Nickel uptake in leafy greens from contaminated soil: an investigation into phytoavailability and health risk assessment using in vitro digestion model.

Nickel (Ni) is a toxic metal that not only pollutes the environment but also causes harmful impacts on plant growth and human health. Therefore, it is crucial to assess the relationship between the phytoavailability of Ni in soil and its accumulation in edible and non-edible parts of vegetables. A pot experiment was conducted to investigate Ni uptake in three different leafy vegetables, spinach (Spinacia oleracea L.), lettuce (Lactuca sativa L.), and fenugreek (Trigonella foenum-graecum L.), grown in soil artificially contaminated with Ni at three different treatment levels (100 mg kg, 200 mg kg, and 300 mg kg). The potential dietary toxicity of these vegetables in humans was examined by using an in vitro digestion model. The lowest and highest chlorophyll contents were detected in lettuce at 300 mg kg of Ni concentration and in control plants of spinach. Their values were 34.16 ± 3.01 (SPAD unit) and 53 ± 3.7673 (SPAD unit), respectively. Among the three vegetables, lettuce and spinach at 300 mg kg exhibited the highest accumulation of Ni, with 43 mg kg in edible parts and 182 mg kg in non-edible parts. Furthermore, health risk index (HRI) values were found to be > 1 for lettuce and fenugreek at Ni concentrations of 200 and 300 mg kg for both children and adults. The average bioaccessibility of Ni in lettuce, fenugreek, and spinach during the gastrointestinal phase was 32-23%, 24-10%, and 45-37%, respectively, at a Ni concentration of 300 mg kg. All three vegetables grown on Ni-contaminated soil may potentially contribute to food chain toxicity. The HRI values being > 1 suggest that these vegetables are unsafe for consumption. Monitoring of Ni concentration in leafy vegetables is essential to minimize human health risks associated with food chain contamination.