Potential genotoxic effects of diffusion flame-derived particulate matters (PMs), known to cause various adverse health problems, doped with iron, one of the representative heavy metals frequently found in the atmosphere, were examined. B6C3F1 mice were exposed to PMs [chamber 1 (low), 100; chamber 2 (middle), 200; and chamber 3 (high), 400 microg/m3] for 6 h/day, 5 days/week for one, two and four weeks in 1.5 m3 whole-body inhalation chambers. Our diffusion flame system produced 94.8 and 5.2% fine PM2.5 and PM10, respectively, with 89% of PM2.5 sized between 0.1 and 0.2 microm. Two cytogenetic endpoints were investigated through chromosomal aberration and supravital micronucleus (SMN) assays. Frequencies of cells with chromosome aberration (%) were observed in time- and concentration-dependent manners except in one-week exposure group, as also observed in SMN study. Generally, noniron flame induced less chromosome aberration than iron-doped flame, an indication that iron particles could potentiate urban PM toxicity. The above results indicate our diffusion flame system generated genotoxic fine PMs, whose effects were potentiated by organometallic particles such as iron. Our system can provide reliable PM models for studying the toxicity of urban fine PMs applicable for risk assessment.

The present work investigated the effects of Al, Si, and N content on the impact toughness of the coarse-grained heat-affected zone (CGHAZ) of Ti-containing low-carbon steel. Simulated CGHAZ of differing Al, Si, and N contents were prepared, and Charpy impact toughness was determined. The results were interpreted in terms of microstructure, especially martensite-austenite (M-A) constituent. All elements accelerated ferrite transformation in CGHAZ but at the same time increased the amount of M-A constituent, thereby deteriorating CGHAZ toughness. It is believed that Al, Si, and free N that is uncombined with Ti retard the decomposition of austenite into pearlite and increase the carbon content in the last transforming austenite, thus increasing the amount of M-A constituent. Regardless of the amount of ferrite in CGHAZ, its toughness decreased linearly with an increase of M-A constituent in this experiment, indicating that HAZ toughness is predominantly affected by the presence of M-A constituent. When a comparison of the effectiveness is made between Al and Si, it showed that a decrease in Si content is more effective in reducing M-A constituents.