Simultaneous remediation of Cd and As co-contaminated soil by microbial-induced carbonate precipitation technologies: evidence from laboratory and field studies

The co-contamination of cadmium (Cd) and arsenic (As) in agricultural soils threatens ecosystem safety and human health via food crop accumulation. However, simultaneous remediation of Cd and As remains challenging due to their opposing chemical behaviors. Microbial-induced carbonate precipitation (MICP) is a promising technology for heavy metal remediation. In this study, we developed a novel bioremediation strategy by employing newly isolated Rummelibacillus sp. (ANY-1) and Rummelibacillus pycnus (ANY-2) for simultaneous immobilization of Cd and As via MICP. This study systematically investigated and compared the efficacy of ANY-1, ANY-2, and the model strain Sporosarcina pasteurii in immobilizing Cd and As in both aqueous solution and soil. Results revealed that ANY-1, ANY-2 could not only efficiently remove Cd(II) from co-contaminated aqueous solution (75.08%-93.13%), but also achieve considerable removal of As(III) (16.74%-37.32%). In soil incubation MICP remediation resulted in 47.26%-64.09% and 8.12%-25.74% decline in available Cd and As contents, respectively. XRD and FTIR analyses confirmed that the immobilization of Cd(II) and As(III) by the three strains occurred not only via co-precipitation with CaCO₃ but also through mineralization, forming (Ca₀.₆₇, Cd₀.₃₃)CO₃ and Ca₅(HAsO₄)₂(AsO₄)₂·5H₂O. Biomineralization induced by ANY-1 and ANY-2 upregulated soil urease gene and without negative impacts on soil bacterial communities. Further field experiment demonstrated that ANY-1 can effectively reduce the accumulation of Cd(63.4%) and As(24.4%) in rice grains, without compromising yield. Our findings highlight the potential of MICP as an eco-friendly and effective strategy for mitigating the combined ecological and health risks posed by Cd and As co-contamination in soil.