Metal retention potential of sediment and water quality in the Mooi River, South Africa

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The potential metal retention by sediments along the Mooi River and connected streams in the vicin - ity of Potchefstroom, South Africa, was evaluated using the four-stage sequential extraction proce - dure. The sediments were characterized using XRD, XRF and FTIR techniques. The physico-chemical parameters and heavy metals content of water were also measured to evaluate their impact on water quality and fitness for human consumption. The highest percentages of Fe, total Cr and Mg (83.46, 27.43, and 88.83%, respectively) were predominantly associated with the residual fraction of the sedi - ments. Elements such as Ca and Mn were mostly bound to the exchangeable fraction of the sediments. Association of Fe, total Cr and Mg with the residual fraction as predicted by speciation calculations suggests that these metals are strongly bound to the sediments and therefore less susceptible to cause pollution. The mobility order of the heavy metals in the sediments samples was Ca > Mn > Mg > Fe > Cr. For the first time the implication of organic matter in the sediments along the Mooi River on the retention of metals was investigated and it was found that organic matter occurring in various concentrations in these sediments, contained binding groups such as C–O, C–C=C, O–H and =C–H much likely to contribute to the retention of metals in the exchangeable fraction of the sediments. The amount of inorganic pollutants in water was found to basically decrease moving downstream, but the water quality remained unfit for human consumption at most of the sampling points