Assessing the influence of human activities on river health: a case for two South African rivers with differing pollutant sources

The impact of agricultural and anthropogenic activities can play a significant role in heavy metal precipitation and transport in water. Human activities along two rivers: the Palmiet and Sezela Rivers in KwaZulu-Natal, South Africa, have been classified and metal contamination (Cr, Cu, Pb and Zn) and mobility assessed using a range of factors including contamination and enrichment factors, pollution load indices and water quality parameters. The overall assessment of the Palmiet River, which is characterised by industrial zone (predominantly metal works), followed by residential areas and informal settlements shows significantly elevated metal concentrations with high mobility and bioavailability. In contrast, the Sezela River, characterised by agricultural activities and informal settlements, shows total metal concentrations that pose a limited-to-no threat to human health and very limited metal mobility. The overall environmental assessment indicates that both rivers show deterioration; the Palmiet River has been severely impacted by the type of industrial activity, whereas the Sezela River has been more impacted by agricultural activity. This study highlights the role of different anthropogenic activities on river health and the potential health implications with the associated metal mobility.