Abstract:
Wetlands are one of the most crucial resources since they provide diverse benefits to the
ecosystem. Therefore, South Africa has put in place policies and guidelines to safeguard these
valuable resources. This study was conducted to evaluate water quality and the potential
ecological risk due to trace metals in sediments across wetlands in Limpopo Province. The
samples' physicochemical parameters were tested in the field and the laboratory. All the
instruments used to test the physicochemical parameters of the water samples were calibrated
first and all the measurements were done in triplicate. The water and sediments samples were
digested following the method recommended by US EPA 3015 for aqueous samples and 3050
for sediments samples, respectively. This was done to dissolve the metals that cannot are
insoluble in neutral pH but soluble in acidic pH. For trace metals, the digested samples were
analysed using inductively coupled plasma mass spectrometry (ICP-MS). Sediment quality
guidelines standards for the protection of aquatic life were studied and compared with the
threshold effect levels (TEL) and probable effect levels (PEL) as well as effect range-low (ERL)
and effect range median (ERM). The potential ecological risk index (PERI) for sediment was
studied using indices. The removal efficiency of pollutants from one of the wetlands was
calculated to check if the wetland still performs its function. Most concentrations for both the
physicochemical parameters and trace metals were within the recommended standards for
irrigation and aquatic ecosystem by the Department of Water and Sanitation (DWS) standards
formerly referred to as DWAF. However, the dissolved oxygen levels recorded were below the
World Health Organisation guideline standard (5 mg/L) in the water of all sampled sites as it
reported to be ranged between 0.773±0.155 (W4) to 3.88±1.00 mg/L (W10). In addition, Iron, and
manganese exceeded the DWAF irrigation and aquatic protection threshold limit in all wetlands.
Fe and Mn varied between W8-12973.62 62 μg/L and W1-77.42 62 μg/L Sediment quality
guidelines standards presented levels below the threshold effect levels and effect range-low in
most samples. However, few samples presented levels above the threshold effect levels and
effect range-low but below the probable effect levels and the effect range median. Most of the
sites presented low levels of risk index (RI) values, excluding W3 and W12 which presented a
very high risk index (RI) value. The contamination factor values of Cr levels recorded at some
sites (W3, W5, W9, W11, W12, W15, and W16), presented extremely high levels greater than
CF>32 of toxicity to aquatic biota. Level of contamination (CD) values presented extremely high
risk greater than 32 of contamination to 46.67% of sites.
Phangami wetland was found to be efficient in reducing the pollution burden of wastewater
disposed into the wetlands and recorded acceptable reduction efficiencies for most of the metals
recorded.
