3.03.P–ThFr16 - Metal Pollution in Cape Town’s Urban Rivers: Spotlight on the Salt River Catchment

Abstract

The Salt River is a major urban catchment in Cape Town, South Africa, with two main tributaries, the Liesbeek and Black Rivers, covering large sections of Cape Town’s Southern suburbs. The Salt River enters the ocean at Table Bay. A multitude of pollution sources are found along the banks of these rivers, including industries, houses, sewage treatment plants, golf courses and informal settlements. This study investigated the spatial and temporal distribution of metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn), in the Salt River catchment through comparison of recent data (2022) with previous unpublished data (2006), comparison of wet and dry seasons and comparison of selected sampling stations. Five replicates of water and sediment samples were collected at each of the selected sampling stations, during two sampling occasions (wet and dry seasons 2022). Sample preparation and metal analysis was done using nitric acid digestion and an ICP-MS. Results showed that sections of both the Liesbeek and Black Rivers, as well as the single Salt River station, are heavily polluted with metals. Metals in water samples that exceeded the acceptable target quality range and fell within the moderate, large and critical impact categories were Al, Cr, Cu, Fe and Mn they are the categories as set in the new South African Water. Al, Cu, Fe, Mn and Zn in sediments were above the permitted set of guidelines as recommended by Canadian interim sediment quality guidelines. Results also showed that metal levels have significantly increased since 2006 due to increases in land use. Metal concentrations were also generally higher during the dry season of 2006, most likely due to reduced water flow and slower currents, but conversely higher during the wet season of 2022, most likely due to increased waste runoff inflow. The Salt River itself has proven difficult to study as it is entirely canalized, which indicates that potentially high loads of polluted sediment are carried straight to the lagoon. This study will form an important basis for further studies on the impacts of aquatic pollution on freshwater, coastal and marine biota. This research identified the need for continual monitoring of metal pollution in urban rivers to mitigate environmental and public risks, particularly in the Salt River catchment.
 

Author(s)

Presenter: Zikhona, Menze

Authors: 

Zikhona Menze Cape Peninsula University of Technology (CPUT) United States      James Odendaal Cape Peninsula University of Technology (CPUT) United States      Rashieda Toefy Cape Peninsula University of Technology (CPUT) South Africa
Reinette Snyman Cape Peninsula University of Technology (CPUT) United States