Quantifying the oxidative potential of aerosols in low-income urban areas in South Africa

Health impacts associated with exposure to atmospheric aerosols are of global concern and are not completely understood. In addition, health studies are, especially, complicated in developing countries such as South Africa. Oxidative potential (OP), defined as a measure of the capacity of aerosols to oxidise target molecules, has been proposed as a viable alternative relevant biological metric to better quantify toxicological responses related to atmospheric aerosol exposure in health studies. The dithiothreitol (DTT) assay is the most commonly used method to determine OP of aerosols, which was used in this study to quantify the OP of outdoor and indoor atmospheric particulates collected at three low-income settlements in South Africa. This technique is easy-to-operate, low-cost, effective and reproducible. The DTT methodology had to be modified according to previous applications, which required choosing a suitable extraction procedure and -setup. The redox activity of size-resolved sampled aerosols was evaluated and related to their chemical composition with correlation analysis. The seasonal variations of DTT redox activity were established by normalizing in terms of aerosol mass and sampled volume for indoor and outdoor particulate samples. Higher redox activity was determined for the smallest aerosols (aerodynamic diameter <1 μm) compared to the larger particulates (aerodynamic diameter between 1 and 10 μm) in both environments. DTT redox activity correlated strongly with elemental- and organic carbon, as well as trace elements and water-soluble inorganic species. These correlations revealed toxic effects of sources of atmospheric aerosols in these settlements, which included domestic- and open biomass burning, vehicles and industrial activities. The DTT method was successfully applied in this study and could be used in other data scarce regions that are difficult to access.