Levels of heavy metal concentration in leachate, borehole, and spring water in areas surrounding Kiteezi Landfill, Wakiso District, Uganda

Abstract

Rapid urbanization in developing countries has led to challenges in municipal solid waste management, including inadequate disposal in overflowing landfills lacking modern containment infrastructure. This results in uncontrolled leachate discharges that can pollute surrounding water resources by infiltrating shallow aquifers and surface waters. The Kiteezi landfill in Wakiso, Uganda exemplifies this issue. With increasing waste loads andan aged and defunct drainage system, heavy metal contamination of nearby springs and boreholes now poses major public health risks for villagers who depend on these supplies. This study aimed to provide a rigorous quantitative assessment of heavy metal concentrations in water sources in the Kiteezi region to guide mitigation strategies. Methods: We carried out sampling and laboratory analysis for heavy metals of 10landfill leachates, 15 boreholes, and 28 spring waters across six nearby villages (Lusanja, Kiteezi, Kabaga, Kabwoke, Kitetika, Nameere) within a 5 km radius. Concentrations of 10 heavy metals (lead, chromium, manganese, iron, copper, nickel, cobalt, cadmium, zinc, and arsenic) were determined using atomic absorption spectroscopy. The concentration of heavy metals in leachate samples was compared against NEMA effluent discharge guidelines. Concentrations of heavy metals in water samples were compared to WHO, USEPA, and Ugandan/ East African portable water quality standards. The spatial analysis examined distance trends indicative of leachate contamination gradients. Results: The leachate contained a median concentration of copper of 0.02mg/L (IQR: 0.01-0.03 mg/L), iron 1.73 mg/L (IQR: 1.17-3.48mg/L), manganese 0.81 Mg/L (IQR: 0.79-0.85 mg/L), nickel 0.08 (IQR: 0.08-0.12mg/L) and zinc 0.17 (IQR: 0.13-0.19mg/L) with concentrations within the NEMA regulatory standard for effluent discharge. The median lead concentration in leachate (0.12mg/L (IQR: 0.08-0.31mg/L) exceeded regulatory limits of 0.1mg/L. In the water samples, the median concentration of heavy metals was: cobalt 0.01mg/L (IQR: 0.005-0.007mg/L), copper 0.042mg/L (IQR: 0.009-0.067mg/L), iron 0.072mg/L (IQR: 0.028-0.190mg/L) and zinc 0.008mg/L (IQR: 0.003-0.018mg/L). However, their concentrations were within the acceptable limits of the WHO and Uganda/ East African standards (US EAS 12:2014) for portable water. Chromium and manganese had the highest concentrations; 0.36mg/L (IQR: 0.32-0.61mg/L), 0.278mg/L (IQR: 0.126-0.565mg/L), and 0.072mg/L (IQR: 0.028-0.19mg/L), respectively, with both above drinking water standards. Cadmium, lead, cobalt, and arsenic were neither detected in the borehole nor spring water and their concentrations were below the detectable limit. The average concentrations of chromium, copper, manganese, and nickel were higher in spring water than in borehole water while the average concentration of zinc and iron were higher in borehole water than in spring water. Approximately, 86% and 72% of the water samples had concentrations exceeding the safe levels of the WHO and EAS standards for chromium and manganese respectively. The concentration of zinc and iron was higher in borehole water than in spring water (p<0.001 and P=0.014, respectively) while the chromium concentration was higher in spring water than in borehole water (P= 0.047). Conclusion: This study confirmed the presence of heavy metals in the leachate at the Kiteezi landfill and the water sources in areas surrounding the landfill. Lead had the highest concentration in the leachate and was above the recommended NEMA acceptable limits. Chromium and manganese had the highest concentrations in the water and their average concentration was above the acceptable limits. Although the median iron concentration in water was within the stipulated limits, the concentration in borehole water was above the standards and there were sporadic occurrences of concentrations above the acceptable limits.