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Bulk Density Measurements Using an Air Comparison Pycnometer
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... Aerodynamic diameter d a is a key parameter for characterizing particle deposition by inertial impaction. The oblate spheroid has been widely used in the aerodynamics calculation for plate-like particles in previous research [35][36][37][38]. Cheng et al. [36] studied the aerodynamic properties of plate-like talc particle and established the relationship between aerodynamic diameter and projected area diameter. ...
With the wide applications of graphene nanoplatelets (GNPs) in the industries, more concerns are raised about the effectiveness of filtration technology to control GNPs release during manufacturing and handling processes. Accurate prediction of the capture efficiency of airborne GNPs is significant to avoid occupational exposure. Herein, the aerodynamic property and filtration mechanisms of airborne GNPs with plate-like shape and folded structure were studied. Different equivalent diameters of GNPs (aerodynamic diameter da, mobility diameter dm) were derived and used to describe diverse mechanisms in the filtration model. The capture efficiency of plate-like GNPs and sphere-like NaCl particles was measured with Nuclepore membranes and nanofibrous membranes to assess the particle shape effect during filtration. The plate-like GNPs showed higher capture efficiency due to the larger interception length. SEM measurement showed that not only planar GNPs, GNPs with folded structure also occurred due to the large lateral size to thickness ratio and strong mechanical stimulation in the atomization process. For GNPs with aerodynamic diameter of 0.5 – 0.9 μm, the capture efficiency for folded GNPs decreased by 20 – 30% according to the analytical calculation. In addition, the effects of membrane structural parameters (Nuclepore membrane pore radius, fiber diameter, solidity) on the quality factor (Qf) were systematically analyzed to evaluate the overall filtration performance. This study not only elucidates the effect of plate-like shape and folded structure on the aerodynamics of airborne GNPs, but also contributes to better design of Nuclepore and nanofibrous membranes to improve the filtration performance of plate-like particles.
This paper will only consider the risk of non malignant pulmonary disease (“Silicatosis”) associated with the inhalation of phyllosilicate dust at the workplace. Other sources of exposure were dealt with by Drs BOUTIN and VIALLAT at this conference and evaluation for carcinogenicity is the role of the International Agency for Research on Cancer (IARC). Among the non fibrous phyllosilicates, only talc has been evaluated for carcinogenicity (World Health Organization 1978). According to IARC, there is inadequate evidence for the carcinogenicity to humans of talc not containing asbestiform fibres, while there is sufficient evidence for the carcinogenicity to humans of talc containing asbestiform fibres.
The relationship between the inhalation exposure concentration of talc and the resulting lung burdens and histologic lesions was studied using groups of 20 F344/Crl rats and 20 B6C3F mice (10 male and 10 female) exposed to one of three concentrations of asbestos-free talc for 6 hr/day, 5 days/week for 4 weeks. Controls were exposed to filtered air using the same schedule. The pulmonary retention of talc and the development of pulmonary pathology were evaluated. The mass median aerodynamic diameter (MMAD) of the talc aerosol was 3.0 microns with a geometric standard deviation (sigma g) of 1.9. The mean exposure concentrations for rats were 0, 2.3, 4.3, and 17 mg talc/m3. Lung burdens in rats averaged 0, 0.07, 0.17, and 0.72 mg talc/g lung after the 20-day inhalation exposure; thus, the amount retained in the lung per unit of exposure concentration increased with increasing concentration. Mean exposure concentrations for the mice were 0, 2.2, 5.7, and 20.4 mg of talc/m3, which resulted in lung burdens of 0, 0.10, 0.29, and 1.0 mg talc/g lung; thus, the relationship between exposure concentration and the amount retained in the lung was approximately constant. Lung burdens from this study were used to project lung burdens that would result from longer exposures of rodents and man. No clinical signs were observed in the rats or mice prior to sacrifice 24 hr after the last exposure day. Histologic alterations in lung tissue consisted of only a modest, diffuse increase of talc-containing, free macrophages within alveolar spaces in both rat and mouse groups exposed to the highest level of talc for 20 days. A model simulating chronic talc inhalation exposure of rats and mice predicted lung burdens of 2-3 mg talc/g lung (wet wt) if animals were exposed to 17 mg talc/m3 for 2 years, and deposition and clearance of talc were unchanged by continued exposure. A potential limitation in this modeling is that if clearance of talc is delayed by continued exposure, the accumulated talc lung burdens would be higher than those projected by the simulation model. Humans exposed to aerosols of respirable talc are projected to accumulate much higher lung burdens than would occur in rodents exposed to the same aerosol, because humans have a higher estimated deposition fraction and slower estimated clearance of the deposited talc dust. Equilibrium lung burdens of greater than or equal to 2 mg talc/g lung were predicted for human exposures at or near the TLV for talc.
Metal tritide is widely used for research, purification, compression, and storage of tritium. The current understanding of metal tritide and its radiation dosimetry for internal exposure is limited, and ICRP publications do not provide the tritium dosimetry for hafnium tritide. The current radiation protection guidelines for metal tritide particles (including hafnium tritide) are based on the assumption that their biological behavior is similar to tritiated water, which is completely absorbed by the body. However, the solubility of metal tritide particles depends on the chemical form of the material. The biological half-live of hafnium tritide particles and the dosimetry of an inhalation exposure to those particles could be quite different from tritiated water. This paper describes experiments on the dissolution rate of hafnium tritide particles in a simulated lung fluid. The results showed that less than 1% of the tritium was dissolved in the simulated lung fluid for hafnium tritide particles after 215 d. The short-term and long-term dissolution half times were 46 and 4.28 x 10(5) d, respectively. This indicates that hafnium tritide is an extremely insoluble material. Self-absorption of beta rays in the hafnium tritide particles was estimated by a numerical method. The dose coefficients were calculated as a function of particle size using in vitro solubility data and a calculated self-absorption factor. The dose coefficient decreased with aerodynamic diameters in the range of 0.25 to 10 microm, mainly because the self-absorption factor decreased with increasing particle size. For a particle 1 microm in aerodynamic diameter, the dose coefficient of a hafnium tritide particle was about 10 times higher than that of tritiated water but was about 1.4 times lower than that calculated by ICRP Publication 71 for Type S tritiated particles. The ICRP estimate did not include a self-absorption factor and thus might have overestimated the dose. This finding has significant implications for current health protection guidelines.
