Environ. Sci. Technol. 2009, 43, 6851–6856
Size Distributions of Polycyclic Aromatic Hydrocarbons in the Atmosphere and Estimation of the Contribution of Ultrafine Particles to Their Lung Deposition Y O U H E I K A W A N A K A , * ,† YOSHITERU TSUCHIYA,† SUN-JA YUN,† AND KAZUHIKO SAKAMOTO‡ The Institute of Basic Environmental Research, Environmental Control Center Co., Ltd., 323-1 Shimo-ongata, Hachioji, Tokyo 192-0154, Japan, and Department of Environment Science and Human Technology, Graduate School of Science and Engineering, Saitama University, 255 Shimo-ohkubo, Sakura, Saitama 338-8570, Japan
Received January 6, 2009. Revised manuscript received June 5, 2009. Accepted July 21, 2009.
This is the first estimation of the contribution of ultrafine particles to the lung deposition of particle-bound polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. The size distributions of nine PAHs (4-6 rings) were measured at roadside and suburban sites in winter in Japan. Deposition efficiencies and fluxes of PAHs in ultrafine mode (2.1 µm) to the human respiratory tract were calculated using the LUDEPcomputer-basedmodel.From10%-15%and4.2%-6.9% of target PAHs were distributed in the ultrafine mode in the roadside and suburban atmosphere, respectively. The model calculations showed that as much as 18%-19% and 16%-17% of inhaled PAHs are deposited in the alveolar region of the lung for the roadside and suburban atmosphere, respectively. Total deposition fluxes of target PAHs in the alveolar region were about 1.5-fold greater for the roadside atmosphere than for the suburban atmosphere. Importantly, ultrafine particles were shown to contribute as much as 23%-30% and 10%-16% to PAH deposition in the alveolar region for the roadside and suburban atmosphere, respectively, although the contributions of ultrafine particles to the total particulate matter mass were only 2.3% in the roadside atmosphere and 1.3% in the suburban atmosphere. These results indicated that ultrafine particles are significant contributors to the deposition of PAHs into the alveolar region of the lung.
Introduction Data regarding particle size distributions of atmospheric particulate matter (PM) and particle-bound toxic compounds are essential for the assessment of the influence of PM on human health because the deposition behavior of inhaled PM in the human respiratory tract depends strongly on particle size (1-3). PM is classically grouped into the ultrafine, * Corresponding author phone: +81-42-650-7200; fax: +81-42652-0800; e-mail:
[email protected]. † Environmental Control Center Co., Ltd. ‡ Saitama University. 10.1021/es900033u CCC: $40.75
Published on Web 07/30/2009
2009 American Chemical Society
accumulation, and coarse size modes (4, 5). Ultrafine particles have an aerodynamic diameter (Dp) of less than ca. 0.1 µm; they are emitted from combustion processes and are formed in the atmosphere by homogeneous nucleation. Accumulation mode particles are in the approximate range 0.1 < Dp < 2.0 µm and are formed by coagulation and condensation. Coarse particles, those larger than ca. 2 µm, are formed through mechanical attrition and disintegration processes, such as the wind-blown suspension of land surface dust and soil. Coarse particles are mainly deposited in the extrathoracic region, while some inhaled fine particles reach the alveolar region of the lung. In particular, ultrafine particles are deposited at much higher efficiency in the alveolar region than accumulation mode particles (1-3). In addition, several controlled human exposure studies (6, 7) have demonstrated long-term retention of ultrafine particles deposited in the human lung. Moreover, recent studies have indicated that toxic activities per unit mass of ultrafine particles, such as the mutagenic activity (8) and the redox activity (oxidative stress activity) (9), are significantly higher than those of accumulation mode and coarse particles. Therefore, ultrafine particles may act as efficient carriers of toxic compounds into the pulmonary alveoli and may cause the accumulation of toxic compounds within the lung. Polycyclic aromatic hydrocarbons (PAHs) are mainly formed during incomplete combustion processes of organic matter, such as coal, gasoline, and diesel fuel, and are released into the atmosphere from combustion sources (10). Several PAHs are known to be strong mutagens and potential human carcinogens (10, 11). PAHs have been detected widely in the atmosphere (10). Many studies (12-14) have shown that lifetime lung cancer risk of PAHs in the atmosphere is often higher than 1 in 100,000 (10-5). Therefore, PAHs are especially important compounds in analyses of the particle size distribution in the atmosphere from the viewpoint of their effects on human health. Several studies (8, 15-18) of the particle size distribution in the atmosphere have shown that PAHs are found mainly in fine particles, which can reach the pulmonary alveoli. However, there have been only a few estimates of the respiratory deposition of particle-bound PAHs (13, 19). Very little is known about the contribution rate of ultrafine particles to PAH deposition in the respiratory tract. In fact, not much data is available regarding the concentrations of PAHs in ultrafine mode. Our previous studies (8, 20) indicated that ultrafine particles contain more mutagens, such as PAHs and nitrated-PAHs, than accumulation mode particles. Therefore, we feel that ultrafine particles may be important contributors to PAH deposition in the lung, although the contribution of ultrafine particles to the total PM mass is very small. The present study was performed to determine the detailed size distributions of PAHs from the ultrafine mode to the coarse mode in the roadside and suburban atmospheres, and to estimate the contribution of ultrafine particles to PAH deposition in the lung. The results of this study will be useful to assess the influence of ultrafine particles on human health.
Experimental Section Sampling. PM sampling was performed at a roadside site and a suburban site. The roadside site was located about 1 m from the edge of Prefectural Road 57 in Saitama City, to the north of Tokyo, Japan. The traffic flow at the roadside site was about 19,000 vehicles per day, and the fraction of heavy vehicles was 21% of the total number of vehicles. The VOL. 43, NO. 17, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Size distributions of PM, individual PAHs, and total PAHs in the roadside and suburban atmospheres. PM sampling was performed using a low-pressure cascade impactor in winter. Dotted arrows at 0.12 and 2.1 µm show ultrafine mode and fine mode, respectively, and the corresponding values (%) show the corresponding % contributions to the total mass. suburban site was located within Saitama University in a 0.70-1.2, 1.2-2.1, 2.1-3.5, 3.5-5.2, 5.2-7.8, 7.8-11, and >11 residential area of Saitama City and about 300 m from the µm. As the masses of PM in the
