10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Improvement of Inhalation Toxicity Testing for Nanomaterials and Compliance Monitoring for Ambient PM
Jun Kanno, Chuen-Jinn Tsai, Japan Bioassay Res. C. Kanagawa; Natl. Chiao-Tung U., Taiwan
Abstract Number: 1731 Working Group: Invited by Conference Chair
Abstract For the new nanomaterials (NM), in general, there is no pre-existing knowledge to suggest its toxicity. Therefore, whole-body inhalation toxicity study is the first choice considering the most important route of exposure to humans. Yet, “inhalation” is a big hurdle for toxicologists; facilities are expensive to build and run, and requires skillful operators. Methods to generate well-dispersed aerosol and quantitate the aerosol density require case-by-case innovation, which is costly and time consuming. In order to overcome such hurdles, we developed the “Taquann” dispersion method and a “direct injection” whole body inhalation system. The dispersion method is based on two concepts: liquid-phase fine filtration and critical point drying to avoid re-aggregation by surface tension. Briefly, the bulk sample is suspended and dispersed in tert-butyl alcohol, filtered by a fine mesh to remove aggregates/agglomerates, snap-frozen by liquid nitrogen, and vacuumed, mimicking the process of critical point drying. Then aliquots of dry dispersed sample are periodically injected to the chamber system by the compressed air to maintain the aerosol concentration in the exposure chambers. This method is shown to be applicable to Mitsui-7 and Nikkiso MWCNTs, three different makes of nano-TiO2, potassium titanate whiskers, and others. The advantages of this system is its cheapness and easy operation, high adjustability to various NM samples, low chance of polluting the facility, and low loss of sample. We believe our new system makes inhalation studies much popular to facilitate the risk assessment of not only various new NMs but also any other particulate matters including PM2.5 from various origins.
While NM risk assessment is conducted in vivo or in vitro, most epidemiological studies link human health impacts to PM2.5 mass measured at ambient environment. FRM PM2.5 samplers and FEM monitors are used as compliance monitors, which make use of size-selective inlets followed by a filter to collect particles for further analysis. However, PM2.5 concentrations determined by the FRM samplers are not true concentrations due to the uncertainties in the evaporation loss of volatile aerosol materials and water associated with aerosols during aerosol sampling and conditioning. The differences between PM2.5 FEM and FRM concentrations often exist and increase with decreasing PM2.5 concentrations. This talk will address the improvement in PM10 and PM2.5 inlets, and aerosol conditioning during filter sampling which results in true PM2.5 concentrations. The US EPA PM10 inlet and PM2.5 inlet, including the well impactor ninety-six (WINS) and the very sharp cut cyclone (VSCC) were found to have particle bounce or particle overloading problems, which change the cutoff characteristics and PM concentrations. The grease-coated substrate of the PM10 inlet was replaced by an oil-soaked glass fiber filter to capture particles effectively. The impaction surface of the PM2.5 WINS was re-designed to allow a small amount of water or vacuum oil to inject upward to wash deposited particles off the plate. The modified PM inlets eliminated particle bounce and particle overloading effectively with small errors during long-term sampling. A chilled filter sampler followed by a Nafion dryer was found to suppress the evaporation loss of semi-volatile inorganic materials (SVIM) effectively due to a small amount of water vapor condensation during sampling and conditioning processes. The total evaporation loss of SVIM in PM2.5 measured by chilled filter sampler was effectively reduced and the accuracy of PM2.5 sampling was significantly improved after correcting for the amount of condensed water determined empirically. These improvements lead to accurate PM data that can be related to health effects meaningfully and used to calibrate widely used low-cost PM sensors reliably.