Microbial induced carbonate precipitation contributes to the fates of Cd and Se in Cd-contaminated seleniferous soils

Bioremediation based on microbial induced carbonate precipitation (MICP) was conducted in Cd-contaminated seleniferous soils with objective to investigate effects of MICP on the fates of Cd and Se in soils. Results showed that soil indigenous microorganisms could induce MICP process to stabilize Cd and mobilize Se without inputting exogenous urease-producing strain. After remediation, soluble Cd (SOL-Cd) and exchangeable Cd (EXC-Cd) concentrations were decreased respectively by 59.8% and 9.4%, the labile Cd measured by the diffusive gradients in thin-films technique (DGT) was decreased by 14.2%. The MICP stabilized Cd mainly by increasing soil pH and co-precipitating Cd during the formation of calcium carbonate. Compared with chemical extraction method, DGT technique performs better in reflecting Cd bioavailability in soils remediated with MICP since this technique could eliminate the interference of Ca2+. The increase in pH resulted in Se conversion from nonlabile fraction to soluble and exchangeable fractions, thus improving Se bioavailability. And Se in soil solution could adsorb to or co-precipitate with the insoluble calcium carbonate during MICP, which would partly weaken Se bioavailability. Taken together, MICP had positive effects on the migration of Se. In conclusion, MICP could stabilize Cd and improve Se availability simultaneously in Cd-contaminated seleniferous soils.