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我国在过去的几十年里,由于金属的大量开采和冶炼[1]、污水灌溉[2]、化肥的不合理施用[3],镉砷在农田土壤中不断地积累。镉砷是毒性较大的重金属,农田土壤中重金属总量超标现象会通过食物链对生态系统和人类的健康构成威胁。根据原环境保护部和国土资源部2014年4月公布的《全国土壤污染状况调查公报》[4],全国镉污染物点位超标率为7.0%,位居重金属污染物榜首;砷污染物点位超标率为2.7%,砷超标的问题也不容忽视。因此,土壤镉、砷超标的环境问题亟待解决。
修复重金属污染农田有多种修复技术,其中使用修复材料将农田土壤的重金属钝化的技术因其具有成本低廉、修复时间短、效果显著的优点[5],具有广泛的应用前景。然而,GONG等[6]认为,这些钝化技术的研究大多停留在条件容易控制的实验室研究阶段,实际应用条件的复杂性可能会影响修复效果及可行性。近年来,针对镉污染土壤现场修复有效的钝化材料包括生物炭材料[7]、磷酸盐材料[8]、黏土矿物[9]等,黏土矿物因其来源丰富、成本低廉、效果显著等特点已被广泛研究[6]。TAHERVAND等[10]发现,黏土矿物具有很强的吸附重金属的能力,但黏土矿物对重金属的吸附存在选择性。目前,研究用黏土矿物进行砷的固定修复的研究比较少,砷污染土壤的修复材料以铁基材料为主[11]。
镉砷是2种性质极不相同的元素,农田重金属污染大多是复合污染,适合镉单一污染修复的材料和适合砷单一污染修复的材料能否用于农田镉、砷复合污染修复尚有待研究。国内外的学者们普遍研究单一修复材料对农田重金属的钝化效果,而不同修复材料之间的修复效果缺乏比较。因此,本研究比较分析了不同修复材料(硅藻土、膨润土、海泡石、人造沸石)和农田调理剂对农田土壤镉、砷的钝化效果,探究了修复材料处理后土壤中的镉、砷的形态以及土壤理化性质的变化,通过种植水稻并检测水稻内的镉、砷含量来检验修复效果,从而为镉砷污染农田土壤现场修复提供参考。
5种钝化剂对镉砷污染稻田的田间修复效果对比
Comparative of the field remediation effect of cadmium and arsenic contaminated paddy by five passivators
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摘要: 为选取费效比高的镉砷复合污染稻田土壤修复材料,比较了黏土矿物和调理剂不同投加组合对稻田土壤中镉砷的田间修复效果,并且针对种植水稻进行了修复效果的验证;研究了修复前后稻田土壤镉砷的有效形态变化、镉砷的形态分布变化、土壤理化性质变化、成熟期水稻产量和水稻各部分镉砷的含量。结果表明,修复100 d后,不同修复材料的二乙烯三胺五乙酸提取态Cd浓度与空白对照组相比均有明显下降;各修复材料均能提高土壤中Cd的残余态(RS)和As的有机结合态(OM)。修复材料处理后,土壤pH均有所提升,其他理化性质初期虽有所变化,但最终会恢复到空白对照组的水平附近;除1 kg·m−2的膨润土处理外,其他材料处理后水稻干谷产量均有所提升;农田调理剂处理后水稻的可食用部分Cd含量最低,修复率达到72.0%。水稻的可食用部分As含量无显著差异,籽粒中Cd和As平均含量符合食用标准。调理剂在田间修复镉砷复合污染稻田土壤中有明显优势,黏土矿物仅适用于镉污染农稻田土壤的修复。Abstract: In order to select high cost-effectiveness remediation materials for Cd-As combined contaminated paddy soil, the field remediation effects of Cd-As in paddy soil by the different combinations of clay minerals and conditioner(F) were compared, and their remediation effects were verified by rice planting. For the paddy soils before and after remediation, the available contents and the species distribution of Cd and As in them, their physical and chemical properties, the yield of rice at maturity and the content of cadmium and arsenic in various parts of rice were studied. The results showed that the extractable Cd concentration of diethylenetriamine pentaacetic acid from 100 d remediated paddy soils with different repair materials decreased significantly, which were compared with the blank control group. The actions of each remediation material could improve the residual state (RS) of Cd and the organic binding state (OM) of As in soil. The soil pH increased after the treatment of the remediation materials, and some changes occurred at first for other physical and chemical properties, while these properties could restored to the level of the blank control group at last. Except for bentonite treatment with 1 kg·m−2, the dry grain yield per mu of rice increased when paddy was treated by other materials. After conditioner (F2) remediation, Cd content in edible part of rice was the lowest, and the recovery rate reached 72.0%. There was no significant difference in As content in edible parts of rice, and the average contents of Cd and As in grains met the food standard. Conditioner has obvious advantages in field remediation of Cd-As contaminated paddy soil, while clay minerals are only suitable for remediation of Cd contaminated paddy soil.
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Key words:
- cadmium contamination /
- arsenic contamination /
- paddy soil /
- clay minerals /
- farm conditioner /
- field remediation
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表 1 实验田各时期Cd和As总量
Table 1. Total cadmium and arsenic content in paddy field during different periods
mg·kg−1 样品 总Cd浓度 总As浓度 秧苗期 分蘖期 成熟期 秧苗期 分蘖期 成熟期 CK 1.22 1.13 1.16 14.10 14.05 14.28 D 1.16 1.13 1.13 13.20 13.62 14.01 F1 1.06 1.08 1.15 17.06 14.06 14.15 AZ1 1.06 1.09 1.07 16.84 13.49 13.83 S1 1.12 1.11 1.01 15.66 13.25 13.37 B1 1.10 1.09 0.99 15.19 13.24 13.32 F2 1.09 1.12 1.02 15.76 13.07 13.94 AZ2 1.07 1.12 1.00 13.96 12.81 12.85 S2 1.05 1.11 0.97 14.02 12.77 11.44 B2 0.99 1.10 0.95 16.76 11.41 11.17 表 2 土壤理化性质的变化
Table 2. Changes of basic physical and chemical properties of soil
阶段 样品 pH 速效磷/(mg·kg−1) 碱解氮/(mg·kg−1) 有机质/(g·kg−1) 阳离子交换量/
(cmol·kg−1)秧苗期 CK 6.02±0.01 33.9±10.2 148±6 32.1±0.8 7.53±0.01 D 5.91±0.07 29.3±2.2 165±0 30.5±0.3 7.74±0.07 F1 6.93±0.04 42.0±4.2 142±25 28.3±5.6 9.16±0.03 AZ1 7.61±0.01 25.1±9.1 137±10 27.6±4.5 7.66±0.30 S1 6.99±0.05 27.4±6.0 204±4 22.8±2.7 8.41±0.64 B1 6.19±0.13 28.7±6.0 164±15 24.0±0.1 8.75±0.01 F2 6.95±0.01 119±27.5 170±5 27.1±4.2 9.38±0.13 AZ2 7.30±0.25 31.1±4.7 292±4 23.7±1.1 8.42±0.55 S2 7.36±0.13 38.3±0.5 320±4 20.0±1.1 9.71±0.02 B2 6.23±0.08 28.4±6.4 330±3 26.1±0.1 8.92±0.13 分蘖期 CK 5.60±0.03 15.9±1.0 88.6±0.2 36.9±0.2 6.10±0.30 D 5.40±0.12 17.3±3.3 81.8±4.8 27.6±5.2 7.70±1.30 F1 5.93±0.04 26.9±1.8 84.7±3.9 30.1±5.3 7.04±1.16 AZ1 6.86±0.02 14.8±0.3 85.5±1.1 38.2±2.3 7.60±0.20 S1 6.49±0.11 14.7±1.8 86.6±9.6 29.3±0.5 9.80±0.20 B1 6.55±0.00 17.2±0.1 77.1±0.1 34.3±0.6 7.14±0.74 F2 6.35±0.01 35.0±4.7 85.6±8.4 22.8±6.9 5.00±0.40 AZ2 6.47±0.03 33.0±2.3 74.0±0.2 14.8±7.4 5.30±0.10 S2 6.38±0.02 22.1±0.1 96.5±7.4 33.9±1.0 5.50±0.30 B2 5.92±0.01 34.1±0.4 73.7±3.0 34.1±8.9 6.64±0.04 成熟期 CK 5.89±0.01 21.3±5.9 95.8±14.9 21.9±3.8 5.88±0.04 D 5.62±0.02 20.7±0.3 106±4.2 33.1±1.8 6.24±0.04 F1 6.18±0.02 45.5±3.4 86.0±3.5 34.4±2.0 7.74±1.30 AZ1 6.64±0.01 21.5±0.9 89.0±0.1 35.7±4.8 6.14±0.30 S1 6.33±0.21 19.5±0.4 95.4±3.3 35.8±0.9 6.27±0.19 B1 6.29±0.02 9.90±0.6 94.4±11.8 30.2±4.5 6.27±0.19 F2 6.27±0.04 41.5±2.7 87.8±1.7 31.3±0.2 5.11±0.19 AZ2 7.07±0.02 26.1±0.7 98.2±8.7 23.4±6.4 5.11±0.19 S2 6.93±0.08 23.6±1.0 101±5.4 22.2±1.5 6.76±0.10 B2 6.59±0.06 29.6±0.8 76.9±0.2 15.0±3.6 8.32±0.49 -
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