Metal Concentrations in Edible Leafy Vegetables and Their Potential Risk to Human Health

Leafy green vegetables provide important nutrients for human growth; however, human health is highly compromised through consumption of vegetables contaminated by heavy metals. Therefore, the study aimed to investigate the bioaccumulation of heavy metals in five different leafy green vegetables and soils and determine the human health risks that may arise from consuming those vegetables from Tonga town in Mpumalanga province, South Africa. Soils and five edible leafy vegetables (i.e., lettuce, cabbage, rape, pumpkin leaves, and spinach) were assessed for bio-concentration factor, daily intake of metals, health risk, and target hazard quotient across the study sites. The Si, K, Na, Ca, Mg, Al, and Fe concentrations were high in the soils. In general, vegetables exhibited elevated Ca, Fe, Si, Al, and Sr levels, although spinach had high Na concentrations. The bioconcentration factor showed the following trends: Mg > B > Si > V for trace metals and Cr > Co > Mn > Ni > B for heavy metals in lettuce, spinach, and pumpkin leaves. The human risk index for all vegetables showed that all metals were not likely to induce any health hazards to humans, and the target hazard quotient for B, Si, V, Al, Cr, Mn, Fe, Ni, Zn, and Pb showed potential for substantial health risk hazard. The findings of this study generally reveal that the concentrations of the analysed metals exceeded the permissible limits established by the World Health Organisation and the Food and Agricultural Organisation. Given the high levels of metals detected in the soil and vegetables within the study area, it is important to investigate the potential implications for human health and mitigate both acute and chronic health challenges associated with heavy metal exposure. Furthermore, this study will guide policymakers in developing improved regulations and safety standards for agricultural practices and environmental protection, particularly for vulnerable peri-urban and rural communities.