Oxidative potential of particulate matter collected at sites that differ in local emission sources

摘要

Background: The capacity of particulate matter (PM) to oxidise target molecules, defined as its oxidative potential (OP), has been proposed as a biologically more relevant metric than PM mass . Different assays exist for measuring OP and little is known about how different PM characteristics or sources contribute to the different measures of OP. Aim: To assess the OP of PM collected at sites with different local emission sources and to study the correlation with chemical composition for different measurement methods for OP. Methods: Within the framework of the RAPTES study (Risks of Airborne Particles-a Toxicological Epidemiological hybrid Study) PM2.5 and PM10 was sampled at 5 different sites: an underground train station, an animal farm, 2 different traffic sites and an urban background site in the Netherlands. Three a-cellular assays; dithiothreitol (OPDTT), electron spin resonance (OPESR) of hydroxyl radical generation, and ascorbate acid depletion (OPAA) were used to characterise the OP of PM. Results: By far the highest OP was observed at the underground, where OP of PM10 was 30 (OPDTT),) to over 600 (OPESR) times higher compared to the urban background location. For the outdoor sites, samples from the farm showed significantly higher OPDTT compared to the urban background and significantly lower OPESR and OPAA. Samples from the continuous traffic site showed significantly higher OP compared to the urban background for all assays. Contrasts in OP between sites were generally larger than for PM mass and NO2, but similar to contrasts observed for EC and traffic-related metals (e.g. Cu, Fe, Sb). OPDTT was highly correlated with PM mass (R 0.75-0.86), whereas OPESR and OPAA were highly correlated with EC, Cu, Fe, Sb and Mn (R 0.47-0.80). Conclusions: The OP of PM was highly elevated at an underground train station compared to outdoor locations. For the outdoor locations, the highest OP was observed along a highway with continuous traffic. Contrasts between sites as well as correlations with chemical characteristics depended on the specific OP assay used.