Size Distribution and Lung-Deposition of Ambient Particulate Matter Oxidative Potential: A Contrast between Dithiothreitol and Ascorbic Acid Assays

Abstract

This study aims to investigate the lung deposition doses (LDDs) of different particle sizes and assess their oxidative potential (OP) using dithiothreitol (DTT) and ascorbic acid (AA) assays. Particles of aerodynamic sizes of <0.49, 0.49-0.95, 0.95-1.5, 1.5-3, and 3-7.2, >7.2 µm were collected in a residential/commercial site of a port city in East China. The OP activity of water-soluble and methanol-soluble fractions were highest in quasi-ultrafine (quasi-UFP, <0.49 µm), followed by coarse particles (CP, 3-7.2 µm). Secondary organic aerosols (SOAs) might have contributed to the high OP of quasi-UFP, as evident in the OP correlating strongly with O3 (r=0.60), moderately with ambient temperature (r=0.58), and negatively with NO2 (r=-0.53). LDDs of particles and OP in different respiratory regions were estimated using the Multiple-Path Particle Dosimetry (MPPD) model. AA measured higher OP deposition of coarse particles than DTT in the head, and the two assays predicted similar patterns of OP deposition of quasi-UFP in the tracheobronchial and pulmonary regions. LDD correlated strongly with intrinsic OP (pmol min-1µg-1) and weakly with extrinsic OP (nmol min-1m-3), indicating the reactive oxygen species (ROS) generation capacity of ambient particles and the contribution of the chemical compositions to the health risk. Water-soluble trace metals correlate more with extrinsic OP than intrinsic OP supporting the use of extrinsic OP for assessing ambient particles health risk. The decline of the OP with the increase in LDD is due to antagonistic interactions between chemical compositions. OP of quasi-UFP dominated in alveoli, while those of fine and coarse particles dominated in the head. The results contribute to the knowledge gap of OP distribution and health risks of ambient particles in specific regions of human lungs.

Keywords: Size distribution, Particulate matter, Oxidative potential, MPPD, Lung-deposition, Dithiothreitol, Ascorbic acid