Study on remediation capacity of typical forage grasses for Cu, Pb, and Cd contamination in coal gangue-accumulated soils

Based on the ecological restoration needs of coal gangue accumulation areas, this study focuses on the potential application of in situ remediation techniques using forage plants. Taking the heavy metal pollution characteristics of the shallow soil (0-20 cm) in a typical coal gangue accumulation area in the Fengfeng mining district of Hebei as a prototype, pot experiments were conducted to investigate the heavy metal content in soil and plants under different heavy metal concentration gradients of Cu (14, 64, 100 mg/kg), Cd (1, 4, 8 mg/kg), and Pb (15, 38, 170 mg/kg) for both single and composite pollution types, revealing the heavy metal accumulation coefficients and translocation capabilities of alfalfa Medicago sativa L.(alfalfa) and Lolium perenne L.(ryegrass). The results indicated that:(1) When the soil was polluted by a single heavy metal, compared with ryegrass, alfalfa had better enrichment ability for Pb, and ryegrass had better enrich ability for Cu. When the concentration of Cd in soil was less than 1 mg/kg, the ability of alfalfa to enrich and transport Cd was better than that of ryegrass. (2) When heavy metal Cu-Pb-Cd combined pollution occurred in soil, the ability of alfalfa to enrich Cu and Pb was significantly better than that of ryegrass. The Cu BCF and Pb BCF of alfalfa were 1.14-2.29 and 1.53-3.96 times that of ryegrass, respectively. The ability of alfalfa to enrich high concentrations of Cd was also significantly better than that of ryegrass. The Cd BCF of alfalfa was greater than 1. (3) If the soil contaminated by heavy metal Cu-Pb-Cd is remedied in situ by planting forage plants, the technical strategy of ' selecting alfalfa + selecting or cultivating varieties with developed roots and stems + applying plant roots and stems targeted protective agent ' is adopted.