Title : Reduction of heavy metal transfer from contaminated soil to edible herbs using horticultural waste residues
Abstract:
Background: The transfer of heavy metals from contaminated agricultural soils to edible crops poses a substantial challenge to food safety. Reusing horticultural residues as soil amendments may offer an economical approach to limiting metal uptake by plants. This study investigated the effectiveness of a walnut and almond shell mixture in reducing the transfer of lead (Pb), cadmium (Cd), and nickel (Ni) from contaminated soil to the edible aerial tissues of herbs.
Methods: Walnut and almond shells were washed with deionized water, dried, ground, sieved, and blended in predetermined proportions. The mixture was incorporated into soil contaminated with Pb, Cd, and Ni. Contaminated soil without amendment served as the control. Edible herbs were cultivated in both treatments, and their aerial tissues were collected over three successive harvests. Metal concentrations in soil and plant samples were measured by atomic absorption spectrometry following acid digestion. Experiments were performed in triplicate, and data were analyzed using analysis of variance followed by Duncan’s multiple range test at a significance level of P ≤ 0.05.
Results: The shell amendment did not significantly alter total soil concentrations of Pb, Cd, or Ni. Nevertheless, concentrations of all three metals in edible plant tissues were significantly lower in the amended treatment than in the control (P ≤ 0.05). The magnitude of reduction increased across successive harvests and was greatest at the final harvest, when Pb and Cd concentrations were more than 70% lower and Ni concentrations were 79% lower than those in control plants. These results are consistent with restricted soil-to-plant transfer, although the mechanisms governing metal availability were not directly assessed.
Conclusion: Walnut and almond shell residues reduced heavy-metal accumulation in edible herbs without significantly decreasing total soil metal concentrations. Their use as a soil amendment offers a promising strategy for limiting metal entry into edible crops while promoting the beneficial reuse of horticultural waste. Further evaluation under field conditions is needed to establish long-term effectiveness and determine whether treated crops meet applicable food-safety limits.
Keywords: Soil-to-plant transfer; Heavy metals; Edible herbs; Walnut shells; Almond shells; Soil amendment; Horticultural waste; Food safety.
