Abstract

According to the current understanding, the adverse health effects of particulate matter (PM) are produced by oxidative stress processes. Hence, the oxidative potential (OP) can be used as an exposure metric for more accurate approaches to the health response to ambient PM. This work explores the relationship between respiratory deposition of size-segregated PM and OP in the city of Santiago, Chile. Size-segregated PM samples were collected at an urban site using a Micro-Orifice Uniform Deposit Impactor (MOUDI) sampler. Dithiothreitol (DTT) loss rates were measured in aqueous PM extracts to estimate the OP for each sample. Size-segregated OP showed a bi-modal distribution with a maximum centered in the accumulation mode (0.18-3.2 mu m) and other in the coarse mode (3.2-18 mu m). The magnitude of the OP estimated in the accumulation mode was 2.9 +/- 0.8 and 2.3 +/- 0.6 times the magnitude of the OP estimated in the coarse and quasi-ultrafine mode, respectively. Respiratory deposition calculations indicated that PM3.2 (with diameter less than 3.2 mu m) dominated the OP lung deposition with contributions ranging from 65 to 94% in different areas of the human respiratory tract. This was due to the deposition efficiency and greater surface area of these fractions that allowed more efficient adsorption of active redox chemical species. These results may account for the greater negative impact on the lung health of the fine fractions of PM. The characterization of the OP respiratory deposition related to different fractions of PM, can result in adequate metrics to evaluate human exposure to PM and its possible health impacts.