Characterization of the oxidative potential of water-soluble fraction of atmospheric aerosol in an urban background site in southern Italy

Several studies point out oxidative potential (OP) as a quantitative indicator of multiple particulate matter (PM) health effects, since OP of ambient particles causes high concentrations of reactive oxygen species (ROS). ROS concentrations, in excess of the antioxidant capacity to neutralize them, lead to oxidation of other cellular components, which eventually translates into numerous health consequences. Indeed, although the human body is capable of settle with ROS, diseases can overcome or weaken the defense mechanisms. In that case, ROS can generate a series of damaging events. Oxidative potential (OP) is defined as a measure of the capacity of PM to oxidize target molecules. It has been proposed as an indicator related to biological reactions to PM exposures and thus could be more revealing than mass concentration alone. Over the years, several methods for testing OP have been developed. In this work, we evaluated the OP of the water-soluble fraction of PM2.5 and PM10 using the a-cellular DTT (dithiothreitol) test. The consumption of dithiothreitol (DTT) is based on the ability of redox active compounds to transfer electrons from DTT to oxygen. Briefly, aliquots of PM2.5 and PM10 water extracts were incubated with DTT. The reaction was stopped at designated time points, adding 5,5′-Dithiobis(2-nitrobenzoic acid) (DTNB). The absorbance at 412 nm was recorded and the rate of DTT consumption (DTT, pmol/min) was determined from the slope and intercept of linear regression of measured absorbance versus time. Three replicates were done, for each sample, and the standard deviation among the replicates was taken as uncertainty of the measured DTT activity. Daily (from 15/11/2016 to 15/11/2017) PM2.5 and PM10 samples were simultaneously collected, on quartz substrates, using a dual channel low-volume (2.3 m3/h) sampler (SWAM, Fai Instruments). The samples were collected at the Environmental-Climate Observatory of Lecce, regional station of the Global Atmosphere Watch (GAW-WMO) network, that could be considered an urban background station located at 4 km from the town of Lecce and between 30 km and 80 km from large industrial sites of Brindisi and Taranto. Finally, seasonal variability of measured DTT activity was investigated and correlated with aerosol concentrations observed on collected samples.