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Ultrafine particles (UFPs, < 2.5 µm) in air pollutants have been identified as a major cause of respiratory diseases, since they can affect the lung alveoli through the bronchus. In particular, if toxicants such as heavy metals and polycyclic aromatic hydrocarbons (PAHs) are present in UFPs, they can cause diseases such as asthma, chronic obstructive pulmonary disease, and lung cancer. This study compared in vitro toxicity of various particulate matter including UFPs from combustion particles of diesel (diesel exhaust particles (DEP)), rice straw (RS), pine stem (PS) and coal (CC), and road dust particles from tunnel (TD) and roadside (RD). UFPs from combustion particles and road dust were collected with a glass fiber filter using burning systems and a solid aerosol generator. Cell viability was determined by neutral red uptake assay using Chinese hamster ovary strain K1 cells. Redox cycling activity and intracellular reactive oxygen species were measured using 1,4-dithiothreitol (DTT) and 2',7'-dichlorofluorescin diacetate (DCF-DA) assay, respectively. Our in vitro studies validated that combustion particles had high toxicological activity. PS demonstrated the highest activity in cytotoxicity but DEP had the highest activity in the DTT and DCF-DA assays. Overall, since the toxicological activity of particles generated by various means was different, risk assessment should be conducted through various toxicity evaluations rather than one toxicity evaluation.

Debt-to-income ratio is defined as the ratio between total household debt and disposable income for households and private unincorporated enterprises. Debt-to-asset ratio is defined 164 Chang-Gyun Park Fig. 5.2 Trend in ability-to-repay indicators Source: Bank of Korea. Notes: Debt-to-income ratio is the ratio between household debt and household disposable income. Debt-to-asset ratio is the ratio between individual debt and asset in the Flow of Funds table. Source: Bank of Korea. Notes: Housing finance institutions include the Korea Housing Finance Corporation and the National Housing Fund. Other deposit-taking institutions include savings banks, credit unions, and mutual saving cooperatives.