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

This study conducts a quantitative health risk assessment of heavy metal exposure through consumption of vegetables produced on peri-urban irrigated farms in Kano, North West Nigeria, where a long history of wastewater irrigation has raised concerns about cadmium, lead, and arsenic accumulation in food crops. Peri-urban vegetable farming in Kano contributes significantly to the city's fresh vegetable supply, and characterising the health implications of metal contamination in locally produced vegetables is essential for food safety management. Vegetable samples representing the six most commonly consumed leafy and fruiting vegetables were collected from fifteen irrigated farm sites across the Challawa River floodplain. Irrigation water samples were collected from all sites. Metals including cadmium, lead, arsenic, chromium, and zinc were quantified in vegetable tissue and water by inductively coupled plasma optical emission spectrometry. Daily intake calculations used consumption frequency and serving size data from a dietary survey of 200 Kano consumers. Carcinogenic and non-carcinogenic risk estimates were calculated using USEPA risk assessment guidelines for children and adults. Results show cadmium and arsenic in leafy vegetable samples exceeding WHO food safety standards at sites irrigated with heavily contaminated Challawa River water. Non-carcinogenic hazard indices for cadmium exceed unity for children consuming leafy vegetables three or more times weekly. Carcinogenic risk from arsenic consumption is above the acceptable level at multiple sites. Selenium and zinc at normal dietary intake levels do not pose concerns. The study recommends restrictions on wastewater irrigation for leafy vegetable production. Keywords: health risk assessment, heavy metals, peri-urban agriculture, food safety, Kano.