Human health risks of potentially toxic elements in the soil-crop system of a coal mining area, Moatize, Mozambique

This study investigates the pathways by which potentially toxic elements (PTEs) enter the environment during coal mining activities in Moatize, Mozambique. Using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Ion Chromatography (IC), samples of coal (n = 11), soil (n = 18), sediment (n = 4), and food crops (n = 15) were analysed. Results confirm significant accumulation of PTEs in coal. Environmental contamination is evident, as mean concentrations of Al, Co, Fe, and Mn in soil and sediments surpass the standards established by the Food and Agriculture Organization/World Health Organization (FAO/WHO). In crops, Cr (0.92-4.16 mg/kg) and Ni (0.47-1.18 mg/kg) exceeded the permissible limit (0.1 mg/kg) in 60% of samples. Enrichment factors (EF > 2) for As, Co, and Ni indicate an attribution to anthropogenic activity, whereas an extreme ecological risk (Er > 320) for As and Co suggests that mining activities are the predominant sources. The Toxicity Risk Index (TRI) indicates higher ecological stress in soils (65% high TRI) than sediments, primarily due to As and Cr toxicity. Human health assessments confirmed non-carcinogenic risks, with Hazard quotients (HQ > 1.0) for Al, Mn, and Fe in adults and Al and Fe in children. Bioaccumulation factors were higher in Cowpea than Zea mays, posing a greater risk to consumers of local food crops. Although the cumulative hazard index (HI) for Cr, Cu, Ni, and Zn remained low, Cr posed the highest carcinogenic risk, especially for adults. These findings emphasise the importance of regular monitoring and sustainable land-use practices to reduce ecological and human health risks and safeguard the Moatize ecosystem.