Quantitative Risk Assessment of Heavy Metal Exposure from Consumption of Vegetables Grown in Peri-Urban Farms in Kaduna, North West Nigeria

Peri-urban vegetable farming in Kaduna State relies on irrigation water from streams contaminated by urban effluent discharge and industrial runoff, potentially elevating heavy metal concentrations in fresh produce consumed by urban residents who obtain the majority of their vegetables from these periurban sources. This study conducts a quantitative risk assessment of heavy metal exposure from the consumption of irrigated vegetables grown in peri-urban farms along the Kaduna River corridor, North West Nigeria. Lead, cadmium, arsenic, mercury, and chromium concentrations in soils, irrigation water, and edible portions of four vegetable species (lettuce, spinach, tomato, and carrot) are determined by inductively coupled plasma mass spectrometry following microwave-assisted acid digestion. Daily metal intake via vegetable consumption is estimated for adult and child population sub-groups using Nigerian dietary intake survey data from the National Nutrition Survey. Non-carcinogenic risk is characterised by hazard quotient and hazard index calculations, while carcinogenic risk is estimated using cancer slope factors for arsenic and chromium(VI) from the United States Environmental Protection Agency Integrated Risk Information System. Monte Carlo probabilistic simulation using Crystal Ball software propagates parameter uncertainty in the risk estimates. Transfer factors, bioaconcentration factors, and pollution load index values are calculated to distinguish root versus foliar uptake pathways. Findings fill a critical data gap in quantitative dietary metal risk characterisation for peri-urban food production systems in North West Nigeria and support evidence-based food safety governance. Keywords: quantitative risk assessment, heavy metals, peri-urban vegetables, Kaduna, dietary exposure