EDTA對促進受重金屬鎘鋅及鉛污染土壤植生復育之研究

Phytoremediation of Soils Contaminated with Cadmium, Zinc, and Lead Enhanced by EDTA

賴鴻裕(Hung-Yu Lai)

指導教授 ： 陳尊賢

國立臺灣大學/生物資源暨農學院/農業化學研究所/博士(2004年)

https://doi.org/10.6342/NTU.2004.00178

摘要

植生復育技術(phytoremediation)可用於復育重金屬污染土壤，利用植物的根部累積污染土壤中的重金屬，再將重金屬轉移至植物的地上部中，並利用收割以移除土壤中的重金屬，對於部份生物有效性較低的重金屬，則可於土壤中施用螯合劑，增加植生復育的成效。本研究於受鎘、鋅及鉛污染的坋質黏土土壤中種植五彩石竹(Dianthus Chinensis)、培地茅(Vetiver zizanioides)及印度芥菜(Brassica juncea)，利用此三種植物植生復育受多種重金屬污染的土壤，污染土壤的鎘、鋅及鉛濃度分別為20、500及1,000 mg/kg，評估施用EDTA對於促進植生復育的效果，並以鎘、鋅及鉛濃度分別為10、100及1,000 mg/kg分別配製不同重金屬污染土壤，研究三種重金屬間交互作用對於植物累積重金屬的影響，並評估以相同的EDTA施加總量分一至四次施用對植物累積重金屬及降低地下水污染的風險的效果。
在鎘、鋅及鉛污染土壤中種植50天，五彩石竹地上部可累積高濃度的重金屬，鎘、鋅及鉛濃度約分別為80、3,700及220 mg/kg，因此可以應用於多種重金屬污染土壤的植生萃取(phytoextraction)。培地茅則可以在相同重金屬污染土壤中生長良好，並沒有受到重金屬的影響而產生毒害症狀，植物體地上部中鎘及鋅濃度分別約為40.7±8.28及1,399±132 mg/kg，而鉛濃度則未能檢出。印度芥菜則因土壤中存在多種重金屬毒害或重金屬污染濃度過高，導致生長不良。
施用5或10 mmol EDTA/kg可顯著增加種植五彩石竹土壤土壤溶液中鎘、鋅及鉛的濃度(p< 0.05)，五彩石竹地上部的鎘及鉛濃度也會因土壤溶液中重金屬濃度的增加而顯著增加(p< 0.05)，尤其以鉛的效果最顯著，10 mmol EDTA/kg可使五彩石竹地上部的重金屬濃度顯著上升至42.5±4.52 mg Cd/kg (1.67倍)、1,208±369 mg Zn/kg (1.74倍)及348±101 mg Pb/kg (33.1倍) (p< 0.05)。兩種濃度的EDTA處理都會極顯著增加植物地上部對鉛的總移除量(p< 0.001)，而對鎘和鋅而言，雖然施用EDTA會增加地上部的總移除量，但在統計上未達顯著差異，施用EDTA對於五彩石竹移除多種重金屬污染土壤中的鉛效果最好。施用EDTA可以顯著增加種植培地茅土壤土壤溶液中鎘、鋅及鉛的濃度(p< 0.05)，但培地茅地上部的鎘及鋅濃度僅在20-30及390-520 mg/kg間變化，此種培地茅品種地上部並不會累積鉛，儘管施用EDTA會降低植物的生質量及對重金屬的總移除量，但植物生長良好並不會因為土壤溶液中重金屬濃度增加而產生毒害症狀，因此培地茅可以應用於多種重金屬污染土壤的植生穩定(phytostabilization)。
在單一或多種重金屬處理土壤中施用2或5 mmol EDTA/kg可以顯著增加土壤溶液中的鎘、鋅、鉛、鐵及錳濃度(p< 0.05)，而土壤溶液中的鈣及鎂濃度則未出現顯著的變化，土壤中以去離子水可萃取的重金屬濃度也會因施用EDTA而顯著增加(p< 0.05)，而0.05M EDTA (pH 7.0)或0.005M DTPA (pH 5.3)兩種萃取法則是因為萃取能力較強，因此並無法區分出不同EDTA處理的效果，但兩種萃取法可萃取的重金屬濃度間具有良好的相關性。施用兩種濃度的EDTA都會顯著增加五彩石竹地上部的鎘及鉛濃度(p< 0.05)，尤其以鉛的效果最顯著。在4 mmol EDTA/kg的施用量下，多次低濃度的施用方式會降低重金屬對於五彩石竹的毒害，但EDTA不同施用方式並不會影響五彩石竹地上部的生質量、地上部的重金屬濃度及對於重金屬的總移除量，而以2 mmol/kg的施用量施用兩次則可以顯著降低土壤溶液中或去離子水可萃取的重金屬濃度，在本研究中，以2 mmol施用兩次的施用方式是可以降低對於地下水污染的衝擊。
污染土壤中的多種重金屬間存在不同的交互作用，而這種交互作用又會因為施用不同濃度的EDTA而產生改變。由五彩石竹地上部重金屬濃度及重金屬總移除量考量重金屬交互作用的結果發現，在未施用EDTA時，土壤施用鋅或鉛對於五彩石竹累積鎘為促進作用，土壤施用鎘對於五彩石竹累積鋅為抑制作用。當加入2 mmol EDTA/kg後，土壤施用鉛對於五彩石竹累積鎘為促進作用，土壤施用鋅對於五彩石竹累積鉛為促進作用。而施用5 mmol EDTA/kg後，除了土壤施用鎘或鋅對於五彩石竹累積鉛為抑制作用外，其餘重金屬間並無作用存在。
比較施用與不施用EDTA的試驗結果可知，五彩石竹地上部對於鎘及鋅的移除量以不施用EDTA直接種植在鎘、鋅及鉛污染土壤中50天最佳，對於鎘及鋅的總移除量分別為0.26及11.7 mg/plant，且重金屬不會因與EDTA錯合而使土壤溶液中的重金屬濃度劇烈增加。施用EDTA則可以增加五彩石竹地上部對於鉛的移除效果，對鉛的總移除量為1.37 mg/plant，鎘、鋅及鉛污染土壤中種植五彩石竹50天對於移除鎘及鋅及降低環境危害而言是較好的選擇。但如不考慮土壤溶液中重金屬濃度增加的風險，施用EDTA可以達到減少復育時間的目標。由於本研究所使用土壤的質地為坋質黏土，因此EDTA的推薦施用量為5 mmol/kg。

關鍵字

印度芥菜 ； 培地茅 ； 鎘 ； 植生萃取 ； 鋅 ； 植生穩定 ； 植生復育 ； 五彩石竹 ； 鉛

並列摘要

Heavy metals-contaminated soils can be remediated by phytoremediation techniques. Phytoextraction accumulated toxic metals from contaminated soil into the aboveground tissue of higher plants, which were then harvested and incinerated. Some synthetic chelating agents were applied to metal-contaminated soil to increase the mobility and bioavailability of the metal in the contaminated soils and also to increase the amount of heavy metals accumulated in the upper parts of plants. Rainbow pink (Dianthus Chinensis), Vetiver grass (Vetiver zizanioides), and Indian mustard (Brassica juncea) were used in this study to test the remediation of the Cd, Zn, and Pb-contaminated soil. The objectives of this study are to assess the effect of applying EDTA on the phytoremediation of metals-contaminated soils and to assess the interactions among three metals in multiple metals-contaminated soils. Different applying methods with same amounts of EDTA are also used in this study to assess their effect on the metal concentration in the shoot of plant and on reducing the potential risk of groundwater contamination.
Rainbow pink accumulated about 80 mg Cd/kg, 3700 mg Zn/kg, and 220 mg Pb/kg when it was grown in the Cd, Zn, and Pb-contaminated soil for 50 days. This plant can be used for phytoextraction of multiple metals-contaminated soils. Vetiver grass can grow well in the same concentrations of heavy metals-contaminated soil, and the growth was not affected by the toxicity of heavy metals. The concentrations of Cd and Zn in the shoots of vetiver grass were 40.7±8.28 and 1,399±132 mg/kg, respectively, and no Pb was detected. Because of the toxicity and high concentrations of multiple metals occurred in the soils, some damages were found in the growth stage of Indian mustard.
The concentrations of Cd, Zn, and Pb in soil solution were significantly increased after applying 5 or 10 mmol EDTA/kg (p< 0.05). The concentrations of Cd and Pb in shoot of rainbow pink were also significantly increased after EDTA treatments (p< 0.05), but it was not significantly increased for Zn. For biological uptake of metals in contaminated soil, the EDTA treatments only significantly increased the total uptake of Pb in the shoot of rainbow pink compared with the control treatment (p< 0.001), but it was not significantly increased for Cd and Zn uptake by rainbow pink. This indicated that the EDTA treatments could be evaluated as more efficient amendment method to remove the Pb from the contaminated soil. The results indicated that the concentrations of Cd, Zn, and Pb in the soil solution of vetiver grass were also significantly increased after applying EDTA treatments (p< 0.05), especially for applying 10 mmol EDTA/kg. Even the concentrations of the three metals in soil solution changed drastically, but the concentrations of Cd and Zn in the shoot of vetiver grass only varied from 20 to 30 mg Cd/kg and from 390 to 520 mg Zn/kg, respectively. The growth of vetiver grass was not affected by the toxicity of seriously contaminated metals. The applying of different concentrations of EDTA solution only slightly decreased the biomass of vetiver grass and slightly decreased the total removal of heavy metals from the contaminated soils. Applying 2 or 5 mmol EDTA/kg significantly increased the Cd, Zn, Pb, Fe, and Mn concentration in the soil solution of single- or multiple metals-contaminated soils (p< 0.05), but it had no significantly change on the concentration of Ca and Mg. Deionized water extractable metal concentrations are also significantly increased after applying EDTA (p< 0.05). Because of the strong extraction capacity of both 0.005M DTPA (pH 5.3) and 0.05M EDTA (pH 7.0), there was no significant increase on the metal concentration of two extractions methods after applying EDTA. There was no effect of single or multiple-dose application of 4 mmol EDTA/kg on biomass and total removal of heavy metals in shoots of rainbow pink. But the multiple-dose applying EDTA decreased the Cd, Zn, and Pb concentration in soil solution or extracted solution with deionized water, and thus reduced the risk of groundwater contamination.
There were some interactions among Cd, Zn, and Pb in the multiple metals- contaminated soils. The result of metals concentration and total removal in the shoots of rainbow pink showed that, without applying EDTA, adding Zn or Pb had enhancement effect on the uptake of Cd in the shoot of rainbow pink. The addition of Cd had inhibition effect on the uptake of Zn by rainbow pink. After applying EDTA, some interactions were found, and the addition of two concentrations of EDTA had greatest effect on the uptake of Pb by rainbow pink compared with the other elements.
In this study, planting rainbow pink in the Cd, Zn, and Pb-contaminated soil for 50 days without adding EDTA was the most economic and efficient method to remove Cd and Zn from contaminated soil compared with other treatments. The rainbow pink can accumulate high concentration of Cd and Zn in the shoots and remove the maximum amounts of these two elements (0.26 mg Cd/plant and 11.7 mg Zn/plant), and also had less risk on the pollution of the groundwater when comparing with other treatments. The addition of EDTA significantly increased the concentration and total removal of Pb in the shoots of rainbow pink, thus to reduce the remediation time. However, the application of EDTA was potential to pollute the groundwater. The result also indicated that 5 mmol EDTA/kg was recommended because the soil used in this study is a silty clay soil.

並列關鍵字

Indian mustard ； Pb ； vetiver grass ； rainbow pink ； phytostabilization ； Cd ； phytoextraction ； phytoremediation ； Zn

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