Phytoextraction of anthropogenic heavy metal contamination of the Blesbokspruit wetland: Potential of wetland macrophytes

Abstract

Blesbokspruit wetland is one of the least conserved ecosystems in the Southern Africa region with active and latent threats of anthropogenic contamination stretching over decades of mining wastewater discharge, agricultural run-off, and a consistent influx of untreated sewage. This study provides an insight into the present-day spatial distribution of heavy metal contamination and the role of localised macrophytes in their phytoremediation. With exception of the first sampling point, the concentration of heavy metals in water samples throughout the wetland was within limits however findings from sediment samples were the inverse. The concentrations of Chromium and Nickel significantly exceeded both effect range low (ERL) and effect range medium (ERM) limits (250-430 mg/Kg and 73-151 mg/Kg respectively) as set out by international sediment quality guidelines. Emergent- Phragmites australis, Typha capensis, and free-flowing-Eichhornia crassipes macrophytes, which are naturally localised to the wetland were found to have varying bioaccumulation potential for different heavy metals; Bioconcentration of heavy metals in emergent macrophytes was relatively low especially for Nickel and Chromium compared to free-flowing macrophytes. E. crassipes accumulated significant amounts of the heavy metals with root concentrations of up to 17.23, 116.6, 330.5, and 342.9 mg/Kg for Arsenic, Lead, Nickel, and Chromium respectively. The emergent macrophytes were however found to bioconcentrate Arsenic up to 1.15 L/Kg (T. capensis) and 9.9 L/Kg (P. Australis) at sites 4 and 5 respectively. Findings with regards to bioconcentration especially of the E. crassipes, validate recommendations for the utilization of hyperaccumulating macrophytes for the natural recovery of these heavy metals towards alleviating the anthropogenic stress on this valuable ecosystem.