Assessment of trace metal contamination in overbank sediments of the Witbank Coalfield, South Africa

Abstract

Overbank sediments are a significant sink for trace metals (TMs) and, thus, may represent an important secondary source of TMs in industrial environments. The current study (i) assessed the degree of TM contamination in overbank sediments along the Blesbokspruit River (located in the Witbank Coalfield in South Africa) using enrichment factors (EFs); and (ii) determined potential sources of TM contamination using log-ratio-transformed data as inputs to factor analysis (FA). Overbank sediments along the study site were characterized by no to minor enrichment of Al, Ni, Cu, Zn and Pb; no to moderate enrichment of Fe and Cr; and no to moderately severe enrichment of Mn and Cd. The FA revealed three main factors: F1 (loaded mainly by Zn and Ni), F2 (loaded mainly by Pb and Cu) and F3 (loaded mainly by Cr). With the exception of samples along the main roadway, Zn and Ni which loaded F1 appeared largely derived from acid mine drainage (AMD) linked to coal mining in the study site, while F2 (loaded by Cu and Pb) and F3 (loaded by Cr) could be linked to additional sources, such as industrial wastewater and ferrochrome processing, respectively. This study highlights the importance of monitoring AMD and industrial wastes and emissions in the study area to minimize the potential threat of TMs to environmental and human health.