Introduction

The term heavy metal (HM) refers to any element whose density is more than 5 (Lozet and Mathieu 1991; Adriano 2001) or 6 g/cm3 (Davies 1987; Thornton 1995). Heavy metals are a group of pollutants that are currently of much environmental concern due to their toxicity to a wide range of organisms. The high concentration of heavy metals in soil is not only caused by natural processes as a result of weathering of rock minerals, but also by anthropogenic activities, such as mining, metal ores smelting, gas exhaust, energy/fuel production, electroplating, industrial emission, and the use of fertilizers and insecticides (Baker 1987; Alloway 1994; Garbisu and Alkorta 2003). In recent decades, the annual global release of heavy metals reached 22,000, 783,000, 939,000, and 1,350,000 t (metric tons) for cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn), respectively (Singh et al. 2003).

In recent decades, interest in ecological threats of heavy metals led to in-depth research on new economical remediation technologies based on plants. Conventional methods employed for remediation of contaminated soils, including chemical, physical, and microbiological methods, are expensive and time-consuming; they can also release secondary wastes and put workers at risk (Wenzel et al. 1999; Lombi et al. 2000; Fitz and Wenzel 2002; Danh et al. 2009). An encouraging and eco-friendly approach is phytoremediation technology wherein plants are utilized to extract, sequester, and/or detoxify contaminants to prevent their dissipation by groundwater or run-off or impede their accumulation via food webs (McGrath et al. 2002; Suresh and Ravishanker 2004; Arthur et al. 2005). It has been reported that phytoremediation is an efficient, non-intrusive, cheap, and esthetically pleasant technology for remediation of contaminated natural environments (Alkorta and Garbisu 2001; Weber et al. 2001; Garbisu et al. 2002).

Plants exhibit three strategies in dealing with high concentrations of heavy metals: exclusion, indication, and accumulation. Excluders are those plants that do not let metal enter their aerial parts and, hence, have a comparatively low metal concentration in the shoot over a wide range of soil metal concentrations by keeping metals in their roots. Indicator plants accumulate metals in their shoots and express some measure of the soil bioavailable metal content. Finally, accumulators translocate and concentrate metals in their aerial parts up to the levels higher than those of the soil (Baker 1981; Raskin et al. 1994; Cunningham 1995).

Over 500 plant species, named hyperaccumulators, concentrate high amounts of trace elements (Reeves and Baker 2000). Hyperaccumulators have been defined as plants that can accumulate more than 10,000 mg/kg of Mn or Zn, 1000 mg/kg of Pb, Ni, Cu, Co, As, or Se, and 100 mg/kg of Cd (Baker and Brooks 1989; Robinson et al. 2006) in their foliage dry matter. Van der Ent et al. (2013) defined hyperaccumulators as plants that can accumulate more than 10,000 mg/kg of Mn, 3000 mg/kg of Zn, 1000 mg/kg of As, Ni, and Pb, 300 mg/kg of Cr, Cu, and Co, and 100 mg/kg of Tl, Cd, and Se in their shoot dry matter. For different elements, the approximate numbers of hyperaccumulator plants are 450 for Ni, 32 for Cu, 30 for Co, 20 for Se, 14 for Pb, 12 for Mn, 12 for Zn, 5 for As, 2 for Cd, and 2 for Tl (Van der Ent et al. 2013). As put forth by some researchers (Arthur et al. 2005), there is a need for better understanding of potential mechanisms in the removal of contaminants from the root zone which is helpful in expanding the application of phytoremediation to clean up other contaminated sites.

Phytoremediation of contaminated soils is achievable by various processes such as rhizofiltration, phytostabilization or phytoimmobilization, phytodegradation, phytotransformation, phytovolatilization, phytostimulation, and phytoextraction (Schwitzguebel 2000; Ali et al. 2013). Among these strategies, phytoextraction (phytoaccumulation), which is a plant’s capability to absorb inorganic (mainly metal) contaminants from soil, is the most prevalent remediation technology (McCutcheon and Schnoor 2003). Phytostabilization is defined as the ability of certain plants to reduce the availability of toxic metals in soil (Gwozdz and Kopyra 2003). Such a process could reduce the danger of the pollutant, but it could not remove toxic metals from the soil (Li et al. 2000).

Phytoremediation efficiency can be measured by calculating bioconcentration factor (BCF) and translocation factor (TF). BCF, defined as the ratio of metal concentration in the roots to that in the soil, could be employed to estimate the efficiency of a plant in absorbing metals from soils (Zhuang et al. 2007; Ladislas et al. 2012; Mahdavian et al. 2017). According to Yoon et al. (2006), plants with BCF and TF greater than 1 have the potential to be used for phytoextraction, while plants with a BCF more than 1 and a TF less than 1 could be useful in phytostabilization. Plants showing TF and BCF values less than 1 are not suitable for phytoextraction (Fitz and Wenzel 2002).

The flora of Iran is made up of about 8000 plant species from 150 families. About 1727 of these species are endemic to Iran (Jalili and Jamzad 1999). Iran has several natural metalliferous (metal-containing soils) and anthropogenic metal-contaminated soils, but not much data is available on their flora and the concentration of trace elements in plants (Ghaderian and Baker 2007). Metal exposure through millennia has driven the evolution of metal resistance in metallophytes (plants that are specifically adapted to and flourish in heavy metal-rich soils) under local environmental conditions (Ernst 2000). Thus, there are possibilities to find locally adapted species in Tang-e Douzan Pb-Zn mine, with beneficial properties for the phytoremediation of metal-polluted soils.

The aims of the present study are as follows: (1) identification of plant species growing on heavily polluted soils at Tang-e Douzan Pb-Zn mine, (2) determination of Pb, Zn, and Cd concentrations in the soils and plants, and (3) evaluation of the usefulness of these plants to remediate metal-contaminated soils.

Materials and methods

Site description

Tang-e Douzan Zn-Pb mining area is located near Fereydoonshahr, 175 km west of Isfahan, central Iran (Fig. 1), in a mountainous area at 2800–2850 m asl, 49° 57′ 7″ E and 33° 2′ 39″ N. Mean annual rainfall is 546.4 mm, about 41% in winter, 31% in autumn, and 24% in the spring. Maximum and minimum temperatures, 34.6 and − 25 °C, in summer and winter, respectively, were recorded at the nearest weather station from January 2010 to September 2016. The main oxide and carbonate minerals in this deposit are hemimorphite, smithsonite, and cerusite; galena, sphalerite, and pyrite are also the main sulfide minerals. In this open mining area, the surface soils naturally include high concentrations of Zn, Pb, and Cd. In this study, soil and plants were collected from four different sites around the mine: the eastern (site 1), western (site 2), southern (site 3), and northern (site 4) sides of the excavated location.

Fig. 1
figure 1

Location of Tang-e Douzan lead-zinc mine

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Plant and soil sampling and analysis

From May 2015 to August 2016, plants growing on four sites of the Tang-e Douzan Pb-Zn mine were collected for identification, metal analysis, and preservation of reference samples. Samples of the soils were taken near plant roots (0–20 cm depth). In order to analyze Pb, Zn, and Cd in soil, samples were air-dried and passed through a < 2-mm sieve. Five grams of each sample was ground, sieved with 80-mesh screen, and oven-dried at 70 °C. Then, a 0.5-g sub-sample was digested with 10 ml of a mixture of 3:1 HCl/HNO3 acids. Tubes were kept at room temperature for a night and then put in a water bath at 80 °C for 2 h. After they were cooled, each digest was filtered through a moisturized Whatman No. 40 filter paper into a 10-ml volumetric flask. Afterwards, flasks were made up to volume with distilled water. Analyses of Pb, Zn, Cd, Mg, and Ca were done using an atomic absorption spectrophotometer (AAS; Shimadzu AA-6200). Exchangeable elements were determined based on the ammonium acetate method (Sparks 1996) by extracting with a 1:4 ratio of soil to extraction solution (1 mol/L NH4OAc, pH 7.0). The suspension was shaken in an end-over-end shaker at 20 °C for 2 h. Next, the soil suspension was left to stand for 5 min and then filtered into a clean test tube. Later on, the filtrate was acidified with HNO3 to 0.2% to analyze the above metals by AAS. To analyze the water-soluble metals, 1:10 proportion of soil and distilled water was mixed and then shaken with a rotary shaker for 24 h. Then, the solution was centrifuged at 3000 rpm and the supernatant was filtered. Finally, AAS was used to measure the concentration of Pb, Zn, Cd, Mg, and Ca in the filtered solution.

The plant samples were washed twice with distilled water. The plant shoots and roots (if present) were separated and oven-dried to constant weight at 70 °C. It should be noted that root sampling was not performed for some species due to a possible threat to the ecosystem. The oven-dried plant materials were ground so that homogenous samples were obtained; subsamples of 0.1 g dry weight were digested in a mixture of HNO3 (65%), HCl (37%), and H2O2 (30%) (6:3:1, v/v/v) and heated at 120 °C for 1 h. After the digests were cooled, they were made up to 10 ml with distilled water. Finally, the solutions were analyzed for Pb, Zn, and Cd (Shimadzu AA-6200). Soil pH was measured by glass electrode using a suspension of soil (10 g) and distilled water (30 ml).

Results

Concentrations of total, exchangeable, and soluble Pb, Zn, Cd, Ca, and Mg, together with the Mg/Ca ratio, in the sampled soils are shown in Table 1. Concentrations of Pb, Zn, Cd, and Ca in these soils are elevated, but Mg and Mg/Ca ratio is low in comparison with ultramafic (serpentine) soils (Reeves and Baker 2000; Reeves 1992). As shown in Table 1, variable total metal concentrations were observed in the soil samples, ranging from 40 to 2500 mg/kg Pb, 8.6 to 1100 mg/kg Zn, 1.9 to 60 mg/kg Cd, 4600 to 43,800 mg/kg Ca, and 890 to 1320 mg/kg Mg.

Table 1 Total (T), exchangeable (E), and water-soluble (S) concentrations of metals in soils of 4 sampling sites
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The exchangeable fraction of elements in the soil ranged from 1.8 to 86 mg/kg Pb, 1.4 to 83 mg/kg Zn, 0.4 to 6.3 mg/kg Cd, 3280 to 4650 mg/kg Ca, and 26 to 49 mg/kg Mg (Table 1). Soluble metal concentrations were 1.6–59 mg/kg for Pb, 0.001–3.7 mg/kg for Zn, 0.22–0.53 mg/kg for Cd, 227–430 mg/kg for Ca, and 1.6–6.4 mg/kg for Mg (Table 1). The Mg/Ca ratio of total metal concentrations was as low as 0.02 to 0.8. The pH of all soils was slightly basic, ranging from 7.85 to 8.33 (Table 1).

In this study, 69 vascular plant species were taken from different sites of the Tang-e Douzan mining area, from 60 genera and 21 families (Table 2). The main represented families were as follows: Asteraceae (16), Brassicaceae (6), Lamiaceae (6), Liliaceae (6), and Poaceae (6). Concentrations of Pb, Zn, and Cd in the shoots of all (and roots of some) the plants are shown in Table 2. Shoot metal concentrations varied from 14 mg/kg in Tanacetum polycephalum to 298 mg/kg in Roemeria hybrida for Pb, 47 mg/kg in Euphorbia cheiradenia to 740 mg/kg in R. hybrida for Zn, and 2 mg/kg in Stachys lavandulifolia to 43 mg/kg in Chenopodium foliosum for Cd.

Table 2 Metal concentrations in roots and shoots of plants and soils
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Assessments of Pb concentration in the roots of some plants, where sampling was possible, were conducted and ranged from 14 to 1030 mg/kg Pb in Tulipa systola and Cerastium dichotomum, 66 to 2040 mg/kg Zn in Allium longivaginatum and Ornithogalum orthophyllum, and 1.8 to 46 mg/kg Cd in Euphorbia condylocarpa and Muscari neglectum, respectively (Table 2).

Discussion

This is the first article on the concentrations of Pb, Zn, and Cd in soils and plant species from the Tang-e Douzan mining area, Isfahan, Iran. According to Kabata-Pendias (2011), the overall mean values of total Pb, Zn, and Cd content of soils are estimated to be 27, 70, and 0.41 mg/kg, respectively. These values for Earth’s crust are 15, 70, and 0.1 mg/kg. The mean values of total soil Pb, Zn, and Cd contents of the 4 sampling sites (Table 1) exceeded these values (184–1480 mg/kg Pb; 395–976 mg/kg Zn, and 4.7–29 mg/kg Cd); therefore, soils of the sampling sites are contaminated by these heavy metals as compared to normal soils. This situation is caused by weathering of parent rocks in Tang-e Douzan mining area. This contamination has led to the lack of vegetation at some locations in the area.

A considerable fraction of total metals in the soil is insoluble and therefore is not instantly bioavailable. However, plants could have direct access to the soluble and exchangeable forms of heavy metals (Lorenz et al. 1997; Pollard et al. 2002).

The amounts of exchangeable Pb and Zn in the soil were limited to 0.3 and 5 mg/kg, respectively; the appraisal of hazard and remediation needs is required over these values (Pruess 1994; Ghaderian et al. 2007). Austrian Standards give the threshold values of 0.03, 1.8, and 0.003 for groundwater Pb, Zn, and Cd concentrations, respectively (BGBl. 504 1991). In the current research, the highest concentrations of exchangeable metals were 86 mg/kg Pb at site 2, 83 mg/kg Zn at site 4, and 6.3 mg/kg Cd at site 1. For soluble fractions, maximum values were 59 mg/kg at site 3, 3.7 mg/kg at site 1, and 0.53 mg/kg at site 3 for Pb, Zn, and Cd, respectively. Thus, large amounts of Pb, Zn, and Cd in the exchangeable and soluble fractions in these sites suggest high soil toxicity. These values show considerable increase in bioavailability of metals, but the toxicity of a specific metal to an organism could not easily be estimated just by the exchangeable or soluble fractions of that element concentration (Otero et al. 2012; Mahdavian et al. 2017). It is important to consider the role of other factors. Differences in the availability and uptake of metal ions may result from their chemical forms, soil pH variations, major element concentrations in soil (e.g., Ca and Mg), and some physical properties, for instance, soil evaporation and porosity together with the local rainfall (Thornton 1999; Van der Ent et al. 2013).

The bioavailabilities of most of the heavy metals in alkaline soils are low in comparison with acidic soils (Wong 2003; Mahdavian et al. 2017). The pH of the sampled soils in the current study was moderately alkaline (Table 1).

Kim et al. (2002) previously showed the protective effects of Ca and Mg on the uptake and toxicity of Pb and Cd in rice (Oryza sativa). They stated that molar ratios of Mg or Ca to Cd or Pb higher than 10:1 were essential for a 50% decrease in uptake of Cd and Pb, as compared to the control treatment. The highest total concentrations of Ca, Mg, Pb, and Cd in soil samples were 43,800, 1320, 2500, and 60 mg/kg, respectively. Maximum values for exchangeable fractions were 4650 for Ca, 49 for Mg, 86 for Pb, and 6.3 for Cd. These amounts are far beyond the 10:1 ratio, particularly in the case of Ca (290 for Ca:Pb, 2071 for Ca:Cd, 5 for Mg:Pb, and 36 for Mg:Cd). Thus, it can be concluded that high concentrations of Mg and especially Ca can reduce the uptake and toxicity of Pb and Cd to plants in Tang-e Douzan area.

Heavy metal uptake from the rhizosphere by plants occurs via passive transport by water mass flow into the roots or an active transport through the plasma membrane of root cells. Some plants may take up elements at a larger concentration than in the surrounding soil and water (Kim et al. 2003). It is expected that the 69 plant species collected from Tang-e Douzan Pb-Zn mine may take up high amounts of metals and show high metal tolerances.

Concentrations of 1 mg/kg Pb, 50 mg/kg Zn, and 0.05 mg/kg Cd are considered as the international standard reference for plants (Van der Ent et al. 2013). In this study, Pb concentrations in plant shoots ranged from 14 to 298 mg/kg with the maximum value in R. hybrida. As a result, no species had a Pb concentration more than 1000 mg/kg in its shoots, which is the notional criterion for hyperaccumulation of Pb (Baker and Brooks 1989; Van der Ent et al. 2013). Additionally, in roots of 10 species (out of 16 analyzed sampled ones), the concentrations of Pb were greater than those of shoots, with TFs ranging from 0.08 to 0.93 in C. dichotomum and A. longivaginatum, respectively (Table 3). This indicates little Pb root to shoot translocation and its immobilization in the roots. On the contrary, T. systola and C. falcata have TFs of 2.85 and 2.79, indicating high Pb root to shoot translocation. Concentrations of Pb in the plants ranged from 14 to 1030 mg/kg in roots, with the highest value in C. dichotomum roots. To date, 14 Pb hyperaccumulators have been reported (Van der Ent et al. 2013); thus, hyperaccumulation of Pb does not occur in most plants grown on Pb-contaminated soils (Reeves 1988; Reeves et al. 2001). Many reports are on the concentrations of Pb in plants which grow on contaminated environments. For instance, root Pb concentrations in the range of non-detectable to 1800 mg/kg were reported by Pitchtel et al. (2000). Furthermore, Stoltz and Greger (2002) showed Pb concentrations in a range of 3.4 to 920 mg/kg in the roots of various plant species growing on mine tailings. Yoon et al. (2006) revealed concentrations of Pb in aerial plant parts from non-detectable to about 500 mg/kg. The range of Pb concentrations between 8 mg/kg in Acantholimon aspadanum and 740 mg/kg in Pinus eldarica was also reported by Ghaderian et al. (2007).

Table 3 Translocation factors (TF), bioconcentration factors (BCF), and extraction factors (EF) for Pb, Zn, and Cd of plants whose roots and shoots were collected
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As an essential micronutrient, Zn in plants is usually found at 10 to 200 mg/kg concentrations (Ghaderian and Ghotbi Ravandi 2012). In the present study, Zn concentrations in the plant shoots and roots had the ranges of 47–740 mg/kg and 66–2040 mg/kg, respectively. Its highest concentrations were found in R. hybrida shoots and of O. orthophyllum roots. Root Zn concentrations were more than those of shoots except for A. longivaginatum, Tragopogon graminifolius, Astragalus sp., and Scorzonera phaeopappa.

There are many reports on Zn concentrations in plants grown in contaminated environments. For example, ranges of 68 to 1630 mg/kg and 17 to 453 mg/kg Zn were reported by Stoltz and Greger (2002) and Yoon et al. (2006), respectively. Both studies’ ranges reported, however, were less than the observed amount in this study. In contrast, Zn concentrations (up to 7600 mg/kg) higher than those observed in the current study were reported by Shu et al. (2002).

Cd is regarded as one of the most eco-toxic metals, having negative effects on all biological processes of humans, animals, and plants. It shows a great potential to adversely affect food quality and the environment (Kabata-Pendias 2011). To date, 2 Cd hyperaccumulators have been reported (Van der Ent et al. 2013). In the current study, Cd concentration in plant shoots was more than the international standard amount for normal plants (0.05 mg/kg) and ranged from 2 to 43 mg/kg with the maximum value in C. foliosum. Thus, none of the plant species accumulated Cd in their shoots more than 100 mg/kg, the notional threshold for Cd hyperaccumulation (Baker and Brooks 1989; Van der Ent et al. 2013).

Cd concentrations in roots of sampled plants were in the range of 1.7 to 46 mg/kg with maximum values in the roots of M. neglectum. Similar studies by Stoltz and Greger (2002) reported Cd concentrations of 0.1 to 12.5 mg/kg. Rio et al. (2002) also reported concentrations of Cd ranging from undetectable to 9.7 mg/kg in analyzed plants. Moreno-Jimenez et al. (2009) showed Cd concentrations from undetectable to 22.04 mg/kg in shoots of plants. All these reports are at a range lower than that found in biomass of plants in this study.

Plants used for phytoremediation to impede the distribution of pollutants via wind, run-off or groundwater (phytostabilization), or to take up and remove contaminants from soil/water environments by accumulating them into shoot biomass (phytoextraction), must have certain characteristics. Plant species which grow fast, yield large biomass amounts, and take up high metal concentrations out of the soil, are encouraging candidates for phytoremediation (Anawar et al. 2006). Moreover, BCF and TF values determine which plants should be selected for phytoremediation purposes (Wu et al. 2011). According to Yoon et al. (2006), plants exhibiting BCF > 1 and a TF < 1 have the capacity to be used for phytostabilization while plants with TF and BCF values > 1 could be useful for phytoextraction. Some authors (Mattina et al. 2003; Ha et al. 2011) defined BCF as the ratio of metal concentration in shoot to that in the soil, whereas others assumed it as root to soil concentration of metal (Yoon et al. 2006; Mahdavian et al. 2017).

In this study, the second definition of BCF was applied and extraction factor (EF) was assumed for shoot to soil metal concentration.

According to Yoon et al. (2006) and Mahdavian et al. (2017):

$$ \mathrm{BCF}={\mathrm{C}}_{\mathrm{root}}/{\mathrm{C}}_{\mathrm{soil}} $$

and

$$ \mathrm{TF}={\mathrm{C}}_{\mathrm{shoot}}/{\mathrm{C}}_{\mathrm{root}} $$

And if we assume

$$ \mathrm{EF}={\mathrm{C}}_{\mathrm{shoot}}/{\mathrm{C}}_{\mathrm{soil}} $$

Regarding

$$ {\mathrm{C}}_{\mathrm{root}}/{{\mathrm{C}}_{\mathrm{soil}}}^{\ast }{\mathrm{C}}_{\mathrm{shoot}}/{\mathrm{C}}_{\mathrm{root}}={\mathrm{C}}_{\mathrm{shoot}}/{\mathrm{C}}_{\mathrm{soil}} $$

So,

$$ \mathrm{EF}={\mathrm{BCF}}^{\ast}\mathrm{TF} $$

where Cshoot and Croot are the concentrations of the metal in the plant shoot and root, respectively, and Csoil is the concentration of the same metal in the soil. Therefore, EF can reflect both BCF (the ability of plant to concentrate metal from soil to its root) and TF (translocation of metal from root to shoot) and can be an appropriate indicator to explain phytoextraction potential of a plant. For example, a plant may have a BCF < 1, but with a very high TF, it can compensate for the shortage of BCF, and hence, the plant can accumulate metal in its shoots in concentrations higher than that in the soil just like a plant with both BCF and TF > 1. Erysimum crassicaule with TF of 2.07 and BCF of 0.53 showed such a situation and had EF of 1.1 for Cd and accumulated it in shoots (7.1 mg/kg) more than soil (6.5 mg/kg) (Tables 2 and 3). O. orthophyllum and R. hybrida subsp. dodecandra showed a similar situation for Cd and Zn with TF < 1 and BCF > 1, but EF > 1 and may show potential for phytoextraction.

According to the data in Tables 3 and 4, plant species that could be suitable for Pb, Zn, and Cd phytostabilization were C. dichotomum for Pb, M. neglectum for all three metals, C. falcata for Zn and Cd, O. orthophyllum for Zn, and R. hybrida subsp. dodecandra for Cd. M. neglectum was the most appropriate sampled plant for phytostabilization of Zn and Cd and O. orthophyllum for Zn.

Table 4 Extraction factors (EF) for Pb, Zn, and Cd of plants whose shoots were collected
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The best choices for phytoextraction of Zn were Bromus squarrosus, Poa bulbosa, and Descurainia sophia. Based on the results, no candidate for phytoextraction of Pb was observed, whereas B. squarrosus, Aegilops columnaris, Allium ampeloprasum subsp. iranicum, A. longivaginatum, Alyssum lanigerum, C. foliosum, Cousinia piptocephala, P. bulbosa, Orobanche aegyptiaca, E. cheiradenia, and D. sophia were the best choice for phytoextraction of Cd.

Bromus squarrosus, with maximum EF of 3.45, is regarded as the most encouraging species for phytoextraction of Zn and Cd contaminated sites. The use of hyperaccumulators has been tested for phytoextraction of heavy metals, which accumulate more metals but produce relatively less aboveground plant biomass. Another way is to use other plants, like the above-mentioned plants, that accumulate less heavy metal concentration but produce more aboveground plant biomass so that the overall metal content is comparable to that of hyperaccumulators (Robinson et al. 1998; Tlustoš et al. 2006).

Conclusions

Plants on Pb, Zn, and Cd contaminated soils of the Tang-e Douzan mine area were collected and identified. Afterwards, the concentrations of these metals in the plants and soil were determined. No single species (out of 69 collected) was identified as a hyperaccumulator. Only the species with both BCFs and TFs > 1, and EFs > 1, have the potential for phytoextraction. Among all the species screened, 4 plants had EF > 1 for Zn and 13 plants for Cd, but no plant showed EF > 1 for Pb. Thus, R. hybrida, B. squarrosus, D. sophia, and P. bulbosa could be the best choices for phytoextraction of Zn and B. squarrosus, A. columnaris, A. ampeloprasum subsp. iranicum, and C. piptocephala for phytoextraction of Cd. In addition, R. hybrida, Ranunculus arvensis, and Fritillaria imperialis with maximum shoot Pb concentrations (298, 247, and 244 mg/kg, respectively) seem to be the best choices for phytoextraction of Pb. Plants with BCF > 1 and TF < 1, including C. dichotomum and M. neglectum for Pb, C. falcata, M. neglectum, O. orthophyllum, and R. arvensis for Zn and C. falcata, M. neglectum, O. orthophyllum, and R. hybrida subsp. dodecandra for Cd, are suggested as the most effective species for phytostabilization of contaminated soils. The tolerance, metal accumulation, and phytoremediation potentials of these plants in controlled experimental condition and/or other contaminated soils with low Ca concentration could be considered as areas for further study.