Effects of Increasing Dosages of Acid Mining Wastes in Metal Uptake by Lygeum spartum and Soil Metal Extractability酸性采矿废弃物添加量增加对 Lygeum spartum 金属吸收及土壤金属可提取性的影响

Héctor M. Conesa & Ahmad B. Moradi & Brett H. Robinson &

Francisco J. Jiménez-Cárceles & Rainer Schulin

Received: 7 November 2008 /Accepted: 12 January 2009 / Published online: 28 January 2009 # Springer Science + Business Media B.V. 2009

Abstract Mine tailings are an environmental problem in southern Spain because wind and water erosion of bare surfaces results in the dispersal of toxic metals over nearby urban or agricultural areas. Revegetation with tolerant native species may reduce this risk. We grew the grass Lygeum spartum under controlled conditions in pots containing a mine tailings mixed into nonpolluted soil to give treatments of 0%, 25%, 50%, 75%, and 100% mine tailings. We tested an acidic (pH 3) mine tailings which contained high concentrations of Cd, Cu, Pb, and Zn. Electrical conductivity and pH of the control soil were dramatically affected by the addition of the acid tailings (pH <4.5, electrical conductivity >2 dS m⁻¹ in all treatments). Water extractable metal concentrations increased in proportion to the amount of tailings added (up to 1,000 mg kg⁻¹ Zn). L. spartum survived, but only in the 25% treatment. In all treatments and for all metals, the plants accumulated higher concentrations in the roots than in shoots.

摘要 在西班牙南部，尾矿是一个环境问题，因为裸露表面受风蚀和水蚀作用，会导致有毒金属向邻近的城市或农业区扩散。利用耐性本土物种进行植被恢复可降低这一风险。本研究在可控条件下，将禾草 Lygeum spartum 种植于盆中，盆内为尾矿与未污染土壤的混合物，尾矿比例设为0%、25%、50%、75%和100%五个处理。供试尾矿为酸性（pH 3），含有高浓度的 Cd、Cu、Pb 和 Zn。添加酸性尾矿后，对照土壤的电导率和 pH 发生了显著变化（所有处理中 pH <4.5，电导率 >2 dS m⁻¹）。水提取态金属浓度随尾矿添加量成比例增加（Zn 最高达1,000 mg kg⁻¹）。L. spartum 仅在25%处理中存活。在所有处理中，各金属在植物根部的累积浓度均高于地上部。

_{H. M. Conesa} : _{A. B. Moradi} : _{B. H. Robinson} : _{R. Schulin} Institute of Terrestrial Ecosystems, ETH Zurich, Universitaetstrasse 16, 8092 Zürich, Switzerland

F. J. Jiménez-Cárceles BIOCYMA (Biología, Calidad y Medio Ambiente), Polígono Industrial La Serreta, Calle Ceuta 1, 30509 Molina de Segura, Murcia, Spain

H. M. Conesa (*) Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 30203 Cartagena, Spain e-mail: hectolines2001@yahoo.es

Keywords Phytostabilization . Phytomanagement . Mine tailings . Metal uptake . Metal tolerance

关键词 植物稳定；植物管理；尾矿；金属吸收；金属耐性

1Introduction引言

The disposal of mining wastes can have deleterious effects on the environment. Tailings often have a low pH, high concentrations of heavy metals, a lack of nutrients, a low water retention capacity, high electrical conductivity, and steep slopes. These factors inhibit plant establishment and, consequently, their surfaces are exposed to wind and water erosion, which may result in the contamination of nearby waters and soils with toxic metals. The dispersal of contaminants may occur on local as well as regional scales.

采矿废弃物的处置可对环境产生有害影响。尾矿通常具有 pH 低、重金属浓度高、养分缺乏、持水能力低、电导率高以及坡度陡等特点。这些因素抑制植物定植，因此其表面暴露于风蚀和水蚀之下，可能导致邻近水体和土壤受到有毒金属污染。污染物的扩散既可发生在局地尺度，也可发生在区域尺度。

Although natural revegetation of mine tailings is usually slow, a few species of metal and salt tolerant plants can survive in these extreme, but relatively competitor-free, environments (Macnair 1987). Annual species adapt faster to these conditions than perennial plants because their shorter life cycles allow them to produce a larger variety of genotypes in a shorter time (Wei et al. 2005).

尽管尾矿的自然植被恢复通常较为缓慢，但少数耐金属和耐盐植物能够在这种极端但竞争者相对较少的环境中存活（Macnair 1987）。一年生物种比多年生植物更快适应此类条件，因为其生命周期较短，可在更短时间内产生更多样的基因型（Wei et al. 2005）。

The Cartagena–La Unión mining district (0–400 m above sea level; 37°37′20″ N, 0°50′55″ W–37°40′03″

Cartagena–La Unión 矿区（海拔0–400 m；37°37′20″ N, 0°50′55″ W–37°40′03″

N, 0°48′12″ W) is at the Southeast of the Iberian Peninsula and covers an area of 50 km² (Fig. 1). The semiarid climate of the zone is typically Mediterranean with an annual rainfall of 250–300 mm. The annual average temperature is 18°C. Mining occurred in this area for more than 2,500 years until it ceased in 1991 for economic and environmental reasons. Base metals were smelted from sulfide minerals that included galena and sphalerite. The wastes form mining refining operations were stockpiled into tailings. These tailings pose a risk to local ecosystems and human health, due to the dispersal of dust and sediments by erosion (Conesa et al. 2006). Some are near urban and agricultural areas, increasing the risk of human exposure to metals via wind-borne dust or consumption of contaminated garden and agricultural crops.

N, 0°48′12″ W）位于伊比利亚半岛东南部，面积为50 km²（图1）。该区属典型的地中海型半干旱气候，年降水量为250–300 mm，年平均气温为18°C。该地区的采矿活动持续了2,500多年，直至1991年因经济和环境原因停止。贱金属由方铅矿和闪锌矿等硫化物矿物冶炼而得。采矿和精炼作业产生的废弃物被堆存为尾矿。由于侵蚀作用导致粉尘和沉积物扩散，这些尾矿对当地生态系统和人体健康构成风险（Conesa et al. 2006）。部分尾矿临近城市和农业区，增加了人体通过风载粉尘或食用受污染的园地及农田作物而暴露于金属的风险。

The aims of this work were to investigate the effect of increasing tailings dosages on metal solubility in an agricultural soil as well as the growth and metal uptake by a native grass species from the Cartagena– La Unión mining district.

本研究旨在探讨尾矿添加量增加对农业土壤中金属溶解度的影响，以及对 Cartagena–La Unión 矿区一种本土禾草生长和金属吸收的影响。

2Materials and Methods材料与方法

2.1 Soil Samples2.1 土壤样品

We studied the mine tailing called “Belleza”, located near La Unión (U.T.M. X688 760 m; Y4165 700 m; Z190 m). Conesa et al. (2006) describe the sampling locations and local vegetation. Tailing samples were taken from the upper 40 cm of 15 separate soil pits that were dug at regular intervals, at least 8 m apart. Then, all samples were mixed to give one homogenized composite sample which was air dried, sieved to <2 mm, and stored in plastic bags prior to laboratory analysis and pot experiment. Control soil was taken from a forest site near Zürich (Switzerland). Soil samples characteristics are shown in Table 1.

本研究以位于 La Unión 附近、名为“Belleza”的尾矿库为对象（U.T.M. X688 760 m；Y4165 700 m；Z190 m）。Conesa et al. (2006) 描述了采样位置和当地植被。尾矿样品采自按规则间距（间隔至少8 m）挖掘的15个独立土壤剖面的上层40 cm。随后，将全部样品混合成一个均质混合样，经风干、过2 mm筛后，装入塑料袋保存，用于实验室分析和盆栽试验。对照土壤采自瑞士苏黎世附近的一处林地。土壤样品性质见表1。

2.2 Metal Extractability Studies2.2 金属可提取性研究

Tailings and agricultural soil were mixed at different proportions to give treatments of 0% (uncontaminated soil), 25%, 50%, 75%, and 100% (pure mine tailings). For each mixture, we measured pH at a soil/water ratio of 1:2.5 using a Metrohm (Omega) pH meter. Total metal concentrations were determined by X-ray fluorescence spectroscopy (Spectro X-Lab 2000). Soluble metals were extracted with H2O at a 1:5 soil/water ratio (Ernst 1996). The filtered extracts were analyzed for Cu, Cd, Pb, Zn, K, Mg, Ca, and Na by flame atomic absorption spectrometry (SpectraAA 220/FS, Varian). Electrical conductivity was measured in the water extract (1:5 soil/water ratio) using a conductivity meter WTW LF318/SET.

将尾矿与农业土壤按不同比例混合，设置0%（未污染土壤）、25%、50%、75%和100%（纯尾矿）五个处理。对每种混合物，采用 Metrohm（Omega）pH 计在土水比1:2.5条件下测定 pH。全量金属浓度采用X射线荧光光谱法（Spectro X-Lab 2000）测定。可溶性金属以 H2O 按1:5土水比提取（Ernst 1996）。过滤后的提取液采用火焰原子吸收光谱法（SpectraAA 220/FS，Varian）测定 Cu、Cd、Pb、Zn、K、Mg、Ca 和 Na。水提取液（1:5土水比）的电导率采用 WTW LF318/SET 电导率仪测定。

2.3 Pot Experiment2.3 盆栽试验

The pot experiment was performed with a native grass, Lygeum spartum. Plants of this species were grown from seed in plastic pots containing approximately 0.4 kg of the aforementioned mine tailings– soil mixtures. We used seeds of L. spartum collected from the mining area of Cartagena–La Unión. Two seeds were planted in each pot. Pots were irrigated with nutrient solution containing 400 mM Ca(NO3)3 4H2O, 200 mM MgSO4 7H2O, 100 mM KH2PO4, and 500 mM KNO3 (all chemicals from Merck). Soils were maintained near field capacity by adding 100– 150 mL of solution per week. The plants were grown for 10 weeks in a climate chamber with a light cycle of 16:8 h light to dark under controlled humidity (50/ 90%) and temperature (16/23°C night/day).

盆栽试验采用本土禾草 Lygeum spartum 进行。该物种植株由种子在塑料盆中培育，每盆装有约0.4 kg上述尾矿–土壤混合物。所用 L. spartum 种子采自 Cartagena–La Unión 矿区。每盆播种两粒种子。盆栽以营养液灌溉，营养液含400 mM Ca(NO3)3 4H2O、200 mM MgSO4 7H2O、100 mM KH2PO4 和500 mM KNO3（所有化学品均购自 Merck）。每周添加100–150 mL溶液，使土壤保持在接近田间持水量的状态。植株在人工气候室中培养10周，光照周期为16:8 h（光照:黑暗），湿度（50/90%）和温度（夜/昼16/23°C）均受控制。

CEC cation exchange capacity, OC organic carbon, TN total nitrogen

CEC 阳离子交换量，OC 有机碳，TN 全氮

The plants were harvested in the 11th week of the experiment, washed with deionized water, and dried at 65°C for 72 h. Shoots and roots were separated. Dry weights were determined for individual plants. Samples (0.050–0.200 g) were digested in Teflon tubes with 15 mL HNO3 (65%) at 150°C for 1 h in a heating block DigiPREP MS (SCP Science). The digests were diluted to 20 mL with nanopure water. Copper, cadmium, lead, and zinc were measured by means of inductively coupled plasma optical emission spectrometry (Vista-MPX Varian). For quality assurance, we analyzed Certified Reference Material from the Community Bureau of Reference BCR No 62 (Olea europaea). We obtained recoveries of 80% for Pb and Cu and 90% for Zn.

植株于试验第11周收获，用去离子水洗净后，在65°C下烘干72 h。将地上部与根部分开，分别测定单株干重。样品（0.050–0.200 g）置于 Teflon 管中，加入15 mL HNO3（65%），在 DigiPREP MS 加热消解仪（SCP Science）中于150°C消解1 h。消解液用超纯水定容至20 mL。铜、镉、铅和锌采用电感耦合等离子体发射光谱法（Vista-MPX Varian）测定。为进行质量控制，分析了欧共体标准物质局（Community Bureau of Reference）的有证标准物质 BCR No 62（Olea europaea）。Pb 和 Cu 的回收率为80%，Zn 为90%。

We used SPSS 14.0.0 (SPSS, Chicago, IL, USA) for all statistical analysis (analysis of variance with least significant difference). Data that were lognormally distributed according to the Levene test were log-transformed before analysis. Differences at P<0.05 level were considered significant.

所有统计分析均采用 SPSS 14.0.0（SPSS, Chicago, IL, USA）进行（方差分析及最小显著差数法）。经 Levene 检验呈对数正态分布的数据在分析前进行对数转换。以 P<0.05 水平的差异视为显著。

3Results and Discussion结果与讨论

The addition of acid tailings material to the control soil significantly reduced the pH (from 7 to 4.2) already in the 25% treatment rate. All the mixtures with mine tailings had electrical conductivity values

在对照土壤中添加酸性尾矿物料后，pH 在25%处理中即已显著降低（由7降至4.2）。所有含尾矿的混合物的电导率值均

>2 dS/m (Table 2) and are thus extremely saline according to the classification of Alarcón-Vera (2004). Only salt tolerant species are able to grow under such conditions and one would expect that chickpeas, which are sensitive to salinity, would show reduced growth in the treatments with mine tailings.

>2 dS/m（表2），因此按照 Alarcón-Vera (2004) 的分类属于极度盐渍化。只有耐盐物种能够在此条件下生长，可以预期对盐分敏感的鹰嘴豆在含尾矿的处理中生长会受到抑制。

The addition of tailing material to the control soil caused significant increases in extractable heavy metal concentrations (Fig. 2a). Some 20% of the total Zn and 60–90% of total Cd was water soluble in all acid tailing treatments. The water extractability of Pb and Cu increased in proportion to the percentage of tailing material added. The maximum values were 2% and 0.15%, respectively, in the 100% treatment. Water extractable Na concentrations were not affected by acid tailing addition (Fig. 2b), while soluble Ca and Mg concentrations increased significantly.

在对照土壤中添加尾矿物料使可提取重金属浓度显著增加（图2a）。在所有酸性尾矿处理中，约20%的全量 Zn 和60–90%的全量 Cd 为水溶态。Pb 和 Cu 的水提取率随尾矿物料添加比例成比例增加，在100%处理中分别达到最大值2%和0.15%。水提取态 Na 浓度不受酸性尾矿添加的影响（图2b），而可溶性 Ca 和 Mg 浓度显著增加。

According to European legislation (European Communities Council 1986), the addition of the tailings materials used in this study to agricultural soils would be forbidden, because the metal concentrations exceeded limit values (>4,000 mg kg⁻¹ Zn; >1,200 mg kg⁻¹ Pb). Although at first view a mixture of 25% or 50% tailing with the surrounding soil may appear unlikely, some previous studies in the area have found that due to deposition of wind-eroded material, more than 50% of tailing materials had been incorporated into soil profiles of lands surrounding the tailings (García-García 2004).

根据欧洲法规（European Communities Council 1986），本研究所用尾矿物料因金属浓度超过限值（Zn >4,000 mg kg⁻¹；Pb >1,200 mg kg⁻¹）而禁止施用于农业土壤。尽管乍看之下，25%或50%的尾矿与周边土壤混合的情形似乎不太可能出现，但该地区此前的一些研究发现，由于风蚀物料的沉降，尾矿周边土地的土壤剖面中已混入超过50%的尾矿物料（García-García 2004）。

The ratios of exchangeable Ca/Mg and K/Mg ratios were within the normal range in soils, indicating that neither excess nor deficiencies should occur. According to Alarcón-Vera (2004), ratios of exchangeable Ca/Mg (in meq 100 g⁻¹) around 5 are ideal for healthy plant growth. If this ratio is <1, deficiencies of Ca may occur and if it is >10, then deficiencies of Mg may take place. Following this criteria, our control soil had deficiencies of Mg (ratio Ca/Mg >10), while all the treatments with acid tailing had deficiency of Ca (ratio Ca/Mg <1). Furthermore, Alarcón-Vera (2004) considers ratios of K/Mg (in meq 100 g⁻¹) below 0.2 as an indicator of K deficiencies. In all the treatments except the control soil, the K/Mg ratio was 0.4 and thus above this value. For K, solubility increased in the 25% treatment compared to the control, then decreased at higher rates of mine tailing additions. Total K in control soil is 14,000 mg kg⁻¹ while in acid tailing is 2,000 mg kg⁻¹ (data not shown). The addition of acid tailing enhanced mobility of K due to acidification in the 25% treatment. Further addition of acid tailing decreased of the pool of total K and consequently the water extractable concentrations were lower. Calcium and magnesium increased significantly as mine tailing is added. This may be produced by higher cation availability in the control soil as pH decreases and the high content of these two cations in the tailing soil.

交换性 Ca/Mg 和 K/Mg 比值处于土壤正常范围内，表明不应出现过量或缺乏。根据 Alarcón-Vera (2004)，交换性 Ca/Mg 比值（以 meq 100 g⁻¹ 计）约为5时最有利于植物健康生长；若该比值 <1，可能出现 Ca 缺乏；若 >10，则可能出现 Mg 缺乏。按照这一标准，本研究的对照土壤存在 Mg 缺乏（Ca/Mg 比值 >10），而所有酸性尾矿处理均存在 Ca 缺乏（Ca/Mg 比值 <1）。此外，Alarcón-Vera (2004) 将 K/Mg 比值（以 meq 100 g⁻¹ 计）低于0.2视为 K 缺乏的指标。除对照土壤外，所有处理的 K/Mg 比值均为0.4，高于该值。K 的溶解度在25%处理中较对照有所增加，随后在更高尾矿添加量下降低。对照土壤中全 K 为14,000 mg kg⁻¹，而酸性尾矿中为2,000 mg kg⁻¹（数据未列出）。在25%处理中，酸化作用使酸性尾矿的添加提高了 K 的迁移性。进一步添加酸性尾矿则降低了全 K 库，因而水提取态浓度较低。随着尾矿添加量增加，钙和镁显著增加。这可能是由于 pH 降低时对照土壤中阳离子有效性提高，以及尾矿土壤中这两种阳离子含量较高所致。

Values in brackets are standard deviation of three replicate treatments EC electrical conductivity ^{a Geometric} mean. The differences between the samples were <0.1, the detection limit of our apparatus

括号内数值为三次重复处理的标准差。EC 电导率。^{a 几何}平均值。样品间差异 <0.1，即本仪器的检出限

L. spartum plants died in 50%, 75%, and 100% tailing treatments and only those in the 25% treatment showed signs of growth. These plants (Fig. 3) had higher Pb (100 mg kg⁻¹ in shoots; 800 mg kg⁻¹ in roots) and Zn (1,000–1,800 mg kg⁻¹ in shoots, up to 3,500 mg kg⁻¹ in roots). Differences were larger between controls and acid tailing treatments than among the various acid tailings treatments possibly because of having reached in the latter one the phytotoxic levels. Conesa et al. (2006) reported levels ∼150 mg kg⁻¹ for Zn, ∼50 mg kg⁻¹ for Pb, and ∼5 mg kg⁻¹ for Cu in Pipthaterum miliaceum and L. spartum plants growing in situ in tailings from the Cartagena–La Unión mining area. These concentrations were lower than the values obtained in our study (even in relation to the lowest polluted treatment). Conesa et al. (2007) showed how the growth of certain plant species under controlled conditions resulted in significantly higher metal uptake compared to plants sampled in the field due to the changes in growing conditions. These changes were especially important when plants from arid environments are oversupplied with water.

L. spartum 植株在50%、75%和100%尾矿处理中死亡，仅25%处理中的植株表现出生长迹象。这些植株（图3）具有较高的 Pb（地上部100 mg kg⁻¹；根部800 mg kg⁻¹）和 Zn（地上部1,000–1,800 mg kg⁻¹，根部最高达3,500 mg kg⁻¹）浓度。对照与酸性尾矿处理之间的差异大于各酸性尾矿处理之间的差异，这可能是因为后者已达到植物毒性水平。Conesa et al. (2006) 报道，在 Cartagena–La Unión 矿区尾矿上原位生长的 Pipthaterum miliaceum 和 L. spartum 植株中，Zn 约为150 mg kg⁻¹，Pb 约为50 mg kg⁻¹，Cu 约为5 mg kg⁻¹。这些浓度低于本研究所得数值（即使与污染最轻的处理相比亦是如此）。Conesa et al. (2007) 表明，由于生长条件的改变，某些植物物种在可控条件下生长时的金属吸收量显著高于田间采集的植株。当干旱环境植物被过量供水时，这些变化尤为重要。

Cattle should be prevented from grazing on L. spartum growing on soils affected by deposition of mine tailings material. Although the concentrations of metals taken up through roots and accumulated in plant tissues are low, metal-rich dust particles adhering to the surfaces of plants must also be taken into account. Furthermore, factors such as the direct ingestion of soil by cattle may play an important role for the transfer of the metals into the food chain.

应禁止牛只在受尾矿物料沉降影响的土壤上放牧采食 L. spartum。尽管经根系吸收并累积于植物组织中的金属浓度较低，但仍须考虑附着于植物表面的富含金属的粉尘颗粒。此外，牛只直接摄食土壤等因素可能在金属向食物链转移过程中发挥重要作用。

4Conclusions结论

Adding mine tailings to nonpolluted soil affects soil properties, plant growth, and metal accumulation by plants differed. Acid mine tailings addition had a greater affect on soil properties (pH, electrical conductivity) and inhibited plant growth in all treatments except at 25% dosage.

在未污染土壤中添加尾矿会影响土壤性质、植物生长以及植物的金属累积。添加酸性尾矿对土壤性质（pH、电导率）的影响更大，并且除25%添加量外，在所有处理中均抑制了植物生长。

Our experiment indicate that L. spartum grow in polluted mine tailing polluted soils and accumulate high concentrations of metals without being showing visible symptoms under low dosages of polluted tailings. Therefore, plant metal uptake may pass unnoticed by farmers and constitute risk for food chain. On the other hand, revegetating bare mine tailings is important to stabilize the surfaces of these polluted soils and to reduce the migration of polluted materials to the adjacent fields. Future scientific studies could investigate soil amendments that decrease metal bioavailability in polluted areas near tailings.

本试验表明，在低添加量污染尾矿条件下，L. spartum 能够在受尾矿污染的土壤中生长，并累积高浓度金属而不表现出可见症状。因此，植物对金属的吸收可能不为农民所察觉，从而对食物链构成风险。另一方面，对裸露尾矿进行植被恢复对于稳定这些污染土壤表面、减少污染物料向邻近农田迁移具有重要意义。未来的科学研究可探讨能够降低尾矿附近污染区域金属生物有效性的土壤改良剂。

Acknowledgments We thank Anna Grünwald and René Saladin for their technical assistance. Also, we want to thank Dr. Ripolles by his technical assessment. This work was supported by a postdoctoral grant from the “Fundación Séneca” of the Comunidad Autónoma de la Región de Murcia for Dr. Héctor M. Conesa.

致谢 感谢 Anna Grünwald 和 René Saladin 提供的技术协助，并感谢 Ripolles 博士的技术评估。本研究由 Comunidad Autónoma de la Región de Murcia 的“Fundación Séneca”向 Héctor M. Conesa 博士提供的博士后资助支持。

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