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

Exposure to insulating materials and risk of coronary artery diseases: a cross-sectional study

Background

Although previous reports link exposure to insulating materials with an increased risk of mesothelioma and chronic respiratory diseases, studies evaluating their associations with the risk of coronary artery diseases (CAD) are lacking.

Aims

We aimed at evaluating the associations between exposure to insulating materials and the 10-year risk of CAD among insulators.

Methods

In this cross-sectional study, we recruited 643 adults (≥18 years), full-time insulators from the Local 110 Heat and Frost Insulators and Allied Workers Union in Edmonton, Alberta. We obtained demographic information, personal and family history, and job-exposure history, including experience (years) and types of exposure to insulating materials. Clinical profiling including Framingham risk scores (FRS) was assessed.

Results

Of all insulators, 89% were men (mean ± SD age: 47 ± 12 years), 27% had a parental history of cardiac diseases, and 22% had a comorbid chronic respiratory disease. In total, 53% reported exposure to asbestos, while 61, 82, and 94% reported exposure to ceramic fibers, fiberglass, and mineral fibers, respectively. In single-exposure multivariable regression models adjusted for experience, marital status, and body mass index (BMI), asbestos was found to be associated with higher FRS (β: 1.004; 95%CI: 0.003-2.00). The association remained consistent in multi-exposure models and a higher association was found between asbestos exposure and FRS among insulators with comorbid chronic respiratory disease.

Conclusion

Our study demonstrates that apart from cancer and chronic respiratory diseases, asbestos exposure may also have a cardiac effect, thus warranting the need for systematic surveillance to protect workers from the adverse effects of these materials.

Toxicological evaluation of polycrystalline wools in human lung cells

Aim: Polycrystalline wools (PCW) are included with Refractory ceramic fibers (RCF) in the alumino-silicates family of High Temperature Insulation Wools (HTIW). IARC includes PCW in the ceramic fibers group and considers them as possible human carcinogens (GROUP 2B). Since PCW toxicity is not yet clear, our aim was to evaluate their toxic and inflammatory effects and to compare them with the known RCF effects.Method: We exposed human bronchial (BEAS-2B) and alveolar (A549) cells to 2-100 µg/mL (2.4 × 10³-1.2 × 10⁵ fibers/mL; 2.51 × 10³-1.26 × 10⁵ fibers/cm² of PCW and 7.4 × 10³-3.7 × 10⁵ fibers/mL; 7.75 × 10³-3.87 × 10⁵ fibers/cm² of RCF) of the tested fibers to evaluate potential viability reduction, apoptosis, membrane damage, direct/oxidative DNA-damage, cytokine release.Results: In A549, PCW did not induce cytotoxicity and apoptosis but they induced significant dose-dependent DNA-damage, although lower than RCF; only RCF induced oxidative effects. PCW also induced an increase in IL-6 release at 100 µg/mL (1.2 × 10⁵ fibers/mL; 1.26 × 10⁵ fibers/cm²). In BEAS-2B, PCW did not induce cell-viability reduction RCF induced a dose-dependent cell-viability decrease. Both fibers show a dose-dependent increase of apoptosis. In BEAS-2B, PCW also induced dose-dependent DNA-damage, although lower than RCF, and slight oxidative effects similar to RCF. PCW also induced an increase of IL-6 release; RCF induced a decrease of IL-8. Summarizing, PCW induce direct-oxidative DNA-damage although to a lower extent than RCF observed by both mass-based and fiber number-based analysis.Conclusion: For the first time, the study shows the potential toxicity of PCW, usually considered safe, and suggests to perform further in vitro studies, also on other cell types, to confirm these findings.

Mortality of workers employed in refractory ceramic fiber manufacturing: An update

This study evaluates the possible association between refractory ceramic fibers (RCF) exposure and all causes of death. Current and former employees (n=1,119) hired from 1952-1999 at manufacturing facilities in New York (NY) state and Indiana were included. Work histories and quarterly plant-wide sampling from 1987-2015 provided cumulative fiber exposure (CFE) estimates. The full cohort was evaluated as well as individuals with lower and higher exposure, <45 and >45 fiber-months/cc. The Life-Table-Analysis-System was used for all standardized mortality estimates (SMR). Person-years at risk accumulated from start of employment until 12/31/2019 or date of death. There was no significant association with all causes, all cancers, or lung cancer in any group. In the higher exposed there was a significant elevation in both malignancies of the "urinary organs" (SMR=3.59, 95% CI 1.44, 7.40), and "bladder or other urinary site" (SMR=4.04, 95% CI 1.10, 10.36) which persisted in comparison to regional mortality rates from NY state and Niagara County. However, six of the nine workers with urinary cancers were known smokers. In the lower exposed there was a significant elevation in malignancies of the lymphatic and hematopoietic system (SMR=2.54, 95% CI 1.27, 4.55) and leukemia (SMR=4.21, 95% CI 1.69, 8.67). There was one pathologically unconfirmed mesothelioma death. A second employee currently living with a pathologically confirmed mesothelioma was identified, but the SMR was non-significant when both were included in the analyses. The association of these two mesothelioma cases with RCF exposure alone is unclear because of potential past exposure to asbestos.

Rounded atelectasis after exposure to refractory ceramic fibres (RCF)

Background

Refractory Ceramic fibres (RCF) are man-made mineral fibres used in high performance thermal insulation applications. Analogous to asbestos fibres, RCF are respirable, show a pleural drift and can persist in human lung tissue for more than 20 years after exposure. Pleural changes such as localised or diffuse pleural thickening as well as pleural calcification were reported.

Result

A 45 years old man worked in high performance thermal insulation applications using refractory ceramic fibres (RCF) for almost 20 years. During a occupational medical prophylaxis to ensure early diagnosis of disorders caused by inhalation of aluminium silicate fibres with X-ray including high-resolution computed tomography (HRCT), bilateral pleural thickening was shown and a pleural calcification next to a rounded atelectasis was detected. Asbestos exposure could be excluded. In pulmonary function test a restrictive lung pattern could be revealed. In work samples scanning electron microscopy (SEM) including energy dispersive X-ray analysis (EDX) classified used fibres as aluminium silicate fibres. X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) showed crystalline as well as amorphous fibres.

Conclusions

A comprehensive lung function analysis and in case of restrictive lung disorders additional CT scans are needed in RCF exposed workers in accordance to the guidelines for medical occupational examinations comparable to asbestos exposed workers.

Release of Nanoparticles in the Environment and Catalytic Converters Ageing

A Three-Way Catalyst (TWC) contains a cordierite ceramic monolith coated with a layer of Al₂O₃, Ce_xZr_1−xO₂ and platinoids mixture. Under standard operation, the platinoid concentration decreases, exposing the remaining washcoat structure. After that particle release stage, the sintering process follows where the crystalline Ce_xZr_1−xO₂ solution is broken and begins to separate into ZrO₂ and CeO₂ phases. ZrO₂ is released to the environment as micro and nanoparticles, while a small amount of CeO₂ generates a new Al_xCe_1−xO₂ composite. The main effect of Ce capture is the growth in the size of the polycrystal structure from 86.13 ± 16.58 nm to 225.35 ± 69.51 nm. Moreover, a transformation of cordierite to mullite was identified by XRD analysis. Raman spectra showed that the oxygen vacancies (Vö) concentration decreased as Ce_xZr_1−xO₂ phases separation occurred_. The SEM-EDS revealed the incorporation of new spurious elements and microfractures favouring the detachment of the TWC support structure. The release of ultrafine particles is a consequence of catalytic devices overusing. The emission of refractory micro to nanocrystals to the atmosphere may represent an emerging public health issue underlining the importance of implementing strict worldwide regulations on regular TWCs replacement.

Identification of refractory zirconia from catalytic converters in dust: An emerging pollutant in urban environments

Using catalytic converters is one of the most effective methods to control vehicle emissions. A washcoat of cerium oxide-zirconia (CeO₂-ZrO₂) has been used to enhance the performance of the catalytic converter device. To date, the prevalence of this material in the environment has not been assessed. In this study, we present evidence of the existence of inhalable zirconia in urban dust. Samples of the washcoat, exhaust pipe, topsoil, and road dust were analyzed by X-ray fluorescence, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL) spectroscopy, and thermally stimulated luminescence (TSL). The results showed a CeO₂-ZrO₂ phase separation after sintering. This causes the emission of ZrO₂, CeO₂, and CeZrO_x particles smaller than 1 μm, which can likely reach the alveolar macrophages in the lungs. The Ce-Zr content in road dust exceeds geogenic levels, and a significant correlation of 0.87 (p < 0.05) reflects a common anthropic source. Chronic exposure to such refractory particles may result in the development of non-occupational respiratory diseases. The inhalable crystalline compounds emitted by vehicles are a significant environmental health hazard, revealing the need for further investigation and assessment of zirconia levels generated by automobiles in urban areas worldwide.

Non-Malignant Respiratory Illnesses in Association with Occupational Exposure to Asbestos and Other Insulating Materials: Findings from the Alberta Insulator Cohort

Many insulating materials are used in construction, although few have been reported to cause non-malignant respiratory illnesses. We aimed to investigate associations between exposures to insulating materials and non-malignant respiratory illnesses in insulators. In this cross-sectional study, 990 insulators (45 ± 14 years) were screened from 2011-2017 in Alberta. All participants underwent pulmonary function tests and chest radiography. Demographics, work history, and history of chest infections were obtained through questionnaires. Chronic obstructive pulmonary disease (COPD) was diagnosed according to established guidelines. Associations between exposures and respiratory illnesses were assessed by modified Poisson regression. Of those screened, 875 (88%) were males. 457 (46%) participants reported having ≥ 1 chest infection in the past 3 years, while 156 (16%) were diagnosed with COPD. In multivariate models, all materials (asbestos, calcium silicate, carbon fibers, fiberglass, and refractory ceramic fibers) except aerogels and mineral fibers were associated with recurrent chest infections (prevalence ratio [PR] range: 1.18-1.42). Only asbestos was associated with COPD (PR: 1.44; 95% confidence interval [CI]: 1.01, 2.05). Therefore, occupational exposure to insulating materials was associated with non-malignant respiratory illnesses, specifically, recurrent chest infections and COPD. Longitudinal studies are urgently needed to assess the risk of exposure to these newly implemented insulation materials.

Reinforcement of Bonding Strength and Water Resistance of Soybean Meal-Based Adhesive via Construction of an Interactive Network from Biomass Residues

Soybean meal-based adhesives are attractive potential environmentally friendly replacements for formaldehyde-based adhesives. However, the low strength and poor water resistance of soybean meal-based adhesives limit their practical application. This study was conducted to develop a natural fiber-reinforced soybean meal-based adhesive with enhanced water resistance and bonding strength. Pulp fiber (PF), poplar wood fiber (WF), and bagasse fiber (BF) were added as fillers into the soybean meal-based adhesive to enhance its performance via hydrogen bonding between the PF and the soybean meal system. The enhanced adhesive exhibited a strong crosslinking structure characterized by multi-interfacial interactions wherein PF served as a bridging ligament and released residual stress into the crosslinking network. The crosslinked structure and improved interfacial interactions were confirmed by Fourier transform infrared (FTIR) spectrophotometry, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) measurements. Plywood bonded with 4 wt % PF-containing soybean meal-based adhesive exhibited a wet shear strength (1.14 MPa) exceeding that of plywood bonded with the control group by 75.4% due to the stable crosslinking network having efficiently transformed stress and prevented the permeation of water molecules.