Facile combinations of thiosulfate and zerovalent iron synergically immobilize cadmium in soils through mild extraction and facilitated immobilization

Cadmium (Cd) is one of the most toxic substances released in the environment. Cd-contaminated soils usually have a large pool of bioavailable Cd species and lead to excessive Cd accumulation in planted cereal crops. Treatment methods for stable immobilization of Cd in soils are desirable. Here we reported that facile combinations of thiosulfate (STS) and zerovalent iron (ZVI) reinforced Cd immobilization in soils and reduced Cd accumulation in wheat. STS mildly activated Cd in soils through the formation of soluble Cd(S2O3)(x) complexes, whereas intermediates of STS (e.g., sulfate and sulfides) and ZVI synergically facilitated immobilization of Cd in soils. The synergy was ascribed to the facilitated formation of FeOOH with high Cd-binding affinity and formation of stable sulfate-Cd-FeOOH complexes and poorly available CdSx. STS-ZVI treatments increased residual Cd in soils by 101-123% and decreased Cd accumulation in wheat shoots by 13-68%, depending on chemical compositions and doses of binary reagents. Field applications of STS and ZVI (0.06-0.11 kg/m(2)) demonstrated 24-39% reductions of grain Cd.

Automated summary

The combination of thiosulfate (STS) and zerovalent iron (ZVI) was found to enhance the immobilization of cadmium (Cd) in soil and reduce Cd accumulation in wheat, potentially providing a sustainable solution to Cd-contaminated soils. The synergistic effect of STS and ZVI improved the formation of stable Cd-binding complexes in soil, resulting in decreased Cd uptake by wheat plants. Field applications of STS and ZVI demonstrated significant reductions in grain Cd content, highlighting the potential of this treatment method for remediation of Cd-contaminated environments.