Natural attenuation of mining pollutants in the transboundary Save River

• Published in: Physics and chemistry of the earth. Parts A/B/C 2011, Vol.36 (14-15), p.836-841
• Main Authors: Meck, M.L., Masamba, W.R.L., Atlhopheng, J., Ringrose, S.
• Format: Article
• Language: English
• Subjects: Attenuation; Costs; Dorowa; Ecological services; Ecosystems; Metal attenuation; Mining; Pollution abatement; Precipitation; Rivers; Save River; Sediments
• ISSN: 1474-7065; 1873-5193
• DOI: 10.1016/j.pce.2011.07.048

► We model metal activities using Visual Minteq to highlight ecosystem benefit. ► Attenuation is achieved through precipitation and deposition of solids onto sediment. ► Natural environment is protecting river water thus downstream users are shielded. ► Natural attenuation at Dorowa is a public good service. The objective of the study was to investigate the role played by the natural environment in protecting the transboundary Save River from the impacts of metals derived from phosphate mining at Dorowa. The study is a follow up study from a previous one that noted that there is natural attenuation at Dorowa. Water and sediment samples were collected in the Save River and the streams that drain the Dorowa dumps. Inductively coupled plasma mass spectrometry (ICP–MS) was used to analyze the cations (Na+, K+, Ca2+, Mg2+, Cu2+, Co2+, Fe2+, Ni2+, Zn2+, Pb2+, Sn2+, Mn2+, Cd2+) in the samples. Major anions Cl−, SO42- and NO3- were analyzed by standard chromatography whilst CO32- and HCO3- were determined by titration. pH was measured on site. Geochemical modeling of the water composition was conducted with Visual Minteq. The results show that natural attenuation is being achieved through precipitation of solids from the water and subsequent deposition onto the sediments. Six of the metals are almost completely precipitated (Cu 99.99%, Fe 99.39%, Ni 91.24%, Pb 99.87%, Sn 99.99% and Zn 88.66%). However Mn, Co and Cd remain in solution. Thus the natural environment is protecting the Save River which is a transboundary river from the impacts of mining through precipitation of the metals. Users downstream of Dorowa mine are therefore not being affected by mining pollution. This study demonstrates that besides being a legitimate and important user of water, the natural environment can also play a significant role in protecting water quality by attenuating metals naturally. By analyzing costs incurred in several places where alternative methods are employed to remediate metal related pollution the study concludes that natural remediation at Dorowa is saving the nation in environmental costs. Therefore the paper advocates for appreciation of the role that the natural environment plays in protecting ecosystems from the impact of human developments and environmental costs. Subsequently, this calls for recognition of natural environment’s role in water resources management for the sustenance of ecosystems and peoples livelihoods.