Arsenic, lead and cadmium in mango-associated soils and fruit from a wastewater-influenced agricultural system in Tanzania: a screening-level dietary risk assessment.

Abstract

Wastewater reuse in agriculture is expanding in water-stressed and rapidly urbanising regions, raising concerns about toxic-element accumulation in soils and edible crops. This study assessed arsenic (As), lead (Pb), and cadmium (Cd) in rhizosphere soils and mango (Mangifera indica L.) fruits from a wastewater-influenced agricultural area surrounding the Moshi Municipality wastewater treatment plant (WWTP), Tanzania, and evaluated non-carcinogenic dietary risks under standardized screening scenarios. Fifteen mature mango trees were sampled as independent units, and composite fruit and paired rhizosphere-soil samples were analysed by atomic absorption spectrophotometry. Soil-to-fruit transfer coefficients (TCs), estimated daily intake (EDI), hazard quotients (HQs), and hazard indices (HIs) were calculated. Mean soil concentrations of As, Pb, and Cd were 21.32, 23.38, and 3.23 mg/kg, respectively, with As and Cd exceeding selected Tanzanian guideline values. Mean fruit concentrations were 0.299, 0.864, and 0.536 mg/kg dry weight, respectively. Fresh-weight Cd averaged 0.0456 mg/kg, exceeding the EU maximum level of 0.020 mg/kg. TCs were <1 and ranked Cd > Pb > As. Screening HIs were 0.469 for adults and 1.407 for children, with As contributing ~90%. These scenario-dependent estimates support enhanced monitoring of wastewater-reuse systems, soils, and edible crops.