Measurements of airborne asbestos fibres during refurbishing.

Although the use of asbestos fibres in building materials has been prohibited in Norway since 1985, asbestos-containing materials (ACMs) are still found in many buildings. Lack of knowledge and awareness of these materials may lead to exposure during refurbishing. The aim of this study was to investigate the airborne fibre concentration and classify fibres found during the abatement of various ACMs. The release of fibres during short-term work tasks, such as drilling and sawing, was also investigated. Parallel air samples were collected during asbestos abetment of different building materials and analysed with scanning electron microscope (SEM) and phase-contrast microscope (PCM), respectively. Material samples were analysed with SEM. A real-time fibre monitor was used to measure asbestos during short-term work. The highest fibre concentrations were measured for samples collected during the removal of asbestos insulating boards (1.5-4.5 fibres/cm3 [f/cm3]), and the numbers were relatively similar for SEM and PCM. A large difference in asbestos concentrations was found between SEM and PCM when analysing floor materials, which were probably caused by a high number of gypsum fibres that the PCM operator counted. Thin fibres (<0.2 µm in width) were included in the SEM count and constituted up to 50% of the total fibre concentration for the asbestos cement materials. The presence of other inorganic and organic fibres on these samples probably led to similar results between SEM and PCM. Short-term work led to peak concentrations above 30 f/cm3.

Size distribution and single particle characterization of airborne particulate matter collected in a silicon carbide plant.

The global SiC market is projected to grow in the coming years, and research on potential health effects as well as epidemiological studies is therefore of importance. A detailed characterization in terms of the phase composition, morphology and mixing state of airborne PM is still missing, though highly necessary to identify sources and to understand the risk factors in this industry. Particles in the size range of 10 nm to 10 µm were collected with a 13-stage NanoMOUDI impactor in the Acheson Furnace Hall as well as in processing departments during two sampling campaigns. Particle mass concentrations, including the fraction of ultrafine particles (UFPs), were lower in the processing departments in comparison to those in the Acheson Furnace Hall. The particle number size distribution measured with a scanning mobility particle sizer confirmed the low amount of UFPs in the processing departments compared to the furnace hall. Significant differences in the particle mass concentration and distribution were observed in the Acheson Furnace Hall during the two sampling campaigns. The PM size distribution depends upon the sampling location, on the cycle of the nearby furnaces and on special incidents occurring during a furnace run. Scanning and transmission electron microscopy (SEM and TEM) showed that the size range of 0.32-10 µm (aerodynamic diameter) is dominated by carbon (C)-rich particles, which were identified as petroleum coke, graphite, soot and amorphous spherical C-rich particles. Soot was further classified into three types based on the primary particle size, morphology and composition. Diesel-powered vehicles, pyrolysis of petroleum coke and incomplete combustion of volatile components from this pyrolysis are suggested as sources of different soot particle types. Amorphous spherical C-rich particles were also sub-classified based on their morphology and composition as tar balls (TBs) and C-spherical type 2. The amount of SiC fibers and crystalline SiO2 was found to be low. In the size fraction below 0.32 µm (aerodynamic diameter), sulphur (S)-rich particles dominate. This knowledge of the particle size distribution, and chemical and physical properties of the PM occurring in the SiC production is fundamental for an appropriate risk assessment, and these findings should have implications for future epidemiological studies and for the mitigation of worker exposure.

Cellular responses of human astrocytoma cells to dust from the Acheson process: An in vitro study.

Silicon carbide (SiC) is largely used in various products such as diesel particulate filters and solar panels. It is produced through the Acheson process where aerosolized fractions of SiC and other by-products are generated in the work environment and may potentially affect the workers' health. In this study, dust was collected directly on a filter in a furnace hall over a time period of 24h. The collected dust was characterized by scanning electron microscopy and found to contain a high content of graphite particles, and carbon and silicon containing particles. Only 6% was classified as SiC, whereof only 10% had a fibrous structure. To study effects of exposure beyond the respiratory system, neurotoxic effects on human astrocytic cells, were investigated. Both low, occupationally relevant, and high doses from 9E-6µg/cm2 up to 4.5µg/cm2 were used, respectively. Cytotoxicity assay indicated no effects of low doses but an effect of the higher doses after 24h. Furthermore, investigation of intracellular reactive oxygen species (ROS) indicated no effects with low doses, whereas a higher dose of 0.9µg/cm2 induced a significant increase in ROS and DNA damage. In summary, low doses of dust from the Acheson process may exert no or little toxic effects, at least experimentally in the laboratory on human astrocytes. However, higher doses have implications and are likely a result of the complex composition of the dust.