The Biosorption of Cadmium, Lead, and Arsenic Using Garlic Byproducts and Their Potential for Metal Immobilization in Soil

Metal contamination poses serious environmental and human health risks, which results in the need for low-cost remediation approaches. The utilization of agricultural byproducts for the removal of metal contaminants is considered cost-effective and environmentally sustainable. Garlic byproducts are rich in sulfur-containing compounds, and various functional groups contribute to metal binding. This study aimed to evaluate the potential of garlic stem and peel for the removal of cadmium (Cd), lead (Pb), and arsenic (As) from aqueous solutions and for their immobilization in contaminated soils. Batch sorption experiments conducted at pH 7 for 24 h showed that garlic stem removed 71.5% of Cd and 70.8% of Pb, while garlic peel achieved 65.4% and 79.4% removal, respectively. The higher Pb removal by garlic peel might be attributed to its higher sulfur content. However, both byproducts were less effective in removing As(III) and showed negligible removal of As(V), as these species predominantly occur in neutral or negatively charged species at neutral pH, resulting in weak interactions with negatively charged surface functional groups. Soil incubation experiments were conducted using 1% and 5% amendments of garlic stem and peel in Pb- and As-contaminated soils. Extractable Pb concentrations significantly increased in soils treated with 1% garlic peel because of the formation of labile complexes of Pb with dissolved organic carbon. However, a column experiment to evaluate the impact on Pb mobility under saturated and unsaturated conditions showed that Pb concentration in soil pore water decreased with garlic stem. Pb concentration was lower under saturated conditions, possibly due to the precipitation of Pb as PbS. Although the short-term application of raw agricultural byproducts increased extractable metal concentrations, long-term incubation reduced Pb levels in pore water. These findings suggest that unmodified garlic stem is a promising, cost-effective amendment for Pb immobilization in soil. Nevertheless, caution is needed in its application to prevent unintended metal mobilization in soil.