Quantitative Risk Assessment of Durable Glass Fibers

Abstract

This article presents a quantitative risk assessment for the theoretical lifetime cancer risk from the manufacture and use of relatively durable synthetic glass fibers. More specifically, we estimate levels of exposure to respirable fibers or fiberlike structures of E-glass and C-glass that, assuming a working lifetime exposure, pose a theoretical lifetime cancer risk of not more than 1 per 100,000. For comparability with other risk assessments we define these levels as nonsignificant exposures. Nonsignificant exposure levels are estimated from (a) the Institute of Occupational Medicine (IOM) chronic rat inhalation bioassay of durable E-glass microfibers, and (b) the Research Consulting Company (RCC) chronic inhalation bioassay of durable refractory ceramic fibers (RCF). Best estimates of nonsignificant E-glass exposure exceed 0.05-0.13 fibers (or shards) per cubic centimeter (cm3) when calculated from the multistage nonthreshold model. Best estimates of nonsignificant C-glass exposure exceed 0.27-0.6 fibers/cm3. Estimates of nonsignificant exposure increase markedly for E- and C-glass when non-linear models are applied and rapidly exceed 1 fiber/cm3. Controlling durable fiber exposures to an 8-h time-weighted average of 0.05 fibers/cm3 will assure that the additional theoretical lifetime risk from working lifetime exposures to these durable fibers or shards is kept below the 1 per 100,000 level. Measured airborne exposures to respirable, durable glass fibers (or shards) in glass fiber manufacturing and fabrication operations were compared with the nonsignificant exposure estimates described. Sampling results for B-sized respirable E-glass fibers at facilities that manufacture or fabricate small-diameter continuous-filament products, from those that manufacture respirable E-glass shards from PERG (process to efficiently recycle glass), from milled fiber operations, and from respirable C-glass shards from Flakeglass operations indicate very low median exposures of 0, 0.0002, 0.007, 0.008, and 0.0025 fibers (or shards)/cm3, respectively using the NIOSH 7400 Method ("B" rules). Durable glass fiber exposures for various applications must be well characterized to ensure that they are kept below nonsignificant levels (e.g., 0.05 fibers/cm3) as defined in this risk assessment.

Man-made mineral fiber effects on the expression of anti-oncogenes P53 and P16 and oncogenes C-JUN and C-FOS in the lung tissue of Wistar rats

“…They found an increased risk of respiratory system cancer in cohorts of MMMFexposed workers (Baccarelli et al, 2006;Greim et al, 2014;Shannon et al, 2005;Stone et al, 2004;Utell and Maxim, 2010). MMMFs could penetrate the epithelial cells and enter the lung interstitium (Fayerweather et al, 2002), which could induce persistent inflammation and lead to pulmonary fibrosis and respiratory cancer (Bottin et al, 2003). Studies have also shown that MMMFs could induce cancer in various experimental animals (Andersen et al, 2002); in addition, some in vitro toxicity studies have found that MMMFs exert cytotoxic and carcinogenic effects (Cui et al, 2018a;Rapisarda et al, 2015;Shibata et al, 2007).…”