【作者】 陈亚华；

【导师】 沈振国；

【作者基本信息】 南京农业大学 ， 植物学， 2006， 博士

【摘要】 土壤重金属污染是一个世界范围内普遍关注的环境问题。采用螯合剂强化植物提取污染土壤重金属是近十年来重金属污染土壤修复的研究热点之一。本文通过开展农田重金属污染情况调查，研究螯合剂种类、处理浓度以及与高生物量植物的匹配关系，探索提高螯合剂诱导植物富集土壤重金属效率的方法，研究采取防止螯合诱导修复过程重金属淋滤的措施，并进行了多年的盆钵及野外田间植物提取试验等工作，较为系统地研究了诱导性植物提取修复重金属污染土壤的原理和方法。1、通过对南京市5县4郊5个环境单元（矿冶区、交通干线、工厂周边、污灌地、农产品基地）共100个样点的农田土壤及蔬菜样品重金属（Pb、Cu、Zn、Cd）污染情况调查，发现不同功能区土壤重金属含量存在明显差异：矿区周边农田污染最为严重，其次为污灌地和公路沿线农田，部分农产品基地存在轻度Cd污染，工厂周边农田土壤污染相对较小。蔬菜重金属含量与土壤重金属生物有效性含量和总量之间存在极显著相关。重金属污染严重的矿区农田土壤，蔬菜食用部分重金属含量普遍超过国家食品卫生标准。不合理的矿业开采和冶炼是导致南京地区农田土壤和蔬菜重金属污染的主要原因。2、通过土培试验，比较分析了螯合剂（EDTA、EDDS）诱导10余个植物品种提取污染土壤重金属的潜力。结果表明，螯合剂处理可以有效促进重金属从植物根系向地上部分的转运，提高植物地上部分富集重金属的能力。研究发现：和单子叶植物（如大麦、小麦、高粱、玉米、香根草等）相比，双子叶植物（如绿豆、荞麦、豌豆、油葵、芥菜等）对螯合剂处理更为敏感，表现为植株毒害症状较早出现，地上部分重金属浓度增加幅度更大。综合考虑植物地上部分重金属浓度、植物生物量、植物生长的季节性因素等，芥菜、豌豆可以作为冷季型植物的首选，而玉米、油葵、绿豆、荞麦等可以作为暖季型植物的首选。香根草由于其独特的生物学特性：深根系、生长迅速、生物量大、蒸发量高、极高的耐逆性能等，在植物稳定方面可以发挥重要作用。3、通过多年的盆栽试验，研究了在对第一季植物（油菜）一次性施加四种水平EDTA(0，1.25，7.5，17.5 mmol·kg^-1)处理后，后续六季植物（玉米、油菜）连续修复Pb污染土壤的潜力。研究结果表明，EDTA在土壤中存在残留效应，可以促进后季植物对土壤Pb的提取，但施用浓度过高，对后季植物有生理毒性，并抑制其生长和减少植物对土壤Pb的提取。低浓度EDTA处理对土壤Pb的降低没有效果，随EDTA处理浓度的加大，土壤Pb含量降低幅度也越大。但是，七季植物地上部分提取总Pb量不足土壤总Pb量下降值的1％。因此，土壤中可溶性Pb的淋滤是导致土壤总Pb量下降的主要原因。4、通过盆栽试验，研究了多种调控措施对提高植物提取土壤重金属效率的方法。研究发现，土壤添加物（如N肥、K肥、不同有机肥、生根粉等）以及一些叶面处理（如微肥、Si肥、植物生长调节剂）等措施对诱导玉米幼苗富集土壤重金属的作用均显著不如EDTA的诱导作用。研究发现，一种野生杂草—泽漆，其茎分泌的汁液对土壤难溶性Cu具有比较高的溶解能力，土壤添加泽漆干粉对诱导玉米富集土壤Cu有明显的促进作用。野生泽漆汁液有望成为一种天然的螯合剂。5、采用土柱淋滤试验，研究了螯合剂（EDTA、EDDS）诱导植物（油葵、玉米、香根草等）修复过程中的重金属淋滤行为，同时研究了降水因素对重金属淋滤行为的影响以及深根系植物香根草在减少重金属淋滤方面的作用。结果表明，在大量雨水的淋洗下，EDTA辅助的植物修复容易导致上层污染土壤重金属向地下水的淋滤。而易生物降解性螯合剂（EDDS）由于在土壤中的半衰期大约只有10-20天，因此对土壤重金属的迁移行为影响不大。在25天时间内经过480mm降水量的淋洗，在80 cm高的土层下方没有收集到重金属淋滤液，说明EDDS具有比较高的安全性。土柱种植香根草和玉米可以有效延缓螯合剂诱导修复中的重金属淋滤，且香根草的效果要好于玉米。植物延缓重金属向下层土壤迁移的原因主要来自于植物通过蒸腾作用导致土壤含水量的降低，而非通过植物地上部分的截取。研究发现，植物地上部分积累的重金属量大约占土壤可溶性重金属总量的0.1％，说明螯合剂诱导植物提取土壤重金属的效率很低。研究发现，在8周的时间内，（模拟淋滤的）螯合态Pb可以全部被土壤介质吸附。与Pb相比，螯合态Cu被土壤吸附的比例较少。如果提高土壤有机质水平可以在2周内全部吸附螯合态Pb或Cu，因而减少了污染再次迁移的风险。6、通过盆栽试验，研究了提高土壤温度对螯合剂（EDTA和EDDS）诱导植物（玉米和绿豆）提取土壤重金属的效应。研究结果表明：通过水浴处理、热溶液浇灌处理、地下铺埋热水管等多种方法提高土壤温度可以有效提高螯合剂诱导植物提取土壤重金属的效率。研究发现，在螯合剂施用2天后进行热处理有最高的提取效率。采用在地下铺埋PVC管，并在PVC管内通入循环流动的热水（50℃）以提高土温，该方法可以提高螯合剂的使用效率约5倍（绿豆）和10-14倍（玉米）。此值是目前文献报道中提高螯合剂使用效率的最高值。通过提高土温可以提高螯合剂使用效率，减少螯合剂的施用量，从而达到降低螯合剂使用成本以及减少可溶性重金属向地下水迁移的潜在危险。该方法为修复重金属污染土壤提供了一种新的工艺技术。7、通过水培试验，研究了螯合剂诱导植物吸收重金属的机理。结果表明，根系的机械损伤（剪根和拍根）对玉米地上部分富集Pb的作用影响不大。然而，根系进行预热处理可以显著增加Pb从根系向地上部分的转运，尤其是Pb以Pb-EDTA螯合形态存在时增加量尤为显著。通过根系活力与植物地上部分重金属含量的相关性可以看出，植物对Pb的吸收是一个非主动吸收的过程。通过提高环境湿度，减少植物的蒸腾作用，可以显著降低地上部分重金属的积累，说明重金属向地上部分的运输是一个被动运输的过程。结合土培试验结果，高浓度螯合剂或重金属离子对植物根系的伤害可以导致螯合态重金属通过质外体途径大量进入根系木质部，在蒸腾拉力的作用下，重金属被动运输并富集在植物地上部分。8、对江苏南京伏牛山铜矿区一个铜污染农田进行了为期3年的野外田间植物提取试验。在污染农田种植了7季作物（玉米和油菜连作），对部分土壤施加了EDTA处理(总EDTA施用量为2.18 mmol kg^-1土)。结果表明：未施加螯合剂处理的土壤0-20cm土层铁锰氧化物结合态、有机物结合态和残渣态铜含量在近3年的时间内没有变化，而可交换态和碳酸盐态结合态铜含量分别下降到三年前的57％和84％，土壤总铜含量下降81-98 mg kg^-1。EDTA辅助修复下，0-20 cm土层残渣态铜含量也没有变化，而可交换态、碳酸盐结合态、铁锰氧化物结合态和有机物结合态铜含量分别降低到三年前的48％、39％、67％和81％，土壤总铜含量下降233-312 mg kg^-1。施加EDTA处理，7季植物地上部分总积累的铜量是未施加EDTA处理组的1.6倍。但是，7季植物地上部分积累铜量只占土壤铜含量下降值的0.1-0.2％。20-60 cm土层土壤铜含量也有所下降。土壤中减少的铜99％以上淋滤到地下水。尽管不施加EDTA处理，污染土壤的铜也存在向地下水的自然淋滤。总之，本文通过野外调查、实验室土培及水培试验以及多年的盆钵和野外田间试验等，为诱导性植物提取技术的理论研究及可行性应用提供了大量翔实的试验证据。更多还原

【Abstract】 Heavy metal contamination in soils is one of the most serious environmental problemswith great significance to human health. Chelant-enhanced phytoextration of heavy metalshas evoked most attention in the remediation of heavy metal-contaminated soils. This paperstudied the theory and the methods of chelant-enhanced phytoextraction extensively by theinvestigation of heavy metal contamination in farm lands, the selection of chelators andplant species, the optimization methods of chelators’ application for increasing theefficiency of phytoextraction, the adoption some measures for decreasing the leaching ofheavy metals in the process of phytoextraction, and undergoing several years’ pot and fieldexperiments of phytoextraction heavy metals from contaminated soils.1. Heavy metal contamination in soils and vegetables in five environmental units-mining and smelting area, arterial traffic, factory, sewage irrigation plot and farm producebase-in 5 counties and 4 suburbs of Nanjing city were investigated. The results shown that,the contamination of heavy metals in the above five environmental units diversifiedsignificantly. Soils sampled from mining and smelting areas were the most heavilycontaminated by heavy metals, followed by the soils in sewage irrigation plots and highway.Soils from farm produce bases occurred slight pollution by Cd. Among 5 environmentalunits, soils in peripheral farmlands of factories had the least contamination by heavy metals.The heavy metal concentrations in the shoots of vegetables had a significantly positivecorrelation with the total and bio-available concentrations of heavy metals in soils. Theplant samples from mining and smelting areas had the highest concentrations of heavymetals, which were commonly exceeded the tolerance limitation of heavy metals in foods.Un-normative mining and smelting activity was the major cause of heavy metalcontamination in soils and vegetables in Nanjing area.2. Using pot experiment, the potential use of the eleven plant species, including sixdicotyledon species and five monocotyledon species, was investigated for the EDTA-orEDDS-enhanced phytoextraction of heavy metals from contaminated soils. The resultsshowed that, compared the monocotyledon species （barley, wheat, sorghum, corn, vetivergrass, et al.）, the dicotyledon species （Mung bean, buckwheat, pea, oil sunflower, mustard, et al.） had a higher sensitivity to the EDTA or EDDS treatments, which could be reflectedby the severer toxicity of seedlings and the higher concentrations of heavy metals in theshoots. Considering the three factors （the shoot level of metals, the biomass of plants, andthe growing seasons of plants）, mustard and pea were more suitable used in the coolseasons, and corn, sunflower, mung bean and buckwheat could be selected in the warmseasons. Vetiver grass, owing its’ massive root system, fast-growing, high biomass, highevaporation and high tolerance to stress environments, may be suitable used in thephytostabilization of heavy metals in soils.3. Pot experiments were conducted to investigate the effects of residual EDTA in了soilson the shoot uptake of lead from Pb-contaminated soils (soils amended 0, 500, 2500, 5000mg Pb kg^-1 soil) by the successive 6 crops （corn and mustard）. EDTA at 4 dosages (0, 1.25,7.5, 17.5 mmol EDTA kg^-1 soil) was applied to the Pb-contaminated soils at the first cropmustard. Results showed that, the residual EDTA in soils increased the concentration of Pbin the shoots of the following crops. However, at the high dosage of EDTA treatment (7.5,17.5 mmol·kg^-1), the residual EDTA in soils was toxic to the subsequent crops. With theincrease of planting seasons, the soluble Pb in soils decreased, and the toxicity of cropsdisappeared gradually. At the low dosage of EDTA treatment (1.25 mmol·kg^-1), the Pbconcentration in soils did not changed after the 7 crops planting. Even the Pb concentrationin heavily Pb-contaminated soils decreased significantly after the high dosage of EDTAapplication, the total uptake of Pb by 7 crops accounted less than 1％of the decrease of soilPb, which implied that the decrease of soil Pb mainly caused by the leaching of soluble Pbfrom soils.4. Pot experiments were used to investigate the effects of agronomic regulationmethods on the increasing efficiency of phytoextraction heavy metals from soils. Soilamendments （such as N, K and organic fertilizers） and leaf treatments （such as daubingmicro-nutrient, Si fertilizers and plant growth regulators in the leaves） had less effective atincreasing shoot removal of metals compared to the EDTA treatment. Interestingly, anatural chelator substance--the sap from shoots of Euphoria helioscopia could effectivelysoluble Cu from soils, and the dry powder of Euphoria helioscopia amended to the soilscould enhance the shoot removal Cu by corn seedlings from contaminated soils.5. Using soil column leaching test, the leaching behavior of heavy metals from soilcolumns was investigated in the process of EDTA or EDDS-assisted phytoextraction. The effects of artificial rainfall percolation applied to the soil surface and the plants （oilsunflower, corn and vetiver grass） grown in the soil columns on the leaching patterns ofheavy metals were also studied. Results showed that, the soluble of heavy metals in thecontaminated soils after EDTA application could be persistent in the soils for a long time （atleast 32 weeks）, which could be easily leached down to the deep soils, then leached out soilcolumns after the large rainfall percolation. On the contrary, EDDS application had a littleeffect on the movement of heavy metals in the soils. 2.5 mmol EDDS kg^-1 soil applicationdid not lead to the leaching of heavy metals from the soil columns （80 cm in height） after480 mm precipitation of rainfall percolation within 25 days. This implies that residualEDDS in the soil will rapidly be degraded （the half-life of EDDS in soils was about 10-20 d）and EDDS can be regarded as a good chelator candidate for the environmentally safephytoextraction heavy metals from soils. Corn and vetiver grass seedlings grown in the soilcolumns could be effectively delay the movement of heavy metals from upper soils to deepsoils, and vetiver grass showed more effective than corn. However, the amount of heavymetals absorbed by plants accounted for about 0.1％of the total soluble metals in the soils.In another test, EDTA-Pb or EDTA-Cu solution could be reabsorbed by soil matrix,especially in the soils with high level of organic matters.6. Pot experiments were carried out to investigate the effects of increasing soiltemperature on the shoot uptake of heavy metals by two crops （corn and mung bean） whichgrew in an artificially multimetal-contaminated soil and a naturally Cu-contaminated soil,respectively. After the application of chelator （EDDS or EDTA）, soils were treated withhigh temperature （50℃or 80℃） for 3 h, which significantly increased the concentrationsof heavy metal in shoots. The post-heating treatment 2 days after chelator addition wasmore efficient at enhancing heavy metal concentrations than the pre-heating treatment 2days before the application of EDTA or at the same time with chelator application.Increasing soil temperature by using underground PVC tubes circulated with hot water 2days after the chelator application could increase the efficiency of shoot Cu uptake about10- to 14-fold for corn, and 5-fold for mung bean from Cu-contaminated soils incomparison with the normal chelator application. This was the highest efficiency ofoptimization chelators application reported in the literature up to now. The irrigation of 100℃hot water 2 days after the chelator addition, or irrigation of 100℃chelator solutiondirectly, also resulted in significantly higher phytoextraction of heavy metals in two crops than that treated with 25℃chelator only. These results suggested that increasing soiltemperature could increase the phytoextraction efficiency, and thus minimize the amount ofchelator applied in the field, which would decrease the operation cost and the potential riskof soluble heavy metal movement into ground water. This new technique represents a verypromising engineering-oriented approach to the decontamination of metal polluted soils.7. Solution culture experiments were carried out to investigate the mechanism ofuptake of heavy metals in plants induced by chelators. In hydroponics, roots of corn werepretreated with cutting, flapping or heating stress, and then exposed to the 250μmol L^-1 Pbsolutions with or without 250μmol L^-1 EDTA addition. The results showed that themechanical damage of roots by cutting or flapping had no effect on increasing shoot Pblevel, however, the pre-heating treatment significantly facilitated the Pb transportation fromroots to shoots. Compared to the Pb treated alone, addition of EDTA to the Pb solutionsalleviated the phytotoxicity of seedlings and decreased Pb concentrations in roots, but itincreased Pb levels in shoots. According to the relationships between the root cell viabilityand the shoot level of heavy metals, the uptake of heavy metals by plants was a passiveprocess, which was confirmed by the change of humidity in environment. With the decreaseof evaporation, the shoot uptake of heavy metals decreased accordingly. Considering theresults of pot experiments, the destruction of the physiological barrier（s） in roots caused bythe high dosage of uncoordinated EDTA, or free-Pb²⁺, or other stresses （such as heatingtreatment） could led to the heavy metals diffused into the root xylem via apoplastic pathway.The metals （mostly in the forms of combined with chelator） in the xylem could be quicklytransported upwards by a driving force, i.e., transpirational pull.8. A field experiment, lasting 3 years, was conducted at a farm land located at the eastof Nanjing city, China. Seven consecutive crops （corn and rape） were planted in thenaturally Cu-contaminated soils in order to assess the efficiency of phytoextraction Cu fromsoils with or without EDTA application (total applied EDTA in three years was 2.18 mmolkg^-1 soil). Results showed that, in the control soils at 0-20 cm layer without EDTA treated,the content of Cu in Fe-Mn oxide, organic and residual fractions in soils did not change;however, Cu content in the exchangeable and carbonate fractions decreased 43％and 16％,respectively; and total Cu in soils decreased 81-98 mg kg^-1 after seven crops planting.With EDTA treated, the level of residual Cu in soils at 0-20 cm layer did not change; but theexchangeable, carbonate, organic and Fe-Mn oxide fractions of Cu decreased 52％, 61％, 33％and 19％, respectively; and the level of total Cu in soils decreased 233-312 mg kg^-1jafter seven crops planting. Total uptake Cu in the shoots of seven crops with EDTA assistedwas 1.6-fold that of the controls. However, the amount of total removal of Cu by shoots of7 crops accounted about 0.1-0.2％of the amount of decreased Cu in soils. That is to say,over 99％of the decreased Cu in soils leached into groundwater. Even without EDTAapplication, Cu in contaminated soils would leach into groundwater naturally. The estimatetime to clean-up may actually be somewhat less than 10 years if Cu migrates down in thesoil profile with EDTA addition. The EDTA-assisted removal of Cu from Cu-contaminatedsoils may be feasible if combined with the special equipment for collecting the leached Cusolutions.In summary, the results of this paper will benefit to the further study of the theory andthe practice of chelant-enhanced phytoextraction in heavy metal-contaminated soils.更多还原