Nutritional studies and human health risk assessment of selected leafy vegetables from Ondo Town, Ondo State, Nigeria

Leafy vegetables are known for their nutritional value and benefits to humans; however, there have been reports of associated human health risks from their consumption due to heavy metal contamination. This study assessed the concentrations of selected heavy metals (As, Cd, Cu, Cr, Co, Pb, and Ni), proximate composition, nutrient elements (Na, K, Ca, Mg, Fe, Mn, nad Zn), and human health risks of five commonly consumed leafy vegetables. The vegetables are Struchium sparganophora , Telfairia occidentalis , Talinum triangulae , Celosia argentea , and Ocimum gratissimum, which were collected from a major vegetable market—Iyalaje in Ondo City, Western Nigeria. Atomic absorption Spectrophotometer was used for the quantification after acid digestion of the samples in accordance with standard analytical procedures with 80–120% as spiked recovery. The result of the proximate analysis revealed that the percentage moisture, ash, fat, fibre, protein, and carbohydrate contents were in the range of 12.581 ± 0.009—10.546 ± 0.012, 5.849 ± 0.006—3.842 ± 0.007, 9.477 ± 0.015—5.640 ± 0.020, 12.520 ± 0.010–8.976 ± 0.006, 16.382 ± 0.004–10.644 ± 0.003, and 56.898 ± 0.802–43.250 ± 0.001, respectively. For the heavy metals, arsenic (As) has the highest concentration in Celosia argentea (0.065 ± 0.003 mg/kg), followed by chromium (Cr) (0.356 ± 0.313 mg/kg) and lead (Pb) 0.095 ± 0.002 mg/kg for Telfairia occidentalis . Cadmium (Cd), cobalt (Co), copper (Cu), and nickel (Ni) levels were all below FAO/WHO permissible limits, with Cu ranging from 0.670 ± 0.005 to 1.180 ± 0.003 mg/kg. The concentrations in mg/kg of Na, K, Ca, and Mg are in the range of 46.200 ± 1.100–24.633 ± 0.153, 242.667 ± 0.252–79.533 ± 0.305, 112.167 ± 0.153–2.953 ± 0.008, and 18.164 ± 0.004–11.485 ± 0.00, respectively. The estimated daily intake (EDI) values for all metals were below the World Health Organization's tolerable daily intake thresholds for both adults and children. Hazard quotient for children was within the WHO/FAO limit for some elements but above the limit for arsenic in Talinum triangulae, Celosia argentea L., and Ocimum gratissimum (> 1.0). Overall, these vegetables are nutritionally beneficial but could contribute to cumulative heavy metal exposure if consumed in large quantities or sourced from contaminated environments. Findings emphasize the importance of dietary diversity, environmental monitoring, and safe agricultural practices to ensure long-term food safety.