Impact of anthropogenic activities affecting the water quality of Umhlathuze River in KwaZulu Natal

Abstract

uMhlathuze River and its three main tributaries experiences various anthropogenic activities including agriculture, urbanization and industrialization before forming an estuary with the Indian Ocean. This River which is in the northern part of KwaZulu-Natal, South Africa supports a rapidly growing agricultural, domestic and industrial community. The comprehensive study was aimed to assess the potential impact of these anthropogenic activities over a 12-months period in 2023/4. The study showed that elementary levels were mostly within the permissible limits along uMhlathuze River, but the impact of anthropogenic activities along its tributaries was evident. Chlorides ranged between 400 and 655 mg/L along the Mholweni tributary during the rainy season while Na, Mg and Ca were also consistently above permissible limits along Mholweni and Ntambanana tributaries. Among non-toxic trace elements, only Fe exceeded its health-based precautional value during the rainy season for all sites. Trace toxic metal levels were also within permissible limits. Hg was only detected along the tributaries in the 0.017 - 0.399 µg L-1 range. The source of elevated levels of parameters along the tributaries was linked to quarry and agricultural activities and the wastewater effluents and urban runoff. The WQI values were in the 10.7 - 36.1 range implying the river water could be classified as good to excellent. The possibility of using these waters for agricultural purposes was assessed by calculating the Sodium Adsorption Ratio (SAR). The SAR results of the present study ranged from 29.5 to 76.3 which indicated that the water from the three tributaries (NTA, MH and EM) was unsuitable for irrigation. A health risk assessment identified that the river water was safe for domestic use to adults but infants and children were more likely to develop non-carcinogenic effects with HI values of 1.07 - 3.28. The ILCR values ranged between 1.20 and 9.93 indicating that consumption of unprocessed water from UMhlathuze and its tributaries will result in carcinogenic effects over one’s lifetime with infants and children affected most.