1. Occupational Hygiene and Health Research Initiative (OHHRI), North-West University, Potchefstroom 2520, South Africa
2. Department of Physiology and Environmental Health, University of Limpopo, Sovenga 0727, South Africa
3. Environmental and Health Research Unit, South African Medical Research Council, Pretoria 0002, South Africa
4. Department of Geography, Geoinformatics and Meteorology, University of Pretoria, Pretoria 0001, South Africa