Ecological effects of biochar-supported nanoscale zero-valent iron on Eisenia foetida in cadmium-contaminated soil: Oxidative stress, DNA damage, gene expression and transcriptomics analysis

Biochar-supported nanoscale zero-valent iron (nZVI@BC) has been widely used in heavy metal contaminated soil for remediation. However, studies on the soil ecological effects of nZVI@BC were rare. In this study, nZVI@BC was synthesized by the liquid phase reduction and GnZVI@BC was prepared by a green synthesis method which was reduced by green tea extract instead of NaBH4. Earthworms (Eisenia foetida) as indicator organisms were exposed to Cd-contaminated soil. The immobilization effects and enrichment in earthworms of Cd were measured. Besides, oxidative stress, DNA damage, gene expression and transcriptomics of earthworms were deeply explored. The results indicated that the immobilization efficiency of BC, nZVI@BC and GnZVI@BC for Cd was 76.01%, 85.49%, and 80.76%, respectively. The effects of Cd on superoxide dismutase, glutathione S-transferase, peroxidase, and catalase in earthworms reduced, reactive oxygen species and malondialdehyde contents decreased, and DNA damage was relieved. In addition, the gene toxicity of Cd to earthworms was restrained, and the genes expression of sod, cat and gst tended to be stable. With nZVI@BC, the main pathways affected by the differential genes were cellular oxidative phosphorylation and transforming growth factor-β signaling pathways. With GnZVI@BC, there were mainly structure of the cell phagosome, metabolism of taurine, hypotaurine, and alanine processes. This study will provide references for ecological risk assessment of nZVI@BC in practical applications.