Refractory ceramic fiber (RCF) toxicity and epidemiology: A review

Abstract

This paper provides a review of the relevant literature on refractory ceramic fibers (RCFs), summarizing relevant data and information on the manufacture, processing, applications, potential occupational exposure, toxicology, epidemiology, risk analysis, and risk management. RCFs are amorphous fibers used for high-temperature insulation applications. RCFs are less durable/biopersistent than amphibole asbestos, but more durable/biopersistent than many other synthetic vitreous fibers (SVFs). Moreover, as produced/used, some RCFs are respirable. Toxicology studies with rodents using various exposure methods have shown that RCFs can cause fibrosis, lung cancer, and mesothelioma. Interpretation of these animal studies is difficult for various reasons (e.g., overload in chronic inhalation bioassays). Epidemiological studies of occupationally exposed cohorts in Europe and the United States have demonstrated measurable effects (e.g., mild respiratory symptoms and pleural plaques) but no disease (i.e., no interstitial fibrosis, no excess lung cancer, and no mesothelioma) to date. The RCF industry, working cooperatively with various government agencies in the United States, has developed a comprehensive product stewardship program (PSP) to identify and control risks associated with occupational exposure. One provision of the PSP is the adoption of a voluntary recommended exposure guideline (REG) of 0.5 fibers/milliliter (f/ml). Selected on the basis of prudence and demonstrated feasibility, compliance with the REG should reduce risks to levels between 0.073/1000 and 1.2/1000, based on extrapolations from chronic animal inhalation studies.

Are pleural plaques an appropriate endpoint for risk analyses?

“…The latency period for pleural plaques related to asbestos exposure is typically reported as 15-40 years (ACC Review, 2004;British Thoracic Society, 2011;Chapman et al, 2003;Hillerdal, 1981Hillerdal, , 1994Utell & Maxim, 2010). However, Larson et al (2010) reported a much reduced latency (median 8.6 years, range 1.4-14.7 years) for pleural plaques associated with exposure to LAA.…”

“…With very few exceptions (Cramond & Casserly, 2006;Hilt et al, 1987;Mukherjee et al, 2000;Myers, 2012) investigators have concluded that most subjects with pleural plaques are nearly always asymptomatic (Ameille & Letourneux, 1999;Broderick et al, 1992;Christen et al, 1997;Crane et al, 2005;Crapo, 2005;Dweik & Mazzone, 2010;Fishwick & Barber, 2014;Hillerdal, 1997Hillerdal, , 2001Hillerdal & Henderson, 1997;IIAC, 2008;Järvholm & Larsson, 1988;Jones, 1997;Meirelles et al, 2005;Mohr, 2012;Montes et al, 2005;Park et al, 2011;Roach et al, 2002;Rubin, 1986;Utell & Maxim, 2010). For example: Broderick et al (1992) studied an asbestos exposed population of sheet metal workers and examined the relationship between circumscribed plaque and four symptoms; dyspnea upon hurrying or walking up a slight hill (DOE), dyspnea worse than peers while walking (DSP), chest pain and cough.…”

Asbestos-Related Research: First Objectivity then Conclusions

“…Asbestos production and trade is prohibited in some countries, while others have maintained or increased production and use in recent years. Substitution of asbestos by artificial fibers would not necessarily lower or eliminate health risks [10][11][12][13]96,97]. The increased incidence of malignant Mt in developed nations [98,99], despite the prohibition of asbestos, is probably at least in part due to improved diagnostics, an increasing awareness of Mt, a screening effect in asbestos-exposed populations, and some over-diagnosis in conditions with an unclear demarcation of malignant Mt as an entity.…”

“…It can be spontaneous, or occur when asbestos fibers are present in the pulmonary or pleural tissues. Apart from asbestos, other potential etiologic factors of malignant Mt are mineral (erionite) and artificial (ceramic, carbone nanotubes) fibers [10][11][12][13], virus SV40, radiation, and genetic predisposition [14][15][16][17] (Figure 2). …”

Co-exposure to refractory ceramic fibres and asbestos and risk of pleural mesothelioma

“…From animal studies, it has been shown that inhalation of RCF produced fibrosis and pleural tumours [2]. However, the experiment protocols were criticised and it has been hypothesised that a lung overload effect occurred in these studies [3].…”