16. Oxidative Potential of Particulate Matter: A Prospective Measure to Assess PM Toxicity

It is now broadly accepted that particulate matter exposure can lead to multiple adverse health effects. The capability of airborne particulate matter (PM) to generate reactive oxygen species (ROS), known as “oxidative potential” (OP) is suggested to be one of the most relevant indicators of PM toxicity. Redox active chemical species in PM, of both inorganic and organic nature, facilitate ROS generation, causing oxidative damages, which are harmful for cells, ultimately leading to different chronic diseases. Therefore, OP has been proposed as a new additional metric for PM toxicity which is better associated with biological responses to PM exposures, thus could be more informative than particulate mass alone. However, the mechanisms of toxicity and its relation with the physico-chemical properties of PM are still largely unknown and need further research. Several chemical assays exist to assess the oxidative potential of PM. They differ from each other in sensitivity to the ROS generating chemical constituents of PM. The consumption of dithiothreitol (DTT), which is primarily based on the capability of redox active compounds to transfer electrons from DTT to oxygen, is used as the most widely applicable acellular method to assess the OP of PM. The potential of PM to deplete antioxidants such as glutathione, ascorbic acid and uric acid are a few of the other methods used to measure OP with respect to time. Another method, electron spin resonance (ESR) with 5,5-dimethylpyrroline-N-oxide (DMPO) as a spin trap, measures the ability of PM to induce hydroxyl radicals in the presence of H₂O₂. The current understanding of oxidative potential of PM, its analysis methods, along with its spatial distribution across the globe are presented here. Effect of various particle sizes, chemical composition, and nature of origin in exhibiting oxidative potential and its impact on health are additionally discussed.