Stabilizing Effects on a Cd Polluted Coastal Wetland Soil using Calcium Polysulphide.

In this study, different dosages of calcium polysulphide (CaS) were used as an amendment to investigate effects on the immobilizing of Cd in a wetland soil by pot experiment. In addition to chemical analysis (pH and bioavailable Cd concentration), changes in soil enzyme activities, microbial carbon utilization capacity, metabolic and community diversity were examined to assess dynamic impacts on soil environmental quality and toxicity of Cd resulting from ameliorant dosing. Soil pH increased immediately upon CaS amendment compared to the unamended control (CK), and then declined slowly to a level lower than CK. Diethylenetriamine pentaacetic acid (DTPA) extractable Cd concentration was determined to characterize the bioavailability of Cd in the soil. The CaS dose-dependent effect observed that with increasing CaS dosage, the immobilizing efficiency decreased. Soil urease and catalase activity assays and Biolog EcoPlate assay indicated that early stage addition of CaS significantly inhibited soil microbial activities. However, mid and late stage time periods showed the inhibition effects were alleviated, and the microbial activities could be recovered in 1% and 2% CaS treatments. Moreover, with increasing incubation time, microbial community diversity and richness were significantly recovered in 1% and 2% CaS treatments compared to the CK. No considerable changes were observed in the 5% CaS treatment. Conclusively, the 1% CaS amendment was an efficient and safe dosage for the stabilization of Cd contaminated wetland soil. This study contributes to the development of remediation ameliorants and technologies for heavy metal polluted wetland soils.