Oxidative potential of atmospheric particulate matter collected in low-income urban settlements in South Africa

Abstract

Health-related impacts e.g. respiratory and cardiovascular morbidity and mortality, associated with exposure to atmospheric particulate matter (PM) are globally considered important and are not completely understood. Oxidative potential (OP), defined as a measure of the capacity of PM to oxidise target molecules, has been previously proposed as an alternative relevant biological metric in health studies to better quantify toxicological responses associated with PM exposure than aerosol mass alone. Several methods are currently used to assess the oxidative capacity of PM. In this study, the dithiothreitol (DTT) assay was used, which is the most commonly used technique to estimate OP. This assessment is easy-to-operate, low-cost, effective and reproducible. The first step was to modify the DTT methodology based on previous applications, which entailed choosing an appropriate extraction procedure and -setup. The redox activity of size-resolved PM samples collected in three low-income urban settlements in South Africa, i.e. Jouberton, KwaZamokuhle and Zamdela was evaluated and related to their chemical composition through correlation analysis. Furthermore, it was attempted to determine seasonal variations of DTT redox activity through normalisation according to PM mass (DTTm) and sampled volume (DTTv) for outdoor and indoor environments. The results indicated higher redox activity for the finest (<1 μm) particles compared to the coarser particulates (1-10 μm) for both outdoor and indoor environments. DTT redox activity of PM, especially, in the PM1-10 particle size fraction, had strong correlations with elemental (EC) and organic carbon (OC), as well as trace elements and water-soluble inorganic species for outdoor and indoor samples. Possible atmospheric aerosol emission sources suggested from these correlations include primary emissions from domestic- and open biomass burning, vehicles and industrial activities, as well as secondary particle formation (e.g. sulphate).