Mitsutoshi Takaya

Genotoxicity and cytotoxicity of multi-wall carbon nanotubes in cultured Chinese hamster lung cells in comparison with chrysotile A fibers.

Genotoxicity and Cytotoxicity of Multi‐wall Carbon Nanotubes in Cultured Chinese Hamster Lung Cells in Comparison with Chrysotile A Fibers: Masumi Asakura, et al. Japan Bioassay Research Center, Japan Industrial Safety and Health Association

Approach to the Exposure Assessment of MWCNT by Considering Size Distribution and Oxidation Temperature of Elemental Carbon

Multi-walled carbon nanotubes (MWCNTs) have many beneficial characteristics, but it is concerned that exposure to MWCNTs may pose health risks. As an approach to the quantitative exposure assessment of MWCNTs, we have characterized and determined MWCNTs by elemental carbon (EC) using an aerosol carbon monitor. The EC fractions oxidized at different temperatures correspond sample characteristic such as diameter of MWCNT or origins of particles. As MWCNTs aggregate/agglomerate easily, they are usually observed as micron-size particles. Whereas, EC contained in ambient particulate matter (APM) is mainly observed in fine particles. Therefore, the size of airborne particles is a good parameter to distinguish MWCNT from other carbonaceous particles, especially APM. The size and oxidized temperature of EC suggested the origin of the carbonaceous aerosol samples. Exposure assessment of MWCNT was conducted by utilizing the size distribution of EC in the environment where particulate MWCNT or MWCNT-containing composite was handled. A procedure for exposure assessment of MWCNT-related workplace is proposed.

Performance evaluation of newly developed portable aerosol sizers used for nanomaterial aerosol measurements.

Nanomaterial particles exhibit a wide range of sizes through the formation of agglomerates/aggregates. To assess nanomaterial exposure in the workplace, accurate measurements of particle concentration and size distribution are needed. In this study, we evaluated the performance of two recently commercialized instruments: a portable scanning mobility particle sizer (SMPS) (NanoScan, TSI Inc.), which measures particle size distribution between 10 and 420 nm and an optical particle sizer (OPS, TSI Inc.), which measures particle size distribution between 300 and 10,000 nm. We compared the data measured by these instruments to conventional instruments (i.e., a widely used laboratory SMPS and an optical particle counter (OPC)) using nano-TiO2 powder as test aerosol particles. The results showed obvious differences in the size distributions between the new and old SMPSs. A possible reason for the differences is that the cyclone inlet of the new SMPS (NanoScan) acted as a disperser of the weakly agglomerated particles and consequently the concentration increased through the breakup of the agglomerates. On the other hand, the particle concentration and size distributions measured by the OPS were similar to the OPC. When indoor aerosol particles were measured, the size distribution measured by the NanoScan was similar to the laboratory SMPS.

Examination of validity of a conditioned odor aversion (COA) procedure using low-dose of organic solvent as an applied procedure of the conditioned taste aversion

Smell of very low dose of chemical might evoke subjective physical symptoms in human by some process of learning named the aversion conditioning. But few scientific evidences of the hypothesis have been reported so far. Validity of conditioned odor aversion (COA) using low-doses of organic solvent as odor conditioned stimulus (CS) was examined. In conditioning phase, water-deprived male Sprague-Dawley rats were presented low, medium or high dose solution for 30 min followed by 0.3 M Lithium Chloride (LiCl) solution or saline injection. The xylene solution and drink water were simultaneously provided on the next day as two-bottle test. Consumption of medium dose of xylene solution was significantly decreased in LiCl injection group as compared with saline group. There was no difference between LiCl and saline injected animals in low group. Animals in high dose did not access to xylene even on the conditioning. These results indicate that animals showed high sensitivity for discrimination against concentration of xylene and that the medium dose of xylene functioned as the CS. We concluded that the COA used in the present study may be one of useful procedures to investigate olfaction of animal.