Stochastic human exposure-risk modelling and environmental health implications of potentially toxic elements in the Mubuku irrigation scheme, Uganda

Potentially toxic elements (PTEs) contamination of agro-ecosystems poses significant threats to food safety and public health. Study investigated the occurrence, sources, and human health risks of PTEs (As, Pb, Cd, Co, Cr, Hg, Ni, Cu, Fe, Mn, Se, Zn, Th, and V) in irrigation water (n = 1), agricultural soils (n = 9 composite samples), and vegetables (onion, cabbage, and amaranth; n = 36 composite samples) collected in August 2024 from the Mubuku Irrigation Scheme, western Uganda. Elemental concentrations were determined using inductively coupled plasma-optical emission spectroscopy. Health risks were assessed using hazard quotient, hazard index (HI) and total cancer risk (TCR) models, complemented by Monte Carlo simulation (MCS; 10,000 iterations) to address exposure variability and uncertainty. More than 20% of detected PTEs in vegetables exceeded WHO/FAO limits. Arsenic (2.22-3.57 mg/kg), lead (2.02-3.66 mg/kg), and mercury (0.42-0.61 mg/kg) consistently exceeded guideline values (0.1, 0.3, and 0.001 mg/kg, respectively), with amaranth as the highest accumulator. Irrigation water contained elevated As (1.56 mg/L) and Pb (2.73 mg/L). Estimated HI values indicated considerable non-carcinogenic risks (HI > 1). TCR and MCS exceeded acceptable thresholds (10⁻⁶-10⁻⁴), highlighting probable lifetime cancer risks and the need for targeted risk management interventions.