Reactive oxygen species (ROS) activity of fine particulate matter health impacts in Addis Ababa, Ethiopia

Abstract

Previous studies in Addis Ababa, Ethiopia, focused on PM characteristics and sources, but PM's biological activity in this area has not been adequately investigated. In this study, cellular and acellular ROS activities were measured to assess PM toxicity. PM2.5 samples in Addis Ababa were collected from November 2015 to November 2016 and their chemical composition was analyzed (organic and elemental carbon (OC/EC), ions, elements, and organic molecular markers). PM-induced ROS activity was measured in vitro in alveolar macrophage cells and using the acellular DTT assay. PM2.5 in Addis Ababa primarily consisted of primary pollutants (e.g., EC, water-insoluble OC). Annual average cellular ROS activities (±SD) were 46.5 ± 15.5 μg Zymosan/m3 and 995 ± 403 μg Zymosan/mg PM (normalized to air volume and PM2.5 mass, respectively), with no clear seasonal variations. The annual average DTT consumption rates (±SD) were 2.35 ± 0.83 nmol/min/m3 and 51.9 ± 17.6 nmol/min/mg PM, respectively, and were also similar throughout the year. Only the monthly air volume-based ROS activity had a similar trend to monthly mass concentration. Compared to other major cities worldwide, Addis Ababa PM2.5 had much lower ROS activity with no strong seasonal trends, paralleling the lack of seasonal changes in PM composition and sources. Poor correlations were observed between ROS activity and all components except mobile source tracers. This difference might be due to lower secondary aerosol content in PM2.5 in Addis Ababa than in other cities.