Oxidative Potential of Size-resolved Ambient Particulate Matter and its relationship with the Respiratory Deposition

Abstract

Particulate matter (PM) has been of great interest since they have been highly correlated to different health problems. Oxidative potential (OP) is one of the proposed metrics in measuring PM’s toxicity. OP is defined as the PM’s capability of inducing the production of reactive oxygen species (ROS). ROS, in turn, causes oxidative stress, and later on affects the over-all condition of the system. Another difficulty in characterizing PM’s toxicity is due to its highly varied nature. PM is composed of different components, each with varying toxic effects. In particular, different particle sizes has been related to different toxic effects. This gives rise to the need in studying the ambient size distribution of OP. Apart from that, particle size affects the location of deposition in the respiratory system. This study determined the ambient size distribution of OP by the collection filter samples of different size ranges through the use of a Micro-orifice uniform deposit impactors (MOUDI), and determined the particle’s oxidative potential (OP) via the dithiothreitol assay (OP-DTT). Apart from the OP, the size distribution of the chemical components (elemental, ionic, and carbonaceous) were determined to elucidate any underlying mechanisms that might explain the observed OP values. Lastly, the deposition fractions for two age groups (adults and children) under different physical states (resting or doing a heavy activity) were determined by employing the Multi Path Particle Dosimetry (MPPD) model. The OP-DTT activity of was found to exhibit a bimodal distribution, usually peaking in the smaller size range around 0.18-0.56µm. Correlation analysis showed that the OP-DTT values were influenced by the OC, some transition metals (V, Mn, Fe, Ni, and Cu), and sulfate. In general, coarse mode particles were observed to contribute more at the head region while the accumulation mode particles contribute more at the tracheobronchial and pulmonary region. The OP deposition at the pulmonary region were higher for children compared to the adults, showing that they are at higher risk. Under physical exertion, adults showed an increase in OP deposition in the pulmonary region, which is in contrast to the decrease experienced children in the same region. This shows that adults experience an increased risk when exposed to toxic particles while they are doing physical work.