Indoor/Outdoor particulate matter (respirable dust) and respirable crystalline silica source tracking in households located proximal to gold mine tailings in Johannesburg, South Africa

Introduction: This study aimed to investigate the concentration of Respirable Crystalline Silica (RCS) and respirable dust, Particulate matters (PM4) concentration in samples measured indoors and outdoors of the nine(9) selected households located proximal to gold mine tailings in Riverlea, Johannesburg. Materials and methods: Sampling locations were separated according to grids, based on distance from the tailings; A (<500 m from the dump), B (>500m<1 km) and C (1 km-3 km). Three households were selected from each grid zone to measure indoor and outdoor PM4 samples continuously over 24 h using GilAir constant sampling pumps. Samples were collected during dry and wet seasons, and respirable crystalline silica in PM4 samples were analysed by an X-ray diffraction method. Results: The mean indoor and outdoor PM4 mass concentrations ranged from 2.02±0.02 µg/m3 to 2.26±0.02 µg/m3, respectively. The dry season mean for PM4 mass concentrations were higher than the wet season PM4 mass concentrations in all zones. The pairwise comparison of PM4 mass concentration for dry and wet seasons revealed no statistically significant difference (p<0.05). The dry season means the indoor/outdoor ratio was greater than one across all zones, suggesting indoor activities as the primary source of PM. In both seasons, the mean indoor and outdoor RCS ranged from 0.02±0.01% to 0.06±0.03%. The mean indoor and outdoor 24 h RCS concentrations in both seasons were below the California Office of Environmental Health Hazard Assessment (OEHHA) defined 24 h ambient exposure threshold of 3 µg/m3. Conclusion: The study found that PM4 concentration was directly proportional to distance from the gold mine tailings. Using RCS as a signature chemical, we found a similar chemical composition in all samples collected in winter and dry season at varied distances. It is concluded that the gold mine tailings are the significant source of PM4 emissions. Therefore, further dust control measures needs to be implemented at the gold mine tailings.