Table 2 - uploaded by Larry Glass
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To review the scientific literature on the health effects of refractory ceramic fibres (RCFs). The adverse effects of exposure to asbestos has led to concern about the potential for other fibrous materials to cause diseases. For this reason the human populations most heavily exposed to synthetic mineral fibres have been examined for any adverse eff...
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Citations
... The ®bres used were allocated to categories of pathogenic or non-pathogenic, depending on whether they caused tumours and ®brosis in recent inhalation studies (Davis et al., 1996;Glass et al., 1995;Hesterberg et al., 1993). Pathogenic ®bres were Long Fibre Amosite, Silicon carbide and RCF1; non-pathogenic ®bres were RCF4, Code 100/475 and MMVF10. ...
... were carried out at a target concentration of 1000 ®bres/ml and the number of deposited long ®bres was similar for amosite asbestos and Code 100/475, but there were no tumours in the case of the latter. In the RCC (Research Consultancy Co., Geneva, Switzerland) studies, where MMVF10 and RCF4 were found to be non-pathogenic, the dosimetry again showed similar numbers of deposited long ®bres for all of the dierent ®bres tested, yet still some ®bres were tumorigenic (for example RCF1), and some were not (RCF4 and MMVF10) (Bunn et al., 1992;Glass et al., 1995;Hesterberg et al., 1993). These data strongly support a dierence in carcinogenic potency between the ®bres and not a dierence that can be explained as dierences in eective dose to the lung for the dierent ®bres. ...
The aim of the study was to develop a simple short-term in vitro assay which would allow us to predict the pathogenicity of fibres based on data already available from in vivo studies. Fibres were used naked (uncoated) or coated with rat IgG, or rat or sheep surfactant. The fibres were used to stimulate superoxide anion release by rat alveolar macrophages. Binding of fibres to rat alveolar macrophages was assessed by optical microscopy. Fibres used in the naked state produced little or no stimulation of superoxide anion from rat alveolar macrophages. When fibres were coated with rat IgG there was a significant increase in superoxide release for all fibre types with the exception of RCF4 and Code 100/475. When fibres were coated with rat or sheep surfactant, there was suppression of the respiratory burst for all fibre types. The observed suppression was not due to a scavenging effect by the surfactant itself, because xanthine/xanthine oxidase generated superoxide was unaffected by surfactant. The suppressive effect was shown to act directly on the macrophages. Comparing naked and coated fibres for their ability to bind to macrophages, it was shown that in general more coated fibres were bound and that increased binding was associated with suppressed superoxide release for both types of surfactant-coated fibres. It was concluded that the nature of the fibre coating is the main factor influencing the interaction between fibres and macrophages. The type of binding through different receptors may either stimulate or switch off the respiratory burst. The assay used here does not, however, allow any predictions to be made regarding the pathogenicity of fibres.
... In addition the chemical composition of RCF makes it more durable in biological systems than most other commercial SMF. These factors of diameter, dose and biological durability have been recognised from experiences in asbestos and other natural and synthetic mineral fibres as major influences on fibre toxicity and carcinogenicity (Glass et al., 1995). In 1988 as a result of increasing concern within the community about the possible health effects from exposure to SMF the National Occupational Health and Safety Commission established a Technical Working Group to investigate typical levels of exposure in manufacturing and user industries and possible health effects and, based on available information, recommend exposure standards and safe working practices. ...
... Through the tripartite and public comment processes the Commission declared a national exposure standard of 0.5 fml" 1 for all types of SMF and a secondary standard of 2 mgm~ 3 of inspirable dust to protect against upper respiratory tract irritation from large diameter non-respirable fibre (Worksafe, 1990). Since 1990 representatives from the original Technical Working Group have updated the Commission on an annual basis with a review of the considerable published and unpublished research developments on in vitro testing, animal experiments and epidemiological and exposure investigations in the SMF industry most of which has now been recently formally reviewed (Glass et al., 1995). This study provides an overview of a more detailed and up to date analysis which is currently being undertaken into the health status of the Australian RCF manufacturing workforce. ...
Refractory ceramic fibre (RFC) is a subset of synthetic or vitreous mineral fibres (SMF) being composed of aluminium and silicon oxides. They have a high melting point and hence provide insulation application at temperatures up to 1400°C. To achieve the insulation properties, fibre is manufactured with nominal diameters of around 3-4 micrometers which is finer than other major commercial SMF types. In most instances the produce is manufactured without binder which with its finer fibre diameters results during handling in the generation of larger quantities of respirable fibres than does other commercial SMF. In addition the chemical composition of RCF makes it more durable in biological systems than most other commercial SMF. These factors of diameter, dose and biological durability have been recognised from experiences in asbestos and other natural and synthetic mineral fibres as major influences on fibre toxicity and carcinogenicity (Glass et al., 1995). In 1988 as a result of increasing concern within the community about the possible health effects from exposure to SMF the National Occupational Health and Safety Commission established a Technical Working Group to investigate typical levels of exposure in manufacturing and user industries and possible health effects and, based on available information, recommend exposure standards and safe working practices. In examining data derived from the Australian RCF industry, the Technical Group found upper respiratory tract irritation at concentrations above 1 fml" 1 and for employees under medical surveillance (cross-sectional studies) no evidence of lung fibrosis. In terms of evidence for cancer, no suitable epidemiological studies were found anywhere for determining lung cancer or mesothelioma risk although data from the Australian Mesothelioma Surveillance Program indicated no cases associated with the manufacture of SMF (Worksafe, 1989). As part of its recommendations the Technical Group prepared a standardised membrane filter method for monitoring airborne SMF fibres and a gravimetric method for inspirable dust. Through the tripartite and public comment processes the Commission declared a national exposure standard of 0.5 fml" 1 for all types of SMF and a secondary standard of 2 mgm~ 3 of inspirable dust to protect against
... However problems in interpretation remain (e.g. Brown et al., 1995). While positive results can be obtained in animal experiments studies of human populations exposed to RCFs have revealed no ill health (reviewed Glass et al., 1995). However the RCF industry remains determined to ensure the safest possible practices in the manufacture and use of its products and to do so in as public a way as possible; thus providing increasing reassurance to its workers, customers and regulators. ...
This report shows the actual state of workplace exposure to refractory ceramic fibres (RCF) in Germany in comparison with international results. It is also demonstrated how the exposure has changed from 1992 to 1996. The report also examines with two examples what kind of further development of RCF exposure can be expected. Further on a comparison is made between the dustiness of RCF products versus polycrystalline alumina fibres and the new less biopersistent high temperature glass fibres (HTGF) using laboratory shaking tests and actual measurements in practice. It is shown that the actual state of technology is around 0.5 fibres/ml for processing of RCF products and that the variations of measured exposure in case of repetitive measurements is important in comparison to the actual valid workplace limit value and therefore individual measurements can not be considered as a proof for an exposure improvement. It is also shown that further improvements of the state of technology is only possible in long term with high efforts in changing work processes. The report demonstrates clearly, that the dustiness of HTGF is similar to RCF and thereFore the health and safety improvements due to their lower biopersistence are not compromised by an increase of exposure.
The three variables, dose, dimensions and durability, have been shown from many studies to be the factors that combine to give the potential for a fibre to cause respiratory diseases. Considering durability, a fibre that could show increased dissolution, possibly accompanied by chemical change, in physiological solutions would be expected to show a reduced persistence in the lungs and have a lower potential for producing respiratory diseases. The development of such a fibre, Superwool X607, and the understanding that has been acquired in terms of solubility rate and other fibre properties is presented in this paper. The importance of in-vitro solubility rate studies to screen potentially useful fibre compositions, combined with an understanding of how these compositions can be selected using free energy of hydration or non-bridging oxygen theories, is discussed in terms of developing new less "in-vivo" durable fibres.
Introduction
The pleura is host to many diseases, some systemic, others spreading from the underlying lung. Lung carcinoma metastases are the commonest lesions seen by pathologists. The most frequent cause of pleural problems is an effusion, secondary to congestive cardiac failure. This chapter will consider normal pleural physiology, as well as benign and malignant processes.
The pleural space, separating the lung and chest wall, contains a small amount of liquid that lubricates the pleural surfaces during breathing (see Chapter 1). The volume of fluid in the pleural space is small, in the range of 0.2–0.5 ml. Normally, the protein and cellular content is low, with no inflammatory cells. The thin layer of liquid between the pleural surfaces has the important function of providing mechanical coupling between the chest wall and lung. For this connection to be effective, the volume of pleural liquid required for lubrication must be kept to a minimum. In addition, the colloid osmotic pressure must be low to keep this volume small. This fluid ensures instantaneous transmission of perpendicular forces between the two structures, and allows their sliding movement in response to shearing forces.
Banishment of asbestos in many industrialized countries needs to significantly evaluate the potential adverse health effects of fibres offered as substitutes. This field is wide and heterogeneous. In this paper we tried to review biological and health effects of substitute fibres available on the market. Substitution for asbestos requires several fibrous products, with various chemical composition and different properties. Among these properties, protection against high temperatures, is a real problem. Fibres are divided into natural and synthetic fibres, either inorganic or organic. Presently, there is no final definite answer to the question of the potential adverse effects of substitute fibres on the health of exposed workers. The epidemiological studies carried out on cohorts of workers employed in the production of man-made mineral vitreous fibers have shown an excess of mortality by lung cancer; however, it is not obvious that these fibres were the cause of this excess. Considering data from animal inhalation studies and first results from morbidity studies in workers exposed to refractory ceramic fibres (RCF), it is essential to be vigilant towards the use of RCF. In general, fibre manufacturers are trying to develop new fibres with low biodurability. New synthetic vitreous fibres resistant to high temperatures (above 1000°C), with a chemical composition different from that of RCF, showing a short biopersistence in vivo, appear to be promising. Nevertheless it is essential to wait for results of chronic animal inhalation bioassays. Concerning other fibres (natural inorganic fibres, synthetic organic and inorganic fibres), there are few or no data available. In some cases, toxicity of new fibres seems to have been inadequately assessed before their marketing. Considering the permanent development and the complexity of fibrous materials, a toxicological surveillance of chronic inhalation bioassays and epidemiological studies are needed.
With the growing regulatory attention on fibrous materials has come the suggestion that manmade vitreous fibres (MMVFs) should be classified from a hazard point of view using a matrix based on their fibre diameter and composition. There is, therefore, a need for a reproducible procedure to assess the mean diameter of fibrous products. Due to the shape of the fibre diameter distributions, this has focused on methods to give the length weighted geometric mean. The present paper describes the development and refining of a scanning electron microscopy (SEM) based method for determining the length weighted geometric mean diameter for a fibre sample. An optimised protocol, including a semi-automated method, was established and assessed by two laboratories, including a repeat assessment at one laboratory, giving a range of 0.09 μm on the same fibrous material, with a mean diameter of 1.57 μm.
Pleural plaques among pumice workers on Lipari Island have been described and the Authors have suggested the hypothesis that such biological effect could be related to the particles' morphology characterized by the presence of elements similar to fibers. Analysis on compact bulk materials and on dust samples from different sites of the Island have been performed to obtain information on the chemical composition of such materials. The Scan Electron Microscopy (SEM) analyses confirm the presence of fibrous particles with a chemical structure similar to the Refractory Ceramic Fibers (RCF) composition. These results could explain the presence of plural plaques among the workers and new clinical and epidemiological evaluations of the potential effects associated to this exposure are needed.
Diffuse pleural thickening and circumscribed pleural plaques are two nonmalignant pleural diseases caused by asbestos exposure. It has generally been accepted that diffuse pleural thickening is associated with measurable pulmonary impairment and clinical symptoms; however, the functional impact of asbestos-induced pleural plaques still remains controversial. Recent literature suggests that asbestos-induced pleural plaques are associated with ventilatory impairment and respiratory symptoms. We critically analyzed the literature from 1965 to 1999 evaluating this potential relationship. We conclude that: (1) individuals with asbestos-induced pleural plaques may have alterations in pulmonary function and/or clinical symptoms that are independent of smoking and radiographic parenchymal fibrosis; and (2) the respiratory changes due to asbestos-induced pleural plaques are generally less severe than those caused by diffuse pleural thickening. The mechanism of the pulmonary functional changes associated with pleural plaques has not been elucidated.
