Assessment of trace metals contamination of surface water and sediment: A case study of Mvudi River, South Africa

Abstract

Trace metals contamination of rivers and sediments remains a global threat to biodiversity and humans. This study was carried out to assess the variation pattern in trace metals contamination in Mvudi River water and sediments for the period of January-June 2014. Metal concentrations were analyzed using an inductively-coupled plasma optical emission spectrometer after nitric acid digestion. A compliance study for the water samples was performed using the guidelines of the Department of Water Affairs and Forestry (DWAF) of South Africa and the World Health Organization (WHO). The National Oceanic and Atmospheric Administration (NOAA) sediment quality guidelines for marine and estuarine sediments and the Canadian Council of Ministers of the Environment sediment guidelines (CCME) for freshwater sediments were used to determine the possible toxic effects of the metals on aquatic organisms. pH (7.2-7.7) and conductivity (10.5-16.1 mS/m) values complied with DWAF and WHO standards for domestic water use. Turbidity values in nephelometric turbidity units (NTU) were in the range of 1.9-429 and exceeded the guideline values. The monthly average levels of trace metals in the water and sediments of Mvudi River were in the range of: Al (1.01-9.644 mg/L and 4296-5557 mg/kg), Cd (0.0003-0.002 mg/L and from below the detection limit to 2.19 mg/kg), Cr (0.015-0.357 mg/L and 44.23-149.52 mg/kg), Cu (0.024-0.185 mg/L and 13.22-1027 mg/kg), Fe (0.702-2.645 mg/L and 3840-6982 mg/kg), Mn (0.081-0.521 mg/L and 279-1638 mg/kg), Pb (0.002-0.042 mg/L and 1.775-4.157 mg/kg) and Zn (0.031-0.261 mg/L and 14.481-39.88 mg/kg). The average concentrations of Al, Cr, Fe, Mn and Pb in the water samples exceeded the recommended guidelines of DWAF and WHO for domestic water use. High concentrations of Al and Fe were determined in the sediment samples. Generally, the concentrations of Cd, Cr and Cu in the sediments exceeded the corresponding effect range low (ERL) values in the sediment quality guidelines and could have adverse effects on aquatic organisms in Mvudi River.