Title : Reduction of lead, cadmium, and nickel accumulation in edible herbs grown in contaminated soil using horticultural waste residues
Abstract:
Background: Contamination of agricultural soils with lead (Pb), cadmium (Cd), and nickel (Ni) represents a major environmental and food-safety concern. These potentially toxic metals can be transferred from contaminated soil to edible plants, enter the human food chain, and adversely affect human health. This study evaluated the effectiveness of a mixture of woody walnut and almond shells, used as horticultural waste residues, as an inexpensive, readily available, and environmentally sustainable soil amendment for reducing Pb, Cd, and Ni accumulation in edible herbs grown in contaminated soil.
Methods: Walnut and almond shells were repeatedly washed with deionized water, dried, ground into fine particles, sieved, and thoroughly mixed in predetermined proportions. The prepared mixture was incorporated into soil contaminated with Pb, Cd, and Ni, while contaminated soil without the shell amendment served as the control. Seeds of edible herbs were planted in the prepared soils, and the aerial parts of the plants were collected over three successive harvests. Following standard sample-preparation and acid-digestion procedures, Pb, Cd, and Ni concentrations in the soil and plant tissues were determined using atomic absorption spectrometry. All experiments were conducted in triplicate. The data were analyzed using analysis of variance, followed by Duncan’s multiple range test, with statistical significance established at P ≤ 0.05.
Results: Incorporation of the walnut and almond shell mixture did not significantly reduce the total concentrations of Pb, Cd, or Ni in the contaminated soil. However, the accumulation of all three metals in the aerial parts of the edible herbs was significantly lower than that observed in the control group (P ≤ 0.05). The reduction in metal accumulation increased across successive harvests, with the greatest effect recorded at the final harvest. At this stage, Pb and Cd concentrations in edible herbs grown in the amended soil were more than 70% lower than those measured in the control plants. Nickel accumulation was reduced by 79% compared with the control group. These findings indicate that the mixture of woody walnut and almond shells restricted the bioavailability and soil-to-plant transfer of Pb, Cd, and Ni without substantially changing their total concentrations in the soil.
Conclusion: The mixture of woody walnut and almond shells significantly reduced Pb, Cd, and Ni accumulation in edible herbs cultivated in contaminated soil. The amendment was particularly effective in limiting Ni uptake, resulting in a 79% reduction at the final harvest. Therefore, these horticultural waste residues have the potential to serve as a natural, economical, and environmentally sustainable soil amendment for restricting the transfer of potentially toxic metals to edible crops, supporting the beneficial reuse of agricultural by-products, and improving food safety.
Keywords: Walnut shells; Almond shells; Horticultural waste residues; Edible herbs; Lead; Cadmium; Nickel; Contaminated soil; Food safety.
