Integrated Assessment of Stabilization in As- and Pb-Contaminated Mine Soils Using Fishery By-Product Shells: Implications for Soil Health and Crop Safety

Arsenic (As) and lead (Pb) contamination of soils surrounding abandoned mines threatens environmental safety and limits their potential for agricultural reuse. Although calcium-based materials are widely used for heavy metal stabilization, integrated assessments of shell-based stabilizers considering both contaminant immobilization and soil functionality remain limited. This study assessed the effectiveness of shell-based stabilizers derived from fishery by-products, namely cockle and manila clam shells, which are primarily composed of calcium carbonate (CaCO3), and their influence on soil health and crop safety. The shells were processed into natural and calcined forms and applied to As- and Pb-contaminated soils. Stabilization was evaluated using extraction tests, soil health indicators, and a lettuce cultivation experiment. The natural and calcined shell treatments reduced the extractable concentrations of As and Pb. Calcined shells exhibited higher immobilization efficiency due to Ca–As precipitation and the formation of calcium silicate hydrate and calcium aluminate hydrate phases. However, these treatments induced excessive alkalinity, negatively affecting soil chemical properties and overall soil functionality. In contrast, natural shell treatments provided a more balanced performance by reducing heavy metal mobility while maintaining favorable soil conditions. Lettuce grown under the stabilization–cover soil system showed at least an 87.4% reduction in As concentration compared with the control, while Pb was not detected in any stabilization-cover soil treatment. These results highlight the importance of evaluating shell-based stabilizers within an integrated framework that considers both contaminant immobilization and soil health.