| In this study, the transportation and transformation of arsenic (As) in the rhizosphere and non-rhizosphere soils at different rice growth stages were studied. The stabilization effects of Pb, Cd, and As in contaminated soils was investigated by using modified kaolin (burning, burning plus HC1, burning plus NaOH, burning plus A^SCu)}), calcium carbonate, and calcium magnesium phosphate fertilizer. After screening and matching from above materials, a combined amendment with a ratio 4: 2:1 of calcium carbonate:modified kaolin:calcium magnesium phosphate fertilizer was prepared, marked as LMF, which was highly effective on stabilization of Pb, Cd, and As in contaminated soils. Pot experiments of rice planting were conducted to study the stabilization effects of Pb, Cd, and As in contaminated paddy soil system with LMF applying of 0,0.5,1,2,4,8,16 g·kg-1 and to study the adsorption and accumulation of these elements in various rice organs. The main results of this study were given as follows:(1) With the extension of rice growth period, pH values and contents of TCLP extractable As in the rhizosphere and non-rhizosphere soils were increased gradually, and the pH values and TCLP extractable As in non-rhizosphere soils were higher than those in the rhizosphere soils at the same growth stage. At the different growth stages of rice, the contents of exchangeable As (Ex-As) in rhizosphere and non-rhizosphere soils were lower than those before rice planting, and increased gradually with the extension of the rice growing period. The contents of Al-bound As (Al-As), Fe-bound As (Fe-As) and Ca-bound As (Ca-As) increased gradually after rice planting, but not significantly. Residual As (O-As) and total As (T-As) decreased gradually after rice planting, by 37.30% and 14.69% in the rhizosphere soils and by 31.38% and 8.67% in the non-rhizosphere soils, respectively. At the different growth stages of rice, the contents of various As fractions in soils were as follows:O-As> Fe-As> Al-As> Ca-As> Ex-As. In the total soil As, O-As accounted for 46.5%-68.3% and Ex-As for less 0.5%.(2) In the screening test of modified kaolin materials, application 4 g·kg-1 of burning kaolin resulted in a reduction in the contents of soil exchangeable As, Pb and Cd (Ex-As, Ex-Pb, Ex-Cd) by 32.14%,13.03% and 2.78%, respectively, and a reduction in the contents of soil TCLP extractable As, Pb and Cd (TCLP-As, TCLP-Pb, TCLP-Cd) by 29.91%,10.09% and 1.27%, respectively. Application 4 g·kg-1 of LMF resulted in a significant stabilization effect for soil heavy metals and As: compared with the control, soil pH increased by 1.75; contents of soil Ex-As, Ex-Pb, Ex-Cd decreased by 92.86%,93.33%, and 19.10%; and contents of soil TCLP-As and TCLP-Pb decreased by 43.60%,23.17%, but no significant effect was observed for TCLP-Cd.(3) In the pot experiments of rice planting, with increase in the amounts of LMF applying, pH values, total amount of exchangeable base contents (TEB) and cation exchange capacity contents (CEC) increased generally, and there were no significant changes in the contents of base saturation (BS) and organic matter (OM) in soils. Application of LMF changed greatly in the fractions of soil Pb and Cd, which decreased significantly in the contents of exchangeable and acid extractable of Pb and Cd, and organic bound Pb, increased slightly in the contents of Fe-Mn bound Pb and residual Pb, and did not change obviously in the contents of Fe-Mn bound, residual, and total Cd. With increase in the amounts of LMF applying, the contents of TCLP extractable Pb decreased gradually, and there was no significant effect for TCLP extractable Cd. Application of LMF resulted in fraction changes of As in the soils before rice planting (SH) and after rice harvesting (CS). The contents of exchangeable and TCLP extractable As showed a trend of decreasing first and increasing after with increase in the amounts of LMF applying, and the lowest contents of Ex-As and TCLP-As were observed at 2 mg·kg-1 of LMF applying.(4) Application of LMF changed significantly the contents of Pb, Cd, and As in various organs of rice in the pot experiments of rice planting. With increase in the amounts of LMF applying, compared with the control, the contents of Pb and Cd in brown rice decreased by 8.44%-99.57% and 27.49%-74.05%, respectively. At 16 mg·kg-1 of LMF applying, the contents of Pb and Cd in brown rice were 0.002 mg·kg-1 and 0.185 mg·kg-1, respectively, lower than 0.20 mg·kg-1, which was the limited level of pollutant contents in brown rice (GB 2762-2012). The contents of Pb, Cd, and As in brown rice were significantly or high significantly relative between the contents of high activity fractions (acid extractable, extractable, and TCLP extractable) fractions of these elements in soil. |
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