Biochemical Combination Benefits Remediation of Soil Lead and Cadmium Pollution: Evidence from Sunflowers, Earthworms, and Soil Microorganisms

Soil heavy metal remediation is a key challenge for environmental scientists, with relevant techniques such as phytoremediation, animal remediation, and chemical remediation. Most studies have employed single treatment methods, yielding limited results. The current challenge is to find ways to enhance the efficiency of soil heavy metal removal through combined approaches. Therefore, this study compares the efficiency of biological remediation (B: 10 earthworms involving 3 transplanted sunflowers), chemical remediation (C: 1% biochar + 0.25% nZVI), and combined biological and chemical remediation (BC: 10 earthworms involving 3 transplanted sunflowers + 1% biochar + 0.25% nZVI) in reducing soil Pb and Cd pollution. The results indicated that under high concentrations, the BC remediation approach facilitated greater accumulation in sunflowers, whereas at lower concentrations, it benefited earthworm accumulation. In the BC remediation approach, sunflowers exhibited higher peroxidase (POD) activity and malondialdehyde (MDA) levels compared to B remediation, enhancing their tolerance to high levels of soil Pb and Cd stress. High-throughput sequencing analysis revealed that the BC remediation resulted in a higher soil microbial diversity index and a more complex soil microbial community structure. This study indicated that BC remediation enhances sunflowers' and earthworms' physiological and metabolic tolerance to soil Pb and Cd stress, as well as their accumulation ability.