A 3-year pot experiment was carried out to investigate the efficiencies of hydroxyapatite (H), thiol-functionalized bentonite (T) and biochar (B) alone or in combination in remedying a Cd-Pb-contaminated soil. The application of passivating agents reduced the Cd and Pb mobility in acidic soil and enhanced soil microbial community function. The largest reductions in the Cd and Pb acid-soluble portions were observed under H (33.49%, 37.37%) and hydroxyapatite + thiol-functionalized bentonite + biochar (HTB, 36.70%, 37.31%), respectively. Biological analysis indicated that the AWCD (average well color development) of the B and HTB amendments was 1.42 and 1.51 times higher, respectively, than of untreated soil at 192 h. Moreover, the Shannon-Wiener, Simpson and Pielou indices were significantly increased in these two treatments relative to the values in the other amendment treatments. Therefore, combination amendments, such as HTB, which can reduce the bioavailability of both Cd and Pb and increase soil microbial activity, are recommended for practical applications.
Keywords: Bioavailability; Heavy metal; Microbial community function; Passivating agents.