| In this study, we carried out the pot experiments on the multiple contamination soil of Pb, Cd and As. We study the impact of six treatments, CK, Aembic Flood (AF), Limestone (L), Limestone+Aembic Flood (L+AF), Hydroxyapatite (H), and Hydroxyapatite+Aembic Flood (H+AF), for the physical and chemical properties of the soil, the concentrations of heavy metals and As in the soil solution, the concentrations of Pb, Cd and As in the soil, the bound fraction of the Pb and Cd (exchangeable fraction, bound to carbonates fraction, bound to Fe-Mn oxides fraction, bound to organic matter fraction, and residual fraction), the form of the As (exchangeable fraction, Fe bound fraction, A1 bound fraction, Ca bound, and residual fraction), the Pb, Cd and As concentrations of TCLP in the soil, the concentrations of Pb, Cd and As (iron plaque, root, stem, leaf, husk and brown rice). The results of the experiments are as follows.(1) L, L+AF, and H+AF could significantly improve soil pH value. Compared with the control soil, L and L+AF have the most significant effects, the pH value improved by 1.223 and 1.478, respectively. Compared to L and H, there is no further improvement on soil pH value in treatment L+AF and H+AF. The AF, L+AF, and H+AF treatment result in the increase of soil Eh value. Compared with the control soil, the L+AF and H+AF treatments increased the soil Eh values by 129.66～418.41 mV and 135.38～315.16 mV, respectively. The L+AF and H+AF treatments effectively increased the soil Eh when comparing with the AF treatment. However, compared with the control soil, there were no significant effects on CEC, BS, and OM contents by the five treatments.(2) There were significant effects on Pb, Cd and As concentration in soil exchangeable fraction, TCLP extracts, and solution. Compared with the control soil, the L, H, L+AF, and H+AF treatments could significantly reduce the Pb concentration of soil exchangeable fraction, and the concentration reduced by 96.3%, 81.1%,97.5%, and 81.5%. The L and L+AF treatments could significantly reduce the Cd concentration of soil exchangeable fraction, and the concentration reduced by 74.7% and 77.1%, respectively. The L+AF treatment could significantly reduce the As concentration of soil exchangeable fraction, and the concentration reduced by 69.7%. Compared with the control treatment, the concentrations of Pb and Cd in TCLP extracts significantly decreased on the H and H+AF treatments, and the Pb concentrations reduced by 73.7% and 72.5%, and the Cd concentrations reduced by 20.1% and 27.1%, respectively. The concentrations of As in TCLP extracts significantly decreased on the L+AF and H+AF treatments, and the concentrations reduced by 74.2% and 80.7%, respectively. Compared with the control treatment, the Pb concentrations in soil solution decreased 34.2%,34.2%, and 43.9%, respectively, when applying the AF, H, and H+AF treatments. The Cd and As concentrations in soil solution significantly decreased when applying the L+AF and H+AF treatments. Therefore the L+AF and H+AF treatments could decrease the bioavailability of Pb, Cd, and As in soil.(3) There were no significant effects of AF, L, H, L+AF, and H+AF on rice growth and biomass. Compared with the control treatment, the Pb concentrations of the iron plaque in the treatments H, L+AF, and H+AF significantly reduced by 58.3%, 38.5%,64.7%, respectivley; and the Cd concentration of the iron plaque in the L+AF treatment reduced 51.7%; while there were no significant effect on the As concentrations of the iron plaque in all treatments. Compared with the control treatment, the L and L+AF treatments could significantly reduce the concentrations of Pb in rice root, and the Pb concentrations reduced by 13.3% and 40.1%, respectively; the H, L+AF, and H+AF treatments significantly reduce the Cd content in rice root, and the Cd concentrations decreased by 80.8%,79.3%, and 75.5%, respectively; and the H+AF treatment significantly reduce the As content in rice root (47.0%). For the brown rice, the Pb, Cd, and As concentrations of brown rice significantly decreased by the L+AF and H+AF treatments. Compared with the control treatment, the concentrations of brown rice reduced by 53.5% for Pb,45.1% for As, when under the L+AF treatment; the concentrations of brown rice reduced by 40.3% for Cd,47.9% for As, when under the H+AF treatment. In addition, the Cd concentrations of brown rice lower than the tolerance limit of contaminants in foods as set by the China National Standards (GB 2762-2012, Pb and Cd< 0.2 mg/kg) when under the L+AF and H+AF treatments. Consequently, it indicated that the L+AF and H+AF treatments were the effective measures to reduce the Pb, Cd, and As concentrations of rice. |
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