Bakyayita et al. 2019 — Trace metals in Lake Victoria basin groundwater and surface water, Uganda
This study assessed levels, speciation, and toxicity of selected trace metals in shallow groundwater, surface runoff, surface water, landfill leachate, and wastewater in subcatchment areas of the Lake Victoria basin, Uganda. Shallow groundwater was acidic (pH below 6.5). Some surface water samples contained iron, chromium, aluminium, and manganese above guideline values. Speciation modelling showed 74% of metal ions in surface water were bound to dissolved organic matter, while in landfill leachates the dominant species were metal hydroxides or fulvic-acid complexes. Risk analysis using the Swedish EPA framework found 30-76% of surface water sample sites showed varied negative-effects risks. Bio-met modelling indicated potential toxicity from Cu2+, Ni2+, Zn2+, and Pb2+ in 15.3-30.8% of surface water and 8.3-62.5% of groundwater samples.
Key numbers
pH of shallow groundwater: below 6.5 (acidic). Surface water: Fe, Cr, Al, Mn above guideline values at some sites. Speciation: 74% of metal ions in surface water bound to dissolved organic matter; in landfill leachates, dominant species were metal hydroxides or fulvic-acid complexes. Risk: 30-76% of sample sites (surface water) showed varied risks from high to increased per Swedish EPA assessment. ICP-MS instrument LOD: 0.002 ppm for Cd, 0.009 ppm for Pb. Surface water sampling: June 2014 and February 2015; groundwater: four annual samples March 2012 to February 2015. WHO guidelines, Ugandan standards, Canadian guidelines, and Swedish EPA used for assessment.
Methods (brief)
ICP-MS (PerkinElmer Elan 9000, 2007) for trace and major elements in acidified filtered water samples; Shimadzu TOC-5000 for DOC; leachate digested using wet acid digestion; speciation modelling using geochemical code; Bio-met tool for bioavailability-based toxicity risk assessment.
Implications
Certification: environmental context for supply chain water quality in East Africa; relevant to understanding groundwater quality inputs to agricultural irrigation.
Courses: useful case study for trace metal speciation in freshwater systems and the application of multiple risk assessment frameworks.
App: not applicable to food-matrix contamination profiling.