Abstract
Mokolo River supplies water to the Mokolo Dam, which serves as the main source of water supply for the Waterberg region in the Limpopo Province, South Africa. However, the state of the river is of great concern due to the anthropogenic activities taking place in its proximity. Mokolo River is likely to be polluted by municipal and agricultural sewage works, as well as atmospheric deposition of mine dust and emissions from coal-fuelled power stations. This could lead to the river being contaminated with potentially toxic elements (PTEs) like mercury (Hg) and other contaminants, thus affecting the water quality of the river and its aquatic organisms. Mercury in the aquatic system is of great concern due to its toxicity and poses a threat to both human health and the ecosystem. As such, determining the levels of Hg in the Mokolo River is crucial in assessing the state of the river. However, determining the total concentration alone does not give enough information about the health risks associated with Hg, thus chemical speciation serves as a vital tool for assessing water quality since the actual toxicity, bioaccumulation and reactivity of Hg depends on the chemical forms present. The aim of this study was to quantify total Hg and speciate the levels of Hg(II) and methyl mercury (MeHg(I)) in sediment samples collected from Mokolo River in different seasons. Water and sediment samples were collected from ten different sampling sites based on accessibility. Microwave-assisted digestion and ultrasonic extraction methods were used to achieve a safe, simple and fast method for quantification of total Hg and Hg species in sediment samples, respectively. The total concentration of Hg in water was determined by inductively coupled plasma-mass spectrometry (ICP-MS). The method was validated by spiking the water samples with Hg concentrations at 1X limit of quantification (LOQ) and 10XLOQ levels and calculating the percentage recoveries of Hg. Total Hg in sediment samples was quantified by ICP-MS. The accuracy of the method was validated by the analysis of the standard reference material of sediment (SRM2709a) and percentage recovery of 90% was obtained. The total concentrations of Hg ranged from 40.3 to 64.1 ng/g in and 44.6 to 98.6 ng/g in the high and low flow seasons, respectively...
M.Sc. (Chemistry)