Assessment of Heavy Metal Accumulation in Wastewater-Receiving Soil-Exotic and Indigenous Vegetable Systems and Its Potential Health Risks: A Case Study from Blantyre, Malawi.

Urban and peri-urban farmers in Malawi increasingly use treated and untreated wastewater for vegetable production, but little is known about the extent of heavy metal accumulation in both exotic and indigenous vegetables, particularly with respect to differences between edible tissues (leaves vs. stems). This study addresses this gap by measuring the concentrations of cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), and copper (Cu) in wastewater, soils, and six vegetables including three exotic and three indigenous irrigated with effluent from the Soche Wastewater Treatment Plant in Blantyre. Metal concentrations were determined using Atomic Absorption Spectrophotometry. Wastewater contained Zn (0.01 ± 0.001 mg/L) and Cu (0.02 ± 0.018 mg/L), both below World Health Organization (WHO) and Malawi Bureau of Standards (MBS) limits (Zn: 0.2 mg/L; Cu: 2 mg/L), while Cd, Cr, and Pb were below detection limit. In soils, Zn reached 56.4 ± 0.5 mg/kg, exceeding the WHO limit of 36 mg/kg; other metals remained within WHO permissible values. Vegetables showed species- and tissue-specific variation in metal accumulation: Cr reached 4.65 mg/kg in