零价铁与腐殖质复合调理剂对稻田镉砷污染钝化的效果研究

Effects of Stabilizing Remediation of Cd and As in Paddy Rice by Applying Combined Zero-valent Iron and Humus

稻田土壤环境中,重金属镉和类金属砷的行为受pH和Eh的影响强烈,这导致了稻田镉砷复合污染治理难度大。该研究研制了零价铁与腐殖质(质量比为12.5?87.5)的复合土壤调理剂(简称复合调理剂),在水稻早稻和晚稻种植前,分别向试验小区施加零价铁、腐殖质、复合调理剂,研究稻田镉砷的同步钝化效果。结果表明,与对照(不施加零价铁与腐殖质中的任何一种)相比,施加2 250kg·hm-2复合调理剂,水稻各部位砷和镉的质量分数显著降低,早稻稻米中镉质量分数从(0.35±0.04)mg·kg^(-1)下降至(0.19±0.04)mg·kg^(-1),总砷从(0.99±0.11)mg·kg^(-1)下降至(0.38±0.04)mg·kg^(-1);晚稻稻米镉从(0.50±0.05)mg·kg^(-1)下降至(0.25±0.02) mg·kg^(-1),总砷从(1.14±0.15) mg·kg^(-1)下降至(0.48±0.07) mg·kg^(-1);单独施加腐殖质,早稻和晚稻稻米总镉质量分数下降至(0.30±0.11)mg·kg^(-1)和(0.34±0.02)mg·kg^(-1),总砷下降至(0.68±0.05)mg·kg^(-1)和(0.83±0.01)mg·kg^(-1);单独施加零价铁,早稻和晚稻稻米总镉质量分数分别下降至(0.32±0.01) mg·kg^(-1)和(0.49±0.02) mg·kg^(-1),总砷下降至(0.48±0.03)mg·kg^(-1)和(0.64±0.13) mg·kg^(-1)。施加复合调理剂可改善土壤理化性质,水稻产量、土壤pH值、水稻根表铁膜中铁、镉和砷的含量显著升高;而土壤孔隙水中亚铁离子、镉离子和三价砷离子的浓度,土壤中磷酸盐提取态砷和二乙基三胺五乙酸(DTPA)提取态镉的含量则显著下降。其中,施加复合调理剂对土壤磷酸盐提取态镉的降低率(早稻和晚稻分别为37.8%和34.1%)远高于单独施加零价铁和腐殖质的降低率的总和(早稻和晚稻分别为15.1%和12.3%),表明零价铁和腐殖质之间的交互作用对抑制镉进入水稻具有协同作用。零价铁与腐殖质复合调理剂具有同步钝化稻米镉砷的功能,可改良土壤,对环境友好。

The behavior and fates of cadmium(Cd)and arsenic(As)in paddy fields are very different due to the influence of soil pH and Eh,this inconsistency poses challenges on their immobilization and remediation.In this study,a composite of zero valent iron(ZVI)and humus(combined conditioner,the mass ratio of ZVI and humus was 12.5-87.5)was prepared.The efficiency of this composite was investigated in field trails with early and late season rice.The untreated soil,and treatments with only ZVI or humus were also included as control groups to compare the remediation effects with the composite conditioner.The accumulation of both Cd and As in different rice tissues decreased significantly in the composite conditioner treatment compared with the control.In particular,the mass fractions of Cd and As in rice grain in the maturing stage of early season rice were decreased from(0.35±0.04)mg·kg^-1 to(0.19±0.04)mg·kg^-1 and from(0.99±0.11)mg·kg^-1 to(0.38±0.04)mg·kg^-1,respectively.In the maturing stage of late season rice,Cd and As were decreased from(0.50±0.05)mg·kg^-1 to(0.25±0.02)mg·kg^-1 and from(1.14±0.15)mg·kg^-1 to(0.48±0.07)mg·kg^-1,respectively.In treatment with only humus,Cd in rice grain was decreased to(0.30±0.11)mg·kg^-1 and(0.34±0.02)mg·kg^-1,As was decreased to(0.68±0.05)mg·kg^-1 and(0.83±0.01)mg·kg^-1,respectively in the maturing stage of the early and late season rice.In treatment with only ZVI,Cd in rice grain was decreased to(0.32±0.01)mg·kg^-1 and(0.49±0.02)mg·kg^-1,As was decreased to(0.48±0.03)mg·kg^-1 and(0.64±0.13)mg·kg^-1,respectively in the maturing stage of the early and late season rice.Single extraction procedures indicated both the bioavailable Cd(DTPA-Cd)and As(phosphate-As)were decreased significantly by the application of composite conditioner.Additionally,Fe^2+,Cd^2+and As^3+in the pore water were decreased,respectively.The application of ZVI or humus separately had limited effect on the immobilization of Cd(<11.5%and<9.0%for the early and late rice maturing stage,respectively),while the composite conditioner significantly reduced DTPA-Cd(37.8%and 34.1%for the early and late maturing stage,respectively),which indicated a synergetic effect on the immobilization of Cd.Therefore,the application of the composite ZVI and humus conditioner could immobilize Cd and As simultaneously.This composite is environment friendly and can improve soil fertility.