Assessment of the Potential Ecological Risks of Heavy Metals in Soil and Water Around Lunzu Solid Waste Dumpsite

Abstract

The indiscriminate dumping of municipal solid waste in Malawi, particularly at Lunzu dumpsite in Blantyre, has raised significant environmental concerns due to the potential contamination of surrounding soils and water sources by heavy metals (HMs). This study assessed the concentrations, spatial distribution, and ecological risks of selected heavy metals, cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), iron (Fe), manganese (Mn), and cobalt (Co) in soil and groundwater around the dumpsite. Samples were collected at varying distances (0-250 m radius from the dumpsite) during both dry and wet seasons and analyzed using Flame Atomic Absorption Spectrophotometry (AAS). In soil, the highest concentrations were recorded at the dumpsite center during the dry season: Cd at 3.08 mg/kg, Cu at 316.18 mg/kg, and Pb at 80.00 mg/kg, exceeding the WHO and EU permissible limits. In the wet season, metal concentrations were lower but still elevated, with Cd at 2.77 mg/kg, Zn at 635.22 mg/kg, and Pb at 72.00 mg/kg. In water samples, the maximum concentrations during the dry season were Cd at 0.02 mg/L, Pb at 0.14 mg/L, and Fe at 1.56 mg/L, which exceeded WHO drinking water standards, particularly for cadmium and lead. Correlation analysis revealed strong positive relationships among most metals and soil organic carbon (SOC), suggesting common pollution sources and the role of organic matter in metal retention. Water samples also revealed elevated concentrations of cadmium and lead, with levels surpassing WHO, EU, and Malawi Bureau of Standards (MBS) guidelines, posing serious health risks to nearby communities. Contamination assessment indices like the contamination factor (CF), geo-accumulation index (Igeo), enrichment factor (EF), and potential ecological risk index (PERI) consistently identified cadmium and mercury as the most ecologically hazardous metals. The spatial trend showed a decline in metal concentrations with increasing distance from the dumpsite, confirming the dumpsite as the primary contamination source.