Heavy Metal Contamination and Ecological Risk Assessment of Soils Around Mzedi Municipal Dumpsite, Blantyre, Malawi: Implications for Food Safety in Subsistence Farming Areas

Abstract

Uncontrolled disposal of municipal solid waste is a growing environmental concern in developing countries, contributing to heavy metal accumulation in surrounding soils and water. This study assessed the concentrations, spatial distribution, and ecological risks of heavy metals around the Mzedi municipal dumpsite in Blantyre, Malawi. Composite soil samples were collected at 0 m, 50 m, 250 m, 400 m, and 650 m from the dumpsite, while surface water samples were taken from a nearby stream receiving runoff. Samples were analyzed for cadmium (Cd), zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), lead (Pb), and cobalt (Co) using atomic absorption spectrophotometry. Contamination and risk levels were evaluated using the Contamination Factor (CF), Geo-accumulation Index (Igeo), Enrichment Factor (EF), and Potential Ecological Risk Index (PERI). Soil metal concentrations decreased with distance from the dumpsite in the order Fe > Mn > Zn > Cu > Pb > Cd > Co. Cadmium exhibited the highest contamination levels, with CF (70.00), Igeo (5.54), and EF (19.17) at 0 m indicating extremely polluted conditions and severe anthropogenic enrichment. PERI values ranged from 2,181 at 0 m to 117 at 650 m, shifting from very high to low ecological risk. Cadmium contributed > 96% of the total ecological risk, confirming it the dominant contributor to ecological risk. In surface water, Cd (0.006–0.008 mg/L) and Pb (0.025–0.030 mg/L) exceeded WHO drinking water guidelines, confirming leachate-driven contamination of the adjacent stream. While crop metal concentrations were not directly measured, the elevated soil cadmium levels indicate potential for plant uptake and possible human exposure. However, without direct crop analysis, we cannot confirm the extent of food chain transfer, quantify dietary exposure, or assess compliance with food safety standards. This highlights the critical need for targeted crop monitoring studies to validate the inferred human health risks. This study provides the first comprehensive quantitative assessment of ecological risk at the Mzedi dumpsite using multiple contamination indices and robust statistical analysis. The findings support precautionary management measures, including restrictions on farming directly on the dumpsite, upgrading of waste disposal infrastructure, and community awareness programs.