; a later longitudinal study found no excessive decline. A 2003 mortality study found no excess lung cancer and no mesothelioma. The authors concluded that RCF exposure causes selected respiratory symptoms and pleural plaques, but studies had not shown interstitial fibrosis, excess lung cancer or mesothelioma.

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: Narrative review of published research on refractory ceramic fibers and of the industry product stewardship program (exposure monitoring and controls, morbidity studies, product research)
• Who was studied: Published studies of RCF-exposed workers, including a 2017 University of Cincinnati study (LeMasters et al.) of 1451 RCF workers at 5 US facilities, plus an industry exposure database of nearly 26,000 personal monitoring measurements from the United States and Europe
• Exposure: Refractory ceramic fibers: amorphous (vitreous) synthetic fibers made by melting alumina and silica, used mainly as industrial furnace lining; the authors state they do not contain asbestos. The industry's recommended exposure guideline was 0.5 fibers per cubic centimeter.
• Main results:
  • Based on biopersistence data from other studies, RCFs were more durable and biopersistent than several other synthetic vitreous fibers but very much less biopersistent than amosite or crocidolite asbestos
  • Studies of laboratory animals exposed to RCF resulted in fibrosis and tumors. IARC placed RCF in Group 2B (possibly carcinogenic to humans).
  • Industry exposure monitoring from 1990 through 2016 showed fiber concentrations at customer facilities and manufacturer plants decreased substantially. Except for customers in 1990, levels were below the 0.5 f/cc guideline. These figures do not account for respirator use.
  • In the LeMasters et al. (2017) study of RCF workers, the overall rate of pleural changes was 6.1% (n=89)
  • In LeMasters et al. (2017), pleural changes rose across exposure categories. In the highest cumulative exposure category they reached 21.4% for all subjects (adjusted odds ratio 6.9, 95% CI 3.6 to 13.4). For those with no potential asbestos exposure they reached 13.0% (OR 9.1, 95% CI 2.5 to 33.6).
  • An earlier report (Lockey et al., 2002) found pleural changes in 27 workers (2.7%). In the 2017 study, prevalence among workers hired after 1985 was similar to background, and interstitial changes were not elevated.
  • Industry-sponsored studies found statistically significant but not clinically significant deficits in some lung-function measures in a cross-sectional study, but no excessive decline in a later longitudinal study
  • The 2003 mortality study found no incremental lung cancer and no cases of mesothelioma. It found a statistically significant association with cancers of the urinary organs, which the authors called unexpected and possibly due to chance.
  • The 2017 update reported one unconfirmed mesothelioma, in an individual with prior occupational asbestos exposure
  • Alkaline earth silicate (AES) wools, developed as substitutes, were reported in other studies to have significantly lower biopersistence than RCFs. In one 2-year rat inhalation study, one AES wool (X607) was neither fibrogenic nor carcinogenic.
• The authors' conclusion: The authors concluded that RCF exposure causes selected respiratory symptoms and pleural plaques. They stated that epidemiological studies had so far failed to demonstrate progressive lung-function loss, interstitial fibrosis, excess lung cancer or mesothelioma. They also concluded that the stewardship program reduced exposures and may explain the virtual absence of plaques in later hires.
• Limitations the authors state:
  • Animal results are hard to apply to humans because the key inhalation study resulted in particle overload
  • The ongoing mortality study was left out of this paper pending analysis of the latest update
  • The biological significance of the urinary-organ cancer finding is uncertain
  • Reported fiber concentrations do not account for the protective effect of respirators

Topics

Medical terms in this study, explained in our Lexicon: Vitreous, Mineral Fiber, Silicate, Amosite, Crocidolite, Fibrosis, Dyspnea, Pleural Plaques.

Related studies

• 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 fiber (RCF) toxicity and epidemiology: a review — M.J. Utell, L.D. Maxim (2010)
• Perspectives on refractory ceramic fiber (RCF) carcinogenicity: comparisons with other fibers — H. Greim, M.J. Utell, et al. (2014)
• Are airborne refractory ceramic fibers similar to asbestos in their carcinogenicity? — A.M. Walker, L.D. Maxim, et al. (2012)
• Risk analysis for mortality from respiratory tumors in a cohort of refractory ceramic fiber workers — A.M. Walker, L.D. Maxim, et al. (2002)
• Refractory ceramic fiber exposure and pleural plaques — J. Lockey, G. Lemasters, et al. (1996)

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