Heavy Metal Partitioning in Sediments from Rivers Flowing Through Coal Fields in Mpumalanga, South Africa

The association of elements Cd, Co, Cr, Fe, Mn, Pb, Ti, and V with various geochemical phasesinthesedimentsfromtheOlifants, KleinOlifants, Wilgeriversandatributaryof the Olifants River was studied using a four-step sequential extraction scheme. By employing enrichment factors, these elements were found to be contaminating the sediments. Sequential extraction enabled partitioning of the metals into exchangeable, reducible, oxidizable, and residual fractions. Most of the elementswere found to exist in the residual fraction, characterized by stable compounds. Application of risk assessment code to the exchangeable fraction revealed that most of the elements posed amediumrisk to aquatic life, withthe exceptionofCo, Pb, andMn, whichwere classifiedintothe high-riskcategory. Non-residual/ more bioavailable fractions were examined using statistics. Correlation analysis was employed to understand the interaction between the more bioavailable fractionsofmetalswiththereduciblephaseconsistingofoxidesofFeandMn. Theseoxides contribute to the adsorption of trace metals onto sediments. Co, V, Pb, Cr, and Cd in the reducible fraction were found to be associated with Fe-oxides, while V, Cr, and Ti were associated with Mn-oxides, as indicated by significantly high correlation coefficients. Throughclusterandfactoranalysis threeanthropogenicactivitiesassociatedwithmining and use of coal and iron and steelmanufacturing were found to be contributingmetals to the sediments.