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  • In situ field-scale remedia...
    Liang, Xuefeng; Han, Jun; Xu, Yingming; Sun, Yuebing; Wang, Lin; Tan, Xin

    Geoderma, 12/2014, Volume: 235-236
    Journal Article

    At present, the remediation of heavy-metal polluted soil is a considerable problem. In this study, in situ immobilization field experiments were conducted by planting rice (Oryza sativa L.) in Cd contaminated paddy soil to determine the optimal remediation mode that would reduce the accumulation of Cd in brown grain. Sepiolite and palygorskite were utilized as amendments, while ordinary and low Cd-accumulating rice cultivars were selected as model plants. The remediation effects of the amendments on the soil and rice were investigated and the potential immobilization mechanisms were analyzed using X-ray diffraction and X-ray photoelectron spectroscopy. The application of sepiolite and palygorskite was found to increase the pH value of the paddy soil, by varying amounts, and significantly reduce the HCl, TCLP, CaCl2, and NH4OAc-extractable Cd concentrations resulting in a notable decrease in the Cd concentration in brown rice. Both sepiolite and palygorskite were found to reduce exchangeable Cd concentrations and increase the carbonate-bound and residual fractions in paddy soil. Precipitation of Cd as carbonates or hydroxides and surface complexation were the main immobilization mechanisms for sepiolite and palygorskite. The concentration of Cd in brown rice of the low Cd-accumulating cultivar from the control plot was 0.72mg·kg−1. Sepiolite treatment reduced the value to 0.18mg·kg−1 below the maximum levels reported by Codex Stan 193-1995 and the national standard of China. It was concluded that chemical immobilization combined with crop cultivar selection could be a suitable proposal for crop safety regulation and sustainable agriculture. Combination of chemical immobilization and low Cd accumulating rice cultivar. In situ chemical immobilization can significantly decrease the bioavailability and bioaccessibility of cadmium in paddy soil. Meanwhile, selection and breeding of low Cd accumulating cultivars is an environmentally friendly and cost effective method for reducing the risk of contamination from Cd in food. The results of this study suggested that safer food production was more likely to be achievable by combining low Cd accumulating cultivars with in situ immobilizing agent amendment of soils. Display omitted •Sepiolite and palygorskite significantly reduced phytoavailable Cd in paddy soils.•Precipitation and surface complexation were main immobilization mechanisms.•Combination of chemical immobilization and low accumulating cultivar was recommended.