Oxidative Potential Dependence on the Chemical Composition of PM2.5 and PM10 Samples

Epidemiological and toxicological studies have shown that the exposure to ambient particulate matter (PM) leads to adverse health effects in humans. The most accredited pathophysiological mechanisms involve several oxidative mechanisms leading to high concentrations of reactive oxygen species (ROS) in vivo. Such an imbalance toward a ROS excess translates into numerous health outcomes. Two common acellular techniques based on low-cost spectrophotometric UV-Vis measurements were used in this study to assess the oxidative potential (OP) of PM10 and PM2.5 samples. One is the dithiothreitol (DTT) assay, where DTT acts as a surrogate for biological reducing agents owing to its two sulfhydryl groups. The other assay is based on the ascorbic acid (AA), that is a physiologically antioxidant found in lung fluid. In order to investigate the association of the measured oxidative responses with the PM chemical composition, inorganic and organic ions, metals, organic and elemental carbon were quantified in simultaneously collected PM2.5 and PM10 samples. The DTT and AA assays provided DTT-OP and AA-OP responses very similar in mean values and variability range, but different in association with chemical species and seasonal variation. More specifically, the AA-OP was strongly positively correlated with the main tracers of traffic and/or combustion emissions in Autumn-Winter (AW). In Sprin-Summer (SS) AA-OP was mainly correlated with species related with secondary aerosol and resuspended soil from vehicular traffic and/or long-range transport of Sahara dust. The DTT-OP of AW samples was well correlated with tracers of the resuspended reacted dust source, vehicle-related metals, and EC and OC associated with combustion sources. Conversely, in SS the DTT-OP of SS was correlated only with NH4+,Cu, EC and POC. In conclusion, our study has highlighted the differences between the responses of the two commonly utilized DTT and AA assays to assess aerosol OP in both PM10 and PM2.5. Moreover, paper’s results have confirmed that the toxicity of ambient PM is a multifaceted phenomenon caused by a multiplicity of redox-active species and depending on the activity and concentration level of the individual components as well as on possible interaction/synergic effects.