Effective co-immobilization of arsenic and cadmium in contaminated soil by sepiolite-modified nano-zero-valent iron and its impact on the soil bacterial community.

Sepiolite-modified nano-zero-valent iron (S-nZVI) is used as an amendment and incubated to remediate As-Cd-contaminated soil under three different soil‒water management conditions [moderately wet (MW), continuously flooded (CF) and alternately wet and dry (AWD)]. The results showed that soil pH is in the order of CF > AWD > MW. The soil pH increased approximately 0.5 to 1 unit by 3% and 5% doses after 36 d of incubation. Soil pH was negatively correlated with available As-Cd content under the three water regimes (p < 0.01). All doses of S-nZVI significantly reduced soil available As-Cd under the three soil moistures by 45-80% for As and 5-45% for Cd. Moreover, S-nZVI addition also promoted the transformation of As-Cd in the acid-extracted fraction, oxidation fraction, and reduced fraction to a more stable residue fraction. High-throughput sequencing results showed that high doses of S-nZVI had a significant adverse effect on soil bacterial diversity and richness. After 36 d of incubation, the Chao1 index and the Shannon index were significantly decreased in MW, CF, and AWD, respectively. Decreasing the S-nZVI dose and increasing the incubation time simultaneously reduced As-Cd availability and S-nZVI ecotoxicity in the soil, thereby effectively maintaining the survivability of the original dominant bacteria, increasing the soil pH, and promoting the interaction between dominant bacteria and soil factors in As-Cd cocontaminated soil.