Effectiveness and Heterogeneity of Microbially Induced Carbonate Precipitation for Heavy Metal Immobilization: A Meta-Analysis

Microbially induced carbonate precipitation (MICP) has been confirmed to immobilize heavy metals by reducing their lability and leaching. However, the overall effects of MICP on labile/bioavailable and leachable heavy metal concentrations, the extent of between-study variation, and the factors associated with this variation remain unclear. In this study, we conducted a meta-analysis of 21 studies contributing 89 effect sizes to quantify the effects of MICP on labile/bioavailable and leachable heavy metal concentrations and to examine factors associated with these effects. Our results indicate that MICP treatments (including both MICP-only and Additive-assisted MICP) reduced these concentrations by an average of 69.8% (p < 0.001) and 57.5% (p = 0.029), respectively. Treatment effects showed substantial heterogeneity (total I2 = 99.97% and 99.89%, respectively), which was mainly attributable to between-study differences. Additive-assisted MICP showed larger reductions in labile/bioavailable heavy metal concentrations (80.7%) than MICP-only treatments (66.1%) (Holm-adjusted p = 0.012). These findings can inform the selection of MICP-based treatments for heavy metal immobilization in contaminated soils and mine tailings. Future research should optimize treatment conditions, identify sources of heterogeneity, and evaluate the persistence of immobilization effects and environmental benefits through prolonged field experiments.