A longitudinal study of chest radiographic changes of workers in the refractory ceramic fiber industry

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.

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

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.

Five years update on relationships between malignant pleural mesothelioma and exposure to asbestos and other elongated mineral particles

Despite the reduction of global asbestos consumption and production due to the ban or restriction of asbestos uses in more than 50 countries since the 1970s, malignant mesothelioma remains a disease of concern. Asbestos is still used, imported, and exported in several countries, and the number of mesothelioma deaths may be expected to increase in the next decades in these countries. Asbestos exposure is the main risk factor for malignant pleural mesothelioma, but other types of exposures are linked to the occurrence of this type of cancer. Although recent treatments improve the quality of life of patients with mesothelioma, malignant pleural mesothelioma remains an aggressive disease. Recent treatments have not resulted in appreciable improvement in survival, and thus development of more efficient therapies is urgently needed. The development of novel therapeutic strategies is dependent on our level of knowledge of the physiopathological and molecular changes that mesothelial cells acquired during the neoplastic process. During the past 5 years, new findings have been published on the etiology, epidemiology, molecular changes, and innovative treatments of malignant pleural mesothelioma. This review aims to update the findings of recent investigations on etiology, epidemiology, and molecular changes with a focus on (1) attributable risk of asbestos exposure in men and women and (2) coexposure to other minerals and other elongated mineral particles or high aspect ratio nanoparticles. Recent data obtained on genomic and gene alterations, pathways deregulations, and predisposing factors are summarized.

Perspectives on refractory ceramic fiber (RCF) carcinogenicity: comparisons with other fibers

In 2011, SCOEL classified RCF as a secondary genotoxic carcinogen and supported a practical threshold. Inflammation was considered the predominant manifestation of RCF toxicity. Intrapleural and intraperitoneal implantation induced mesotheliomas and sarcomas in laboratory animals. Chronic nose-only inhalation bioassays indicated that RCF exposure in rats increased the incidence of lung cancer and similar exposures resulted in mesothelioma in hamsters, but these studies may have been compromised by overload. Epidemiological studies in the US and Europe showed an association between exposure and prevalence of respiratory symptoms and pleural plaques, but no interstitial fibrosis, mesotheliomas, or increased numbers of lung tumors were observed. As the latency of asbestos induced mesotheliomas can be up to 50 years, the relationship between RCF exposure and respiratory malignances has not been fully determined. Nonetheless, it is possible to offer useful perspectives. RCF and rock wool have similar airborne fiber dimensions and biopersistence. Therefore, it is likely that these fibers have similar toxicology. Traditional rock wool has been the subject of numerous cohort and case control studies. For rock wool, IARC (2002) concluded that the epidemiological studies did not provide evidence of carcinogenicity. Based on analogies with rock wool (read across), it is reasonable to believe that increases in lung cancer or any mesotheliomas are unlikely to be found in the RCF-exposed cohort. RCF producers have developed a product stewardship program to measure and control fiber concentrations and to further understand the health status of their workers.

Man-made mineral fibers and the respiratory tract

Man-made mineral fibers are produced using inorganic materials and are widely used as thermal and acoustic insulation. These basically include continuous fiberglass filaments, glass wool (fiberglass insulation), stone wool, slag wool and refractory ceramic fibers. Likewise, in the last two decades nanoscale fibers have also been developed, among these being carbon nanotubes with their high electrical conductivity, mechanical resistance and thermal stability. Both man-made mineral fibers and carbon nanotubes have properties that make them inhalable and potentially harmful, which have led to studies to assess their pathogenicity. The aim of this review is to analyze the knowledge that currently exists about the ability of these fibers to produce respiratory diseases.

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

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.

Exposures to refractory ceramic fibers in manufacturing and related operations: a 10-year update

Refractory ceramic fiber (RCF) is a man-made vitreous fiber used for its insulating properties. Since 1987, the work environment of approximately 800 persons employed in fiber manufacture or production operations directly related to manufacturing has been monitored to evaluate exposure levels. Samples were collected quarterly from the breathing zones of randomly selected workers. The measurements from those working in areas of similar activities and exposure controls (dust zones or homogeneous exposure groups) were used to calculate a mean exposure during identified time periods. Persons who spent all of their work time in one zone/group were assigned this mean exposure; those with responsibilities in more than one area were assigned an exposure based on a time-weighted formula. A total of 3213 measurements were used to estimate exposure for 130 job titles; because of the mobile jobs, many samples contribute to the estimates of exposure for multiple job titles. The majority of exposure estimates (53%) have remained stable over the operational history of the plant reported here. For 32 job titles (25%) exposures have decreased, and for 28 job titles (22%) exposures have increased. Of the 122 job titles active in 2001, 97 (79%) exposures were estimated to be at 0.25 f/cc or lower; 8 (7%) had an exposure exceeding 0.5 f/cc (range 0.51-0.80) and 17 (14%) of these exposure estimates were in the range of > 0.25 f/cc to 0.5 f/cc. The continuing program to measure exposure supports a respiratory health surveillance program in these facilities.

Quantitative risk analyses for RCF: survey and synthesis

Refractory ceramic fiber (RCF) is a high-temperature insulating fiber used principally in industrial applications. Epidemiological studies on occupationally exposed cohorts have not indicated that exposure leads to fibrosis, increased lung cancer, or mesothelioma. However, inhalation bioassays with rats and hamsters have shown that these animals can develop each of these endpoints when exposed to high levels of RCF-particle mixtures. This work summarizes relevant quantitative risk analyses based upon analysis of the rat bioassay studies, which lead to predicted unit risks that range nearly three orders of magnitude. Additionally, we identify key assumptions that affect the risk estimates and provide additional estimates using the benchmark dose methodology favored by the U.S. EPA in cases where mechanistic models are inadequate or not available. We show that a key determinant of risk is how lung burdens are normalized (e.g., in terms of the number of fibers per square centimeter of lung surface or the number of fibers per milligram dry lung) for species conversion. Plausible values of unit potency/risk range from 1.4x10(-4) to 7.2x10(-4), neglecting any allowance for the effects of particulate material in the RCF tested in the bioassay experiments.

Mortality of workers occupationally exposed to refractory ceramic fibers

This study was prompted by refractory ceramic fibers (RCF) inhalation studies at high dose levels in animals that demonstrated positive effects for lung fibrosis, mesothelioma, and lung cancer. Current and former male workers employed between 1952 and 2000 at two RCF manufacturing facilities were followed to investigate a possible excess in mortality. The mortality analytic methods included: (1) standardized mortality ratios comparing this cohort to the general and state populations, and (2) a proportional hazards model that relates risk of death to the lifetime cumulative fiber-months/cc exposure among the RCF cohort, adjusted for age at hire and for race. There was no excess mortality related to all deaths, all cancers, or malignancies or diseases of the respiratory system including mesothelioma, but there was a statistically significant association with cancers of the urinary organs SMR = 344.8 (95% CL of 111.6, 805.4). The quality of the data for job history, exposure, and smoking history were very high. Although the cohort was relatively small and young with an average age of 51, the mean latency period was over 21 years. Because of these limitations, the preliminary findings warrant the continuation of this mortality registry for future analyses.