Remediation of Lead and Cadmium Co-Contaminated Soil by Heavy Metal Resistant Bacteria and Maize Straw Biochar: Performance and Mechanism

Heavy metal pollution affects the stability of soil ecosystem causes food safety problems and human health risks. Thus, effective heavy metal remediation technologies are urgently needed. In this study, the removal ability and mechanism of <i>Leclercia adecarboxylata</i> H25 (H25) and <i>Enterobacter cloacae</i> J1 (J1) against Pb and Cd was investigated, and the remediation effects of Pb, Cd co-contaminated soil with H25/J1 and maize straw biochar was explored. The SEM-EDS and XRD indicated the formation of metal precipitates on bacterial surface after Pb/Cd exposure. FTIR analysis showed that functional groups (C=O, N-H, –PO₄ etc.) on cell surface were involved in heavy metal removal. Application of H25/J1 individually or together with biochar declined the acid-extractable fraction while enriching the residual fraction of Pb, Cd in soil. This was accompanied by the decreased bioavailability of metal elements and increased soil urease, catalase, and sucrase activity. Meanwhile, application of bacteria and biochar enhanced biomass accumulation and depressed the heavy metal accumulation of pakchoi plants. The BC+H25 treatment decreased Pb and Cd accumulation in pakchoi by 51.41% and 25.97%, respectively. BC+J1 treatment depressed the Pb and Cd accumulation by 49.56% and 24.47%, respectively. Overall, the bacterial strains H25 and J1 could be used for <i>in situ</i> remediation of Pb and Cd polluted soil, and synergistic effects could be obtained when apply H25/J1 in combination with maize straw biochar. This study provides a way for treatment of environmental sites contaminated with heavy metals.