A New Metric of Fine and Ultrafine PM Exposure: the Region-specific Oxidative Stress Index (SOS)

摘要

The current study provides a methodological framework for introducing refined exposure information into environment and health associations, by deriving a composite exposure metric we call "region specific oxidative stress index SOS". The latter takes into account the size specific mass deposited to region of the Human Respiratory Tract (HRT) as well as the size specific Reactive Oxygen Species (ROS) generating potential of PM. Based on the PM size specific oxidative potential and the deposition across the HRT, the SOS index is calculated as the product of the size specific mass deposited to the HRT region, multiplied by the oxidative potential of this size specific PM thus, we surmise that it is a more relevant metric for PM health associations. To investigate the feasibility of using this approach an extensive measurement campaign was carried out in a large Metropolitan area in Greece. PM size and number distributions were recorded in four sites. PM10, PM2.5, PM1 and UFPs samples were analyzed for oxidative potential by measuring ROS using the DTT protocol. Results showed that the fine particle concentration is higher in the city center than in the suburbs. The same is true for the oxidative potential especially for the smaller particles. Thus, the difference between actual exposure in the different monitoring sites for endpoints related to lower respiratory tract deposition and possibly translocation within the systemic circulation (e.g. cardiovascular disease, adverse pregnancy outcomes) might be up to 4 times higher than the one estimated by the respective differences in mass concentration. The SOS index proposed herein, could serve as a starting point for translating environmental information (PM measurements and ROS analysis) into an enhanced exposure metric; this could provide an intermediate advancement between existing concentration-response functions and a fully mechanistic assessment of PM associated mortality and morbidity.