RESEARCH ARTICLE

Shi Yakun1& Mu Xingmin1,2

& Li Kairong3 & Shao Hongbo4,5

Received: 9 December 2015 /Accepted: 7 March 2016 /Published online: 30 March 2016# Springer-Verlag Berlin Heidelberg 2016

Abstract Soil contamination by heavy metals in coal minewastelands is a significant environmental issue in most devel-oping countries. The purpose of this study is to evaluate con-tamination characteristics in the coal mine wastelands ofSanlidong coal mine, Tongchuan, China. To achieve this goal,we conducted field sampling work, followed by further anal-ysis of the properties of soil contamination and accumulationcharacteristics in woody plants. At this site, the pH valueranged from 4.41 to 7.88, and the nutrient content of the soilrose gradually with the time after deposition due to theweathering effect improving the soil quality. Meanwhile, thelevels of Cd, Cr, Cu, Ni, and Zn gradually decreased with thepassage time. Generally, heavy metal contamination wasfound to be more serious in the discharge refuse area, withCd contamination at moderate or heavy levels; Ni, Zn, and Cucontamination at light levels; and with no Cr contamination.

The geoaccumulation index (Igeo) was highest for Cd (2.38–3.14), followed by Ni, Zn, Cu, and Cr. Heavy metals accumu-lated on the lower slopes and spread to the surrounding areasvia hydrodynamic effects and wind. According to transfer andenrichment coefficient analyses, Robinia pseudoacacia,Ulmus pumila, and Hippophae rhamnoides with considerablebiomass could be used as pollution-resistant tree species forvegetation restoration. This study provided a theoretical basisfor the restoration of the ecological environment in the miningarea. This report described a link between heavy metal con-tamination of soils and growth dynamics of woody plants inChina.

Keywords Coal ganguewasteland . Heavymetal .

Geoaccumulation index . Accumulation characteristic .

Woody plant

Introduction

Coal is an important mineral resource that provides eco-nomic benefits, but it also causes many environmentalproblems (Bhuiyan et al. 2010; Fan et al. 2003; Galuninet al. 2014). The creation of wastelands caused by mininghas garnered significant attention in China and worldwide.According to statistics, coal gangue comprises appropri-ately 70 % of the wasteland backfill in China (Li 2008).The accumulation of coal gangue has brought a variety ofenvironmental and social problems such as land occupa-tion, landscape destruction, and, specially, heavy metalpollution (Ao and Huang 2005). Because of weatheringand decomposing, water containing heavy metal elementsis leached into the soil. Heavy metal pollution in the soilaround coal gangue dumps is a threat to human healthbecause it can be easily transferred into the human body

Responsible editor: Elena Maestri

* Mu Xingminxmmu@ms.iswc.ac.cn

* Shao Hongboshaohongbochu@126.com

1 Institute of Soil andWater Conservation, Northwest A&FUniversity,Xinong Road 26, Yangling 712100, Shaanxi, China

2 Institute of Soil and Water Conservation, Chinese Academy ofSciences and Ministry of Water Resources, Yangling 712100, China

3 College of Natural Resource and Environment, Northwest A&FUniversity, Yangling 712100, China

4 Institute of Agro-biotechnology, Jiangsu Academy of AgriculturalSciences, Nanjing 210014, China

5 Yantai Institute of Coastal Zone Research, Chinese Academy ofSciences, Yantai 264003, China

Environ Sci Pollut Res (2016) 23:13489–13497DOI 10.1007/s11356-016-6432-8

Soil characterization and differential patterns of heavy metalaccumulation in woody plants grown in coal ganguewastelands in Shaanxi, China

through ingestion via the hand-to-mouth pathway, inhala-t ion, and dermal contact (Yeganeh et al . 2013) .Additionally, the long-term accumulation of heavy metalelements could result in a decreased buffering capacity ofsoil, threatening the ecological environment. The emissionbehaviors of toxic elements during coal mining, transpor-tation (Lough et al. 2005; Shafer et al. 2011), combustion(Querol et al. 1995; Yi et al. 2008), and waste disposal(Gidarakos et al. 2009; Zhang et al. 2008a) have receivedintensive study. However, the investigations of soil con-taminated by heavy metal in coal mine wastelands duringthe long-term dumping of coal gangue are extremelyscarce.

Current research on coal gangue focuses mainly on thecontamination of coal gangue in the surrounding tailings,soil, and groundwater, as well as on the chemical specia-tion of heavy metals with obvious seasonal changes indistribution (Liu et al. 2003). The degree of heavy metalcontamination in coal mine wastelands varies according tothe geological conditions in the mining areas and the man-ner of disposal. Many researchers have performed relatedstudies on soil properties and contaminated characteristicsanalysis. However, the most attention has been paid to thepH value in different locations and its relationship withheavy metals. For instance, the pH value (ranging from5.48 to 7.91) is inversely proportional to the distance tothe coal gangue dump (Jiang et al. 2014). Some heavymetals can enter the human body via the food chainthrough the soil–plant system, causing harm to people’shealth. However, given the huge coal gangue discharges,the area of coal gangue piles around the coal mines rangesfrom thousands to tens of thousands of square meters.Under the effects of long-term weathering and leaching,those piles become covered with primary weathering soil,which is suitable for some plants to grow. Minimal re-search has been conducted on the contamination of soilfrom weathered coal gangue piles, so an investigationand screening of the primary plants growing on such pilescould provide the basis for phytoremediation technology,which is the research focus of contaminated siteremediation.

With the Sanlidong coal mine as an example, thisstudy investigated heavy metal contamination ofweathering soil on the surface of large mine tips andthe accumulation characteristics of the primary woodyplants in this area. The present work described the con-ducted investigation, field sampling, laboratory experi-ment, and mathematical analysis. A comprehensivestudy was conducted to screen pollution-resistant treespecies with strong enrichment ability of heavy metals,and to provide a scientific basis for polluted soil treat-ment and ecological restoration in the coal ganguedumping field.

Materials and methods

Study area

The Yintai District, Tongchuan County, China, permittedthe field study. Located in the middle of Shaanxi Provinceand on the southern margin of the Loess Plateau at 108°34′ to 109° 29′ E and 34° 50′ to 35° 34′ N, Tongchuan Cityhas a warm temperate continental monsoon climate withfrequent frosts, rainstorms, droughts, and other severeweather conditions. The area has an annual precipitationbetween 589 and 650 mm. The average amount of sun-shine is 2345.7 h, and the annual average temperature isbetween 10 and 11 °C. The frost-free period lasts for 160–219 days. The extreme maximum temperature is 34.3 °C,and the extreme minimum temperature is −21.1 °C. Thestudy area is in Yintai District, with an area of 70,000 m2

(Fig. 1). It has the approximate shape of a parallelogramwith an elevation of 1017 m at the top and 881 m at thebottom, lower descending from north to south. This sitecontains seven coal gangue piles, covering an area of ap-proximately 25,695 m2, and two loess terraces, coveringan area of approximately 3700 m2. The average height ofcoal gangue piles is 36 m. In some regions where theslopes are greater than the natural repose angle, collapseand soil erosion frequently occur. Coal gangue is piledlayer by layer with the age of the deposits piling yearsranging from more than 40 years at the bottom to only8 years on the surface. The natural vegetation on theweathering soil is well restored, with loosely scatteredherbs, shrubs, and arbores.

Field sampling of soil and plant

Samples were obtained using the average distribution methodand grid distribution method. Given the complex and variedterrains in the discharge refuse area, 45 sampling points wereset according to the dumping year and site conditions. Twelvepoints were distributed in four lines (three points in each sam-pling line) in four directions around the discharge refuse areabased on the predominant wind direction (northwest wind),terrain, channel trend (from west to east), and other factors.The distance between two adjacent sampling points in thesame line was approximately 200–400 m. In addition, fourblank matching points were distributed in the pollution-freeand nonagricultural area (CK sampling area) around the min-ing area. From each sample site, five random soil subsampleswere taken using a stainless steel spatula from the top 20-cmdepth (because soil texture of the weathering coal gangue wasvery tight and hard) and mixed thoroughly. After air-drying(natural air-drying or freeze-drying) of the collected soil sam-ples, stones and animal and plant residues were removed fromthe samples. The soil was crushed with a stick (or agate rod),

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screened through a 0.25-mm nylon sieve, mixed well, tightlyclosed, and then stored.

Based on the field survey, the coal gangue dumping fieldwas divided into five typical sections according to the terrainof the coal gangue wastelands, dumping year, and plant dis-tribution, and with reference to the partition of the soil samplesto study the primary woody plant biomass and cumulativecharacteristic of heavy metals. In this study, woody plantswere divided into two categories, shrubs and arbores (trees).For shrubs, the quadrat was set according to the actual situa-tion: 1×1 m quadrat for evenly distributed plants and 1×2 mquadrat for unevenly distributed plants. Five quadrats were setrandomly in each section, for a total of 25 quadrats. The name,variety, and coverage of plants in each section were identified.The stems, leaves, and roots of the typical plants that grewwell in large quantities, as well as the root soil, were collectedto reap the aboveground plant part in each section andweighed to calculate the biomass. For arbores, the name andvariety were recorded. Leaves, branches, roots, and root soilwere collected, and the biomass per tree of each tree specieswas weighed. The samples were brought to the laboratory tocalculate the biomass and determine the contents of heavymetals. The plant samples were cleaned and dried at 80 °Cto weigh the dry weight of the aboveground part. The rootsand aboveground part of shrubs (mixing branches, barks, and

leaves) were cut. The leaves, branches, and roots of arboreswere cut and then crushed to 0.25-mm powders with a crusher.Finally, the powders were tightly closed and stored.

Laboratory measurements of heavy metal content

The soil samples were digested using HF-HNO3-H2SO4-HClO4, and heavy metal (Cd, Cr, Cu, Ni, and Zn) contentswere determined using an atomic absorption spectrophotom-eter (Bao 2000; China 1997). The plant samples were digestedusing HNO3-HClO4, and heavy metal (Cd, Cr, Cu, Ni, andZn) contents determined using an atomic absorption spectro-photometer (Bao 2000). Three groups of parallel tests wereperformed with a blank control for each sample to control therelative error within 5 %.

Quantitative indices for heavy metal soil contamination

The geoaccumulation index (Igeo) was proposed by theGerman scientist Müller (it is also known as theMuller index).It is widely used as a quantitative index for the degree of theheavy metal contamination in the deposit or other materials(Förstner and Müller 1981; Muller 1969). This method con-siders not only the man-made contamination factors and en-vironmental geochemical background value difference but

Fig. 1 Study areas and sampling locations of Sanlidong coal in Shaanxi Province, China

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also the change in the background value caused by naturaldeposit diagenesis and other geological processes (Chaiet al. 2006). The formula is as follows:

Igeo ¼ log2Ci

1:5� BEi

� �; ð1Þ

where Ci refers to the content of element i in the sample, andBEi is the geochemical background value of element i. In thispaper, the control soil of Tongchuan (i.e., the CK area) wasused as the background value; the modified index was 1.5,which was used to characterize the deposition feature, rockgeology, and other effects. The geoaccumulation index eval-uation standard is shown in Table 1 (Förstner et al. 1990).

The transfer factor (TF) refers to the ratio of the content of aheavy metal in the aboveground part of a plant to that in theroot, reflecting the ability of the plant to transfer the heavymetal from the root to the aboveground part of the plant (Heet al. 2013).

The bioaccumulation factor (BF) refers to the ratio of thecontent of a heavy metal in the plant to that in the soil,reflecting the plant’s ability of to absorb the heavy metal(Fayiga et al. 2004).

Quality control and statistical analyses

All experiments were performed in triplicate. Reagent blankswere used to correct the analytical values. Standard referencematerials for wheat (GBW10011) and soil (GBW07405) wereobtained from National Research Center of CertifiedReferenceMaterials (Beijing, China); the recovery of the stan-dard samples ranged from 96.2 to 104.6 %. To simulate thedistribution of heavy metal contamination in the study area,BKriging^ interpolation calculation was applied when plottingthe contour map. All results were statistically analyzed usingIBM SPSS Statistics 22.0. Differences among different sam-ples were compared by one-way ANOVA followed by aTukey’s test.

Results and discussion

Properties of soil contaminated with heavy metal

The basic physical and chemical properties of soil from theweathered coal gangue piles had a great influence on the trans-fer of heavy metals. According to Table 2, with the increase inthe number of years after dumping, the weathering effect im-proved the soil quality leading to gradual increases in thesurface soil moisture content. However, the weathering effectof the soil was still smaller than that in the CK area. The soilmoisture content in the middle of slopes was affected by grav-ity and rainfall–runoff scour and was therefore smaller thanthat in the lower slopes. With the increase in the number ofyears after dumping, soil maturation was enhanced. Areas 1,2, and 3 had more recent dumping and consisted of sandy soil,whereas the older areas 4 and 5 consisted of loamy soil, whichwas more suitable for plant growth. However, the level of soilmaturation in the discharge refuse area was low. The pH levelof the soil rose gradually with the increase in the number ofyears after dumping. In the same research area, the pH level inthe upper slopes was greater than that in the middle and lowerslopes. The pH level in the inner side of the terrace was greaterthan that in the central terrace and outer side. The total amountof water-soluble salts decreased gradually with the increase inthe number of years after dumping. In addition, the totalamount of water-soluble salts transferred from top to bottomand from inside to outside increased. In other words, thewater-soluble salts content in the lower slopes and outer sideof the terrace was high. In the areas with more recent dumping(areas 1 and 2), the soil lacked organic matter and seriouslylacked the nutrient elements of N, P, and K. In the areas withlonger time since dumping (areas 3, 4, and 5), the nutrientcontent increased gradually, which was mainly reflected inthe rich organic matter content and normal contents of ammo-nium, nitrate, and available potassium. These findings indicatethat vegetation was restored well and the soil nutrients in-creased in the areas with long dumping years.

Distribution of heavy metal contents in soils

The main contaminants in the discharge refuse area were theheavy metals in the soil and water near the coal gangue pile.Table 3 shows that the heavy metal content in the dischargerefuse area was obviously greater than that in the environmen-tal background: The Cd content in five study areas was 8–14times more than that in the CK area, the content of Cu and Crwas 1–2 times more than that in the CK area, and the contentof Ni and Zn was 2–3 times more than that in the CK area.

With the increase in the time since dumping, the content ofheavy metals showed a downward trend, and the change in thelevels of Cu, Cd, and Zn was the most prominent; the contentof Ni showed a weak fluctuation. The results show that the

Table 1 Geoaccumulation index and classification of contaminationlevel

Contamination degree Igeo Contamination level

0 Igeo < 0 No contamination

1 0 < Igeo ≤ 1 Light contamination

2 1 < Igeo ≤ 2 Slightly moderate contamination

3 2 < Igeo ≤ 3 Moderate contamination

4 3 < Igeo ≤ 4 Slightly heavy contamination

5 4 < Igeo ≤ 5 Heavy contamination

6 Igeo > 5 Extremely heavy contamination

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longer the time since dumping, the more the coal gangue wasweathered and the more eluviation through runoff, allresulting in the decreasing of heavy metal content in the top-soil. In addition, the physicochemical properties of the weath-ered soil on the surface of coal gangue improved, and thevegetation coverage increased gradually. The plants had theperfect purifying effect on heavy metals, so the content ofheavy metals decreased with time.

Heavy metals presented certain distribution patterns underdifferent terrain conditions. On slopes, heavy metals graduallymigrated to the lower slopes with the washing and leaching,leading to a higher content of heavymetals on the lower slopesthan that on the upper slopes. In the terrace, the distribution ofheavy metals had no obvious pattern because of the compli-cated conditions of the surface and great man-madedisturbances.

The channel of the Sanlidong coal mine is oriented in aneast–west direction. According to Fig. 2, the distribution ofheavy metals was significantly affected by the channel orien-tation and terrace. At the upper stream of the channel, thewestern area was higher than the eastern area, so precipitationand surface soil moisture flowed or transferred from west toeast. Overall, the content of heavy metals in the eastern areawas higher than that in the western area. In addition, the heavymetal content decreased gradually with the increase in dis-tance from the discharge refuse area. The heavy metal contentwas highest in the discharge refuse area. Thus, heavy metal

contamination in the areas around the discharge refuse areawas greatly affected by the scouring and leaching of heavymetals in the discharge refuse area from surface water andrains. However, in the transfer process, given the self-purification and dilution effect of vegetation and soil, theheavy metal content in soil gradually decreased with the in-crease in distance from the discharge refuse area and resultedin weak or no contamination.

The wind blows from the northwest in the study area. Itpasses through the farmland soil, windbreak forest, dischargerefuse area, barrage, and residential area. Given the existenceof the windbreak forest and barrage, heavy metal contamina-tion of the discharge refuse area to the surrounding soil waslight (Fig. 2). Because of these man-made factors, the transferof heavy metals was controlled. Thus, macroscopically, heavymetal contamination on the edge of the windbreak forest in-creased closer to the discharge refuse area, but it was at thesafety level. The heavy metal content was the highest in thedischarge refuse area. The heavy metal content in the residen-tial area on the south of the barrage was reduced sharply andreached normal levels because of the existence of the barrage.The heavy metal content also showed a downward trend withthe increase in distance from the discharge refuse area.Overall, a state free of contamination was observed.

In contrast to the results of the current study, research find-ings by Zhang which focused on a coal mine area in Hongguin the Loess Plateau showed that the content of heavy metals

Table 3 Heavy metal content inthe discharged refuses area (mg/kg) Sampling site Cd Cr Cu Ni Zn

Area 1 1.28a (0.08) 91.0a (13.2) 40.7a (9.93) 66.6a (6.93) 146a (15.8)

Area 2 1.17a (0.19) 92.6a (26.8) 38.3a (8.47) 59.3a (27.1) 127ab (15.7)

Area 3 0.88ab (0.27) 84.6ab (1.83) 36.5a (8.07) 64.0a (1.42) 103abc (5.90)

Area 4 0.88ab (0.13) 75.5b (26.9) 34.3ab (5.61) 59.6a (2.77) 95.5bc (42.2)

Area 5 0.76b (0.44) 71.3b (18.7) 27.1c (7.48) 48.4ab (10.6) 52.5c (7.92)

Control 0.10ab (0.04) 59.8c (19.9) 18.3c (6.08) 26.8b (8.94) 51.3c (17.1)

The mean value with three replicates is shown, with the standard error in parentheses. Plots that were notsignificantly different with respect to metal concentration (P> 0.05, one-way analysis of variation with LSD test)are marked with the same letter in superscript

Environ Sci Pollut Res (2016) 23:13489–13497 13493

Table 2 Physiochemical properties of different soils

Samplingsite

Moisture contents (%)

Soil bulk density(g/cm3)

Soiltexture

pH Organic matter(g/kg)

Total nitrogen(g/kg)

Total phosphate(g/kg)

Total potassium(g/kg)

Area 1 5.65c (0.73) 1.52a (0.09) Sandy soil 4.41c (0.28) 9.92de (1.23) 0.23c (0.14) 0.13c (0.04) 4.53c (2.44)

Area 2 7.36bc (0.55) 1.49a (0.10) Sandy soil 4.60c (0.27) 14.2d (1.18) 0.20c (0.13) 0.18bc (0.11) 7.42bc (3.52)

Area 3 8.24b (0.37) 1.37ab (0.13) Sandy soil 6.38bc (0.79) 57.5c (5.96) 0.35bc (0.15) 0.20b (0.07) 12.8ab (1.97)

Area 4 9.46ab (0.32) 1.24ab (0.21) Loam soil 7.15b (0.13) 98.9b (5.32) 0.53ab (0.04) 0.33ab (0.12) 15.5a (2.13)

Area 5 11.56a (0.44) 1.19a (0.09) Loam soil 7.88a (0.05) 169a (11.3) 0.52ab (0.09) 0.34ab (0.09) 18.2a (3.58)

Control 10.83ab (0.17) 1.29ab (0.07) Loam soil 7.98a (0.09) 113b (10.2) 0.72a (0.24) 0.51a (0.17) 17.7a (5.91)

The mean value with three replicates is shown, with the standard error in parentheses. Plots that were not significantly different with respect to metalconcentration (P> 0.05, one-way analysis of variation with LSD test) are marked with the same letter in superscript

in the soil near the coal gangue powder pile was higher thanthat in the coal gangue pile because fine coal powders canenter and concentrate in the soil more easily than coal gangue(Zhang et al. 2008b). The difference in results may be due tothe differences in wind direction and terrain of the study area.Heavy metal contamination of the soil from the areas aroundthe discharge refuse field was caused by three factors: channelorientation (or hydrodynamic direction), wind direction, anddifferent land uses. For channel orientation (or hydrodynamicdirection), the heavy metals were mitigated with rainfall andsurface soil moisture as carriers, and they entered the soil andwater, resulting in heavy metal contamination. For wind-borne materials, fly ash was an important cause of heavymetalcontamination. It was carried to the surrounding areas by thewind with different degrees of contamination depending onwind direction. The heaviest levels of contamination weredownwind. For different land uses, the soil conditions andtypes in the areas around the discharge refuse field were com-plicated because of the influence of man-made factors.

The use of land for farmland, vegetation restoration, indus-try, and other human activities all had a significant impact onthe distribution of heavy metal contaminants.

Quantifying heavy metal contamination in soil

According to Table 4, Cd contamination was the mostserious in the discharge refuse field, with an averagecontent of 0.99 mg/kg and Igeo of 2.77, reaching level3 (moderate contamination). In areas 1 and 2, the Igeovalues were 3.14 and 3.01, respectively, reaching level 4(slightly heavy contamination). In areas 3, 4, and 5, theIgeo values were between 2.38 and 2.60, reaching level3 (moderate contamination). It was followed by Ni con-tamination, with Igeo of 0.27–0.73 in five study areas,reaching level 1 (light contamination). Zn contaminationwas light, with an average content of 104.88 mg/kg andIgeo of 0.45, reaching level 1 (light contamination). Fourstudy areas reached level 1 (light contamination), and

Table 4 Igeo and pollution degreeof heavy metal in differentsampling sites

Sampling sites Cd Cr Cu Ni Zn

Igeo Level Igeo Level Igeo Level Igeo Level Igeo Level

1 3.14 4 0.02 1 0.57 1 0.73 1 0.93 1

2 3.01 4 0.05 1 0.48 1 0.56 1 0.72 1

3 2.6 3 −0.08 0 0.42 1 0.67 1 0.42 1

4 2.6 3 −0.25 0 0.32 1 0.57 1 0.31 1

5 2.38 3 −0.33 0 −0.01 0 0.27 1 −0.55 0

Average 2.77 3 −0.11 0 0.37 1 0.57 1 0.45 1

The mean value with three replicates is shown

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Fig. 2 Distribution of heavy metal contamination in the study area

area 5 was at level 0 (no contamination). Cu contami-nation was light, with five study areas at level 1 (lightcontamination). The Cr content was higher in areas 1and 2, reaching level 1 (light contamination), but low inareas 3, 4, and 5 without contamination. The order ofthe heavy metal contamination degree from heavy tolight was Cd, Ni, Zn, Cu, and Cr.

Heavymetal accumulation characteristics in woody plants

This study mainly focuses on the influence of heavymetal contamination on woody plants. Compared withherbs, woody plants have the advantages of large bio-mass and well-developed roots. In the past 12 years, thefeasibility of applying trees to recover the soil pollutedby heavy metals has generated wide public interest(Pulford and Watson 2003).

Table 5 shows that the accumulation of heavy metals bydifferent parts of different tree species varied greatly andthe shrubs were the most typical. The accumulation ofheavy metals by different organs of arbores demonstratedgreat differences. The order of the accumulation of heavymetals by different parts of Ulmus pumila from large tosmall was root, leaf, and branch. The root was the mainpart for the arbores to absorb and accumulate heavymetals, which was consistent with the research results ofWang et al. (2007). For Ailanthus altissima and Robiniapseudoacacia, the order from large to small was leaf, root,and branch. For Periploca sepium Bung, Lespedezabicolor Turcz, and Hippophae rhamnoides, the order wasstem, leaf, and root. The tree species accumulate heavy

metals differently. The ranking of the three species ofarbores accumulating Cd, Cr, and Cu from large to smallamount s was U. pumi la , R. pseudoacacia , andA. altissima, and the order for accumulation of Zn andNi was H. rhamnoides, U. pumila, and A. altissima. Theorder of the three shrubs accumulating five heavy metalsfrom large to small amounts was H. rhamnoides ,P. sepium, and L. bicolor. In addition, Zn was accumulatedin large amounts by the six tree species, whereas Cu wasaccumulated in small amounts.

Different tree species had different abilities to transferheavy metals. In arbores, U. pumila had a strong ability totransfer Ni; R. pseudoacacia had a strong ability to trans-fer Cd and Cr; and A. altissima had a strong transfer abilityof Cd, Zn, Ni, and Cu. In shrubs, P. sepium, L. bicolor, andH. rhamnoides had a strong ability to transfer five heavymetals. Among three arbores, the order of the comprehen-sive abilities to transfer from strong to weak wasA. altissima, R. pseudoacacia, and U. pumila; amongthree shrubs, the order was L. bicolor, P. sepium, andH. rhamnoides. These six tree species had poor ability toaccumulate Cd, Zn, Ni, Cr, and Cu. Among these six treespecies, H. rhamnoides had the largest accumulation co-efficient. Among three arbores, the order of the compre-hensive accumulation ability from strong to weak wasR. pseudoacacia, U. pumila, and A. altissima; amongthree shrubs, the order was H. rhamnoides, L. bicolor,and P. sepium.

Song et al. (2005) successfully introduced the woodynitrogen leguminous plant Leucaena into large tailingbanks. The contents of As, Pb, and Zn were highest in

Table 5 Heavy metal content and transfer and bioaccumulation factors in different woody plants

Type Tree species Organ Cd Cr Cu Ni Zn

Content TF BF Content TF BF Content TF BF Content TF BF Content TF BF

Arbor Ulmuspumila L.

Leaf 0.47 0.83 0.19 3.78 0.53 0.05 4.54 0.8 0.10 7.38 1.06 0.07 23.61 0.93 0.27Branch 0.44 1.89 7.58 1.28 23.18

Root 0.55 5.79 7.60 4.08 25.05

Ailanthusaltissima

Leaf 0.39 1.97 0.13 3.50 0.57 0.07 5.82 1.21 0.08 3.31 1.73 0.03 29.84 1.96 0.37Branch 0.24 2.69 4.08 1.12 32.80

Root 0.16 5.39 5.00 1.28 15.94

Robiniapseudoacacia L.

Leaf 0.49 1.17 0.16 4.70 1.84 0.06 6.44 0.71 0.09 5.79 0.95 0.05 35.76 0.97 0.34Branch 0.28 1.43 3.86 1.87 22.90

Root 0.33 1.67 7.23 3.50 30.22

Shrub Periploca sepiumBung

Shoot 0.52 1.32 0.21 2.16 1.14 0.04 5.53 0.88 0.09 4.07 1.93 0.06 35.20 1.32 0.41Root 0.39 1.89 6.29 2.11 26.73

Lespedeza bicolorTurcz

Shoot 0.80 1.54 0.33 2.79 1.42 0.05 5.73 1.79 0.10 6.23 1.28 0.10 32.70 1.56 0.38Root 0.52 1.97 3.21 4.86 20.90

Hippophaerhamnoides L.

Shoot 0.78 1.59 0.33 1.98 1.19 0.03 6.24 1.16 0.11 5.76 1.03 0.09 40.32 1.05 0.47Root 0.49 1.66 5.38 5.60 38.57

The unit of heavy metal content is mg/kg; the TF and BF have dimensionless unit

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the leaves of Leucaena at 7.82, 15.7, and 124 mg/kg,respectively. In this study, the aboveground part ofA. altissima and R. pseudoacacia had high accumulationof Zn at 32.80 and 40.32 mg/kg, respectively. Comparedwith the investigated tree species, A. altissima andR. pseudoacacia had greater adsorption capacities ofheavy metals. Wang et al. (2011) compared the heavymetals of soil under six types of vegetation on the coalgangue piles and found that the mixed forests of arboresand shrubs demonstrate better absorption of heavy metalsthan the pure forest, which was worthy of use for referenceto the follow-up restoration practice of the research.

Combined with the biomass of the tree species, theaccumulation amount of heavy metals by different woodyplants could be estimated (see Table 6). The biomass ofA. altissima and H. rhamnoides had advantages andexerted a great influence on the accumulation amount ofheavy metals. For single heavy metal pollution,R. pseudoacacia could be used as the heavy-metal-tolerant tree for repairing the soil polluted by Zn, Cd,Ni, or Cu. U. pumila could be planted to repair the soilpolluted by Cd, Ni, Cu, or Cr. A. altissima could beplanted to repair the soil polluted by Cr. H. rhamnoidescould be planted to repair the soil polluted by Zn, Cd, Ni,or Cu. A. altissima could be planted to repair the soilpolluted by Zn or Cr. L. bicolor could be planted to repairthe soil polluted by Cd, Ni, or Cu. To repair the soilpolluted by Cd, Zn, Ni, Cr, and Cu, R. pseudoacacia,U. pumila, and H. rhamnoides could be the first choice.

The order of accumulation for heavy metals by Germanpoplar as an arbor with strong repair potential from largeto small was leaf, root, and branch. Zuo et al. (2009) alsoanalyzed the content of heavy metals in several plants inthe study area and obtained results consistent with thepresent research. Woody plants have low repair efficiencybecause of slow growth. Hence, studies regarding plantsrepairing soil polluted by heavy metals at home andabroad have mostly concentrated on weeds, grass, andother herbaceous plants. However, after the repair by

woody plant biomass, subsequent processing is simplewith light secondary pollution. Therefore, it is still an ef-fective phytoremediation material that can not only repairmining pollution but also bring certain economic benefits.

Conclusions

The damage of heavy metal contamination to the soil andecological environment in the mining area could causehigh levels of ecological danger, in which Cd contamina-tion was the most serious at levels 2–5. However, in thedischarge refuse field, the soil quality improved, the con-tent of heavy metals gradually decreased, and physio-chemical indexes trended toward the normal standard withthe passage of time since dumping. In the areas around thedischarge refuse field, heavy metal contamination was ef-fectively controlled by measures such as planting a forestand building a dam. Heavy metal contamination was verylight in places 250 m away from the discharge refuse field.

Woody plants were sparsely distributed in the coalgangue wastelands, but the biomass was considerable.The content of heavy metals differed in various plants, inwhich the content of Zn was the highest and that of Cd wasthe lowest. The transfer and accumulation abilities ofheavy metals by different plants also varied, in which theaccumulation coefficient of H. rhamnoides was thehighest. R. pseudoacacia, U. pumila, and H. rhamnoidescould be used as pollution-resistant tree species to repairvegetation.

Acknowledgments This research work is partially supported byForestry Industry Research Special Funds for Public Welfare Projects(201104001–4).

Compliance with ethical standards

Conflict of interest There is no conflict of interest regarding publishingthe paper.

Table 6 Heavy metalaccumulation in different woodyplants (mg/kg)

13496 Environ Sci Pollut Res (2016) 23:13489–13497

Type Tree species Spacing (m) Biomass(kg/ha·a)

Accumulation amount of heavy metals(mg/ha·a)

Cd Cr Cu Ni Zn

Arbor Ulmus pumila 2 × 2 435 234 1457 3115 2226 12,025

Ailanthus altissima 2 × 2 514 137 1346 2153 964 13,624

Robinia pseudoacacia 2 × 2 456 176 1398 2348 1746 13,374

Shrub Periploca sepium Bung 1.5 × 1.5 111 58 240 614 452 3907

Lespedeza bicolor Turcz 1.5 × 1.5 108 86 301 619 673 3532

Hippophae rhamnoides 1.5 × 1.5 124 97 246 774 714 5000

The mean value with three replicates is shown

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