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Environmental and Experimental Botany
j o u r n a l h o m e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / e n v e x p b o tThe phytoremediation potential for strontium of indigenous plants growing in a
mining area
Ahmet Sasmaz
a,∗, Merve Sasmaz
baDepartment of Geology Engineering, Firat University, 23119 Elazig, Turkey bDepartment of Environmental Engineering, Firat University, 23119 Elazig, Turkey
a r t i c l e i n f o
Article history:Received 29 December 2008 Received in revised form 25 June 2009 Accepted 27 June 2009 Keywords: Enrichment coefficient Phytoremediation Plant Soil Strontium uptake Translocation factor
a b s t r a c t
This study investigated the distribution and accumulation of strontium (Sr) in the shoots and roots of
Euphorbia macroclada (EU), Verbascum cheiranthifolium (VR), and Astragalus gummifer (AS), with respect
to their potential use in phytoremediation. Plant samples and their associated soils were collected from the arid and semi-arid Keban mining area and were analyzed inductively by ICP-MS for Sr. Mean Sr values in the shoots, roots and soil were, respectively, 453, 243 and 398 mg kg−1for E. macroclada; 149, 106
and 398 mg kg−1for V. cheiranthifolium; and 278, 223 and 469 mg kg−1for A. gummifer. The enrichment factors for root (ECR) and shoot (ECS) of these plants were lower than 1 or close to 1, except for the shoot of E. macroclada. The mean translocation factors (TLF) of these plants were higher than 1 and 2.08 for
E. macroclada, 1.47 for V. cheiranthifolium, 1.18 for A. gummifer. It thus appeared that the shoots of these
plants can be an efficient bioaccumulator plant for Sr and it can be used in cleaning or rehabilitating of the contaminated soil and areas by Sr because of their high translocation factors.
Published by Elsevier B.V.
1. Introduction
Soils may be contaminated with zinc and cadmium from antropogenic sources such as sewage sludge or urban composts, fertilizers, emissions from municipal waste incinerators, residues from metalliferous mining, the metal smelting industry, and other human activities. One method for removing heavy metals or other contaminants from soils or water is through the use of green plants, or phytoremediation (Tripathi et al., 2007). This emerging technique offers the benefits of being in situ, low cost, and environ-mentally sustainable (Salt et al., 1998; McGrath et al., 2002).
Phytoremediation involves several approaches and is an improvement over traditional remedies for remediating contam-inated soil, which are costly and usually only treat the upper layers. One approach is phytoextraction, which consists of hav-ing plants take up the contaminants and accumulathav-ing these to extremely elevated levels in the shoots. Plants able to accumulate high concentrations of heavy metals and elements are known as hyperaccumulators. The extreme efficiency of some species in the accumulation of these contaminants also is thought to arise in part from their ability to increase the concentration of metal/metalloids available for uptake from the soil solution within the rhizosphere by root exudation (Ernst, 1998).
∗ Corresponding author. Tel.: +90 424 2370000; fax: +90 424 2411226. E-mail address:asasmaz@firat.edu.tr(A. Sasmaz).
Among the more toxic contaminants, strontium (Sr) is widely found in soils. Strontium (Sr) is a soft, silver-gray metal that occurs in nature as four stable isotopes:84Sr,86Sr,87Sr, and88Sr. Of these, 88Sr is the most prevalent form, comprising about 83% of natural
strontium. The relative abundances of the other three stable iso-topes are84Sr (0.6%),86Sr (9.9%), and87Sr (7.0%). Strontium can
exist in two oxidation states: 0 and +2. Under normal environmen-tal conditions, only the +2 oxidation state is stable. Although natural strontium is not radioactive, strontium can also exist as radioactive isotopes, such as90Sr. This isotope is the most hazardous among the
radioactive isotopes of strontium.90Sr is formed in nuclear
reac-tors or during the explosion of nuclear weapons (ATSDR, 2004) and is a common waste product of nuclear reactors. The acci-dent at the Chernobyl nuclear power plant also introduced a large amount of90Sr into the environment, particularly in the former
Soviet Republics. Risk of cancer increases with increased exposure to90Sr, with risk increasing with the concentration of90Sr in the
environment, and on the exposure conditions (U.S. EPA, 2004). Stable strontium is present in nature chiefly as celestite (SrSO4) and strontianite (SrCO3), and it comprises about 0.0333%
(333 mg kg−1) of the earth’s crust (Wedepohl, 1995). After the strontium is extracted from strontium ore, it is concentrated into strontium carbonate or other chemical forms by a series of chemical processes. Sr compounds, such as strontium carbonate, are used in making ceramics and glass products, in pyrotechnics, in paint pig-ments, in fluorescent lights, in medicines, and in other products (ATSDR, 2004).
0098-8472/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.envexpbot.2009.06.014
Fig. 1. Geological and location map of the study area (simplified fromAkgul, 1987).
The Sr content of soils is highly controlled by parent rocks and climate. Sr is easily mobilized during weathering, especially in oxidizing acid environments and then it is incorporated in clay minerals and strongly fixed by organic matter (Kabata-Pendias and Pendias, 2001). Sr is more strongly adsorbed at higher pH values, but the distribution coefficient values shows less dependence on the soil type. With the possible exception of Sr, there is no evidence for downward movement of radionuclides through the soils during the course of the growing season, although there is some evidence of surface movement of labeled soil particles (Rose et al., 1979).
Soil-to-plant transfer factors have been shown to vary slightly between soil types (Twining et al., 2004). Measurements of soil-to-plant transfer of134Cs,85Sr and65Zn from two tropical red earth
soils (Blain and Tippera) to sorghum and mung crops have been undertaken in the north of Australia. The aim of the study was to identify factors that control bioaccumulation of these radionu-clides in tropical regions, for which few previous data are available. Batch sorption experiments were conducted to determine the dis-tribution coefficient (Kd) of the selected radionuclides at pH values
similar to natural pH values, which ranged from about 5.5 to 6.7 (Twining et al., 2004). The adsorption of Sr was found to be less strong and simpler than that of Cs. There was no evidence of highly selective adsorption on soils or soil constituents and little suggestion of time dependant adsorption or fixation (Cross et al., 2002; Ehlken and Kirchner, 2002; Twining et al., 2004; Wang and Staunton, 2005).
There is also a lack of documented evidence of Sr accumula-tion in aquatic and terrestrial biota (Marinõ et al., 1998) and on the distribution of Sr between different tropic levels of these ecosys-tems (Sadiq et al., 1996). In addition, Sr distribution in plant tissues and organs remains basically uninvestigated. Although Sr is readily transported to the shoots with the xylem sap, in the phloem
trans-port of Sr is greatly restricted (Zeller and Feller, 1998, 2000). Because of this property of Sr, it can be employed as a marker in the studies of xylem transport (Herren, 1997). Sr uptake by roots is appar-ently related to both the mechanism of mass-flow and exchange diffusion. Sr is not very readily transported from roots to shoots; however, the highest concentrations of Sr are often reported at the tops of plants (Kabata-Pendias and Pendias, 2001).Shacklette et al. (1978)reported a toxic Sr level for plants as 30 mg kg−1(ash weight). On the other hand,Kabata-Pendias and Pendias (2001)stated that there is insufficient evidence or study about any deleterious effects on humans or animals of the high levels of stable Sr in the biosphere. Toxic effects of strontium on maize seedling growth were assessed by measuring, in the course of four days of incubation, the daily increments of the primary root length and also the root and shoot length by day 7 of incubation, and the length of the fully elongated cells (Seregin and Kozhevnikova, 2004).
There have been many studies and reports investigating rela-tionships between radioactive90Sr isotope and plants but there are
few documents about stable strontium uptake by different plants. Therefore, the purpose of this study was to determine the enrich-ment and translocation factors between soil and plant parts, with accumulation and distribution of Sr, in the roots and shoots of
Euphorbia macroclada, Verbascum cheiranthifolium Boiss, and Astra-galus gummifer grown in the surface soils of the Keban mining area.
2. Material and methods
2.1. The study area
In this study, the plants and the associated soil samples were collected from an area of the granite–syenites rocks in the Keban mining district of Elazig province in Eastern Turkey (Fig. 1). The
Fig. 2. The distribution of mean Sr concentrations in soils, roots, and leaves of different plants.
plant samples, together with their roots and soils were taken from twenty-one sites (nine Euphorbia, six Verbascum and six Astragalus) of the study area. Since this area has at least 6000 years of min-ing history, the area has been heavily charged with metals by both ancient and modern mining activities.14C absolute age
determina-tions have been confirmed on wooden mining tools discovered in ancient mining cavities bySeeliger et al. (1985). Copper, Zn, Pb, Fe and F ores were mined in this region, but only for short periods.
The plant species in the Keban region can grow under severe climate conditions due to their massive and deep-reaching root sys-tems. These systems give them the ability to live in areas deficient in organic matter. Among the plant species that grow in this area,
Euphorbia macroclada Boiss. (Local name: Sütlegen), Verbascum cheiranthifolium Boiss (Local name: Sigir Kuyrugu) and Astragalus gummifer (Local name: Keven) were examined for Sr content in
this study. These plants were chosen because they are native and dominant species in the study area.
2.2. Preparation of samples
2.2.1. Soil samples
The soils in the study area were Aridosol, with a loamy clay tex-ture (35.6% sand, 42.3% silt and 22.1% clay), between pH 7.2 and 7.8 and with an organic matter content of 0.88–1.34%. An X-ray diffraction study on the clay minerals was not performed. The soil samples (about 500) were also collected at a depth of 30–40 cm and surrounding the roots of the plant. After drying in an oven at 100◦C for 4 h and removing rocks, the soil samples were ground using hand mortars. For digestion of the soil samples, a mixture of HCl–HNO3–H2O (6 ml of the mixture of 1/1/1 was used per 1.0 g)
was used for one hour at 95◦C. This treatment dissolved all soil samples except for silicates, and the digests were analyzed using ICP/AES and MS techniques for strontium at the ACME Analytical Labs, Vancouver, Canada (www.acmelab.com).
2.2.2. Plant samples
The plant samples were randomly collected from the sites determined in accordance with a pattern representing the whole characteristics of the Keban mining area. Three samples of the shoots and roots were taken from each sampling site. The root
sam-ples were taken at a depth of 30–40 cm below the surface. The shoot and root samples of the studied plants were thoroughly washed with tap water, followed by distilled water and dried at 100◦C in an oven for thirty minutes and then at 60◦C for twenty-four hours. The chelating EDTA wash was applied, and no difference was observed between EDTA washing and without EDTA washing. The dried plant samples (approximately 2.0–3.0 g) were ashed by heating at 250◦C, and then the temperature was gradually increased to 500◦C for two hours. The ashed samples were digested in HNO3for one hour, and
then digestion of the ashed samples was realized in a mixture of HCl–HNO3–H2O for one hour (6 ml of the mixture of 1/1/1 was used
for 1.0 g of the ashed sample) at 95◦C. The digests were analyzed using ICP/AES and MS techniques for strontium as for soils.
2.3. Enrichment coefficients of roots (ECR)
Enrichment coefficients were found by calculating the ratios of specific activities in plant roots and soils (concentration in mg kg−1 of plant root divided by concentration in mg kg−1of soil). This value is used as an index for the accumulation of trace elements in plant parts or for the transfer of elements from soil to plant root (Chen et al., 2005).
2.4. Enrichment coefficient for shoots (ECS)
Enrichment coefficients for shoots (ECS) were very important factors (concentration in mg kg−1 of plant shoot divided by con-centration in mg kg−1 of plant root), as they indicate the degree of phytoremediation of a given species (Zhao et al., 2003) and this value is used as an index for the transfer of elements from soil to plant shoot. This represents a special ability of the plant to absorb and transport metals from sediment and then to store them in their above-ground parts (Baker, 1981; Brown et al., 1994; Wei et al., 2002).
2.5. Translocation factors
Translocation factors (TLF) are obtained by calculating the ratio of metal in plant shoot to that in the plant roots (concentration in mg kg−1of plant shoot divided by concentration in mg kg−1of
Plant name Sample No Desc. of sample Sr in soil Sr in root Sr in shoot ECR ECS TLF
E. macroclada, EU-21 Sandy 160± 18 213± 12 477± 58 1.33 2.98 2.84
EU-24 Silt, clay 717± 56 239± 36 378± 53 0.33 0.53 1.58
EU-26 Clay, sandy 455± 36 251± 18 336± 44 0.55 0.74 1.34
EU-29 Mining, silt 514± 69 183± 22 479± 48 0.36 0.93 2.61
EU-31 Mining, clay 483± 33 171± 21 531± 88 0.35 1.1 3.1
EU-34 Sandy 156± 23 150± 11 272± 47 0.96 1.74 1.82
EU-41 Clay, sandy 469± 37 504± 63 619± 49 1.07 1.32 1.23
EU-44 Sandy, mining 325± 49 292± 12 571± 53 0.9 1.76 1.96
EU-45 Clay, mining 303± 47 185± 16 412± 29 0.61 1.36 2.23
Mean 398 243 453 0.72 1.38 2.08
V. cheiranthifolium VR-18 Clay, silt 442± 76 80± 5 228± 43 0.18 0.52 2.85
VR-25 Silt, rock 612± 84 126± 18 219± 36 0.21 0.36 1.74 VR-25 Y Silt, rock 612± 28 111± 6 98± 14 0.18 0.16 0.88 VR-27 Sandy, silt 150± 22 116± 14 150± 22 0.77 1.00 1.29 VR-35 Sandy 156± 9 52± 12 58± 8 0.33 0.37 1.1 VR-47 Clay, silt 413± 23 149± 19 141± 16 0.36 0.34 0.95 Mean 398 106 149 0.34 0.46 1.47
A. gummifer AS-22 Sandy, mining 498± 66 178± 56 172± 10 0.35 0.35 0.97
AS-28 Sandy 112± 24 213± 32 328± 29 1.75 2.69 1.54
AS-32 Clay, mining 580± 77 252± 16 259± 51 0.43 0.45 1.03
AS-36 Silt, mining 378± 54 195± 26 204± 18 0.52 0.54 1.05
AS-40 Silt, clay 705± 93 198± 22 246± 21 0.28 0.35 0.97
AS-42 Clay, silt 531± 56 301± 33 456± 25 0.57 0.86 1.51
Mean 496 223 278 0.65 0.87 1.18
root). In metal accumulator species, a translocation factor greater than 1 is common, whereas in metal excluder species, translocation factors are typically lower than 1 (Zu et al., 2005).
3. Results and discussion
3.1. Sr concentrations in soils
Sr contents of the soil samples in the study area were found out to be between 112± 24 and 717 ± 56 mg kg−1(mean: 418 mg kg−1)
(Fig. 2; Table 1). Among twenty-one soil samples, Sr concentra-tions were observed to be higher than in previous reports (average 150 mg kg−1) in different surface soils (Loess and silty soils, U.S.; Loamy and clay soils, New Zeland; Podzols and sandy soils, Aus-tralia; Various soils, Canada; Forest soils, U.S.;Pais and Jones, 2000; Kabata-Pendias and Pendias, 2001), except for one sample. Sr con-centrations of soils in EU-24 (where EU refers to a Euphorbia sample) and AS-40 (AS refers to an Astragalus sample) samples had the high-est Sr concentrations (717± 56, 705 ± 93 mg kg−1, respectively) in
the soils of the study area (Fig. 2;Table 1) and consist of silt and clay minerals.
The Keban region is widely covered by intermediate rocks (syen-ite, diorite) and different metamorphic rocks. Due to weathering of felsic magmatic rocks, the Sr contents of studied soils were very high compared with those of previously studies rocks and soils (Pais and Jones, 2000; Kabata-Pendias and Pendias, 2001). In our study, Sr showed positive linear correlations with Ca (r = 0.82), K (r = 0.49) and B (r = 0.58), but it did not show any correlations with other heavy metals in the studied soils (Table 2). Thus, these correlations in the study area show that Sr was transferred to the mining area together with magmatic phases in a different pattern from those of other metals, including Cu, Pb, Zn, Fe, As, Cd (Sagiroglu et al., 2006), Cr, Ni, Co (Sasmaz and Yaman, 2006), Tl (Sasmaz et al., 2007), B (Sasmaz, 2008) and Se (Sasmaz, 2009). The reason for this is that the source of Sr in the study area is connected with magmatic pro-cesses, while that for the other metals, such as Cu, Pb, Zn, Fe, As, Cd, Cr, Ni, Co, Tl and Se were hydrothermal. Besides, it is observed to not affect of Sr variability with soil properties such as pH, organic matter and texture, by virtue of these properties among samples are to close each others.
3.2. Sr concentrations in plants
3.2.1. Euphorbia macroclada Boiss (EU)
Sr concentrations in the shoot, roots, and the rhizosphere soil of E. macroclada are presented inFig. 2andTable 1. Mean Sr val-ues in the shoot, roots and soil for Euphorbia were 453, 243, and 398 mg kg−1, respectively. As indicated, Sr values in the rhizosphere soil around Euphorbia plants were significantly lower than the mean Sr values in the shoot, but Sr values in soils were higher than Sr concentrations in the root of E. macroclada, except for two sam-ples. The Sr values of all E. macroclada varied between 150± 11 and 504± 63 mg kg−1 for the root, and 272± 47 and 619 ± 49 mg kg−1
for the shoot on a dry weight basis. As shown inFig. 2, Sr values in the shoots of all Euphorbia samples were always higher than the Sr values of their roots. These Sr concentrations in the plant parts were also higher than the normal Sr concentrations reported in plants from European forest ecosystems of Russia and Germany (Markert and Vtorova, 1995) and in food and feed plants (details in Table 62 ofKabata-Pendias and Pendias, 2001). Enrichment coef-ficients are very important factors when considering the potential for phytoremediation by a given species (Zhao et al., 2003). The Sr concentrations in roots are invariably greater than that in soil, enrichment coefficients are >1. This indicates a special ability of the plant to absorb and transport metals from soils and to store these in their above-ground parts (Baker, 1981; Wei et al., 2002). The enrich-ment coefficients (ECR) of the E. macroclada roots for Sr are shown inFig. 3andTable 1, with the mean enrichment coefficient of 0.72. However, the enrichment coefficients of two of nine root samples were higher than 1 and the values of two samples were very close to 1. In this study, the enrichment coefficients (ECS) for Sr in the shoot of E. macroclada were higher than 1.0, except for three sam-ples (Fig. 3), with an average ECS of 1.38 and this was also higher than 1. On the other hand, the mean translocation factor (TLF) for
E. macroclada for Sr was 2.08 (Fig. 3andTable 1) and all translo-cation factor values of E. macroclada were always higher than 1. In metal accumulator species, the enrichment coefficient for shoots and translocation factors greater than 1 are common, whereas the translocation factors and the enrichment coefficients for shoots are typically lower than 1 in metal excluder species (Zu et al., 2005). Translocation factors higher than 1 indicate a very efficient ability
Table 2
The correlations among the metals in the studied soils.
Mo Cu Pb Zn Ag Ni Co Mn Fe As Au Cd Sb Bi Cr Ba B Sr Ca K Mo 1.00 Cu 0.89 1.00 Pb 0.97 0.86 1.00 Zn 0.89 1.00 0.87 1.00 Ag 0.96 0.87 0.95 0.87 1.00 Ni −0.05 −0.07 0.08 −0.08 0.01 1.00 Co 0.88 0.95 0.87 0.94 0.86 0.20 1.00 Mn 0.40 0.23 0.52 0.25 0.29 0.13 0.28 1.00 Fe 0.91 0.91 0.90 0.91 0.91 0.19 0.97 0.28 1.00 As 0.84 0.95 0.80 0.95 0.80 −0.06 0.94 0.25 0.89 1.00 Au 0.88 0.93 0.87 0.93 0.85 −0.02 0.90 0.32 0.87 0.88 1.00 Cd 0.90 1.00 0.87 1.00 0.88 −0.06 0.95 0.22 0.91 0.96 0.93 1.00 Sb 0.23 0.12 0.36 0.15 0.13 0.10 0.15 0.85 0.11 0.19 0.30 0.13 1.00 Bi 0.96 0.85 0.97 0.86 0.98 0.08 0.87 0.37 0.93 0.78 0.84 0.86 0.18 1.00 Cr 0.19 0.10 0.25 0.10 0.19 0.74 0.39 0.15 0.40 0.22 0.20 0.11 0.18 0.24 1.00 Ba 0.61 0.60 0.69 0.62 0.54 −0.08 0.55 0.74 0.49 0.58 0.69 0.60 0.77 0.57 0.01 1.00 B 0.40 0.19 0.39 0.18 0.29 0.35 0.30 0.23 0.30 0.20 0.20 0.20 0.14 0.30 0.50 0.12 1.00 Sr 0.22 0.13 0.21 0.12 0.11 0.29 0.28 0.20 0.29 0.25 0.18 0.14 0.20 0.13 0.69 0.07 0.58 1.00 Ca 0.08 −0.03 0.15 −0.03 −0.03 0.49 0.16 0.48 0.13 0.10 0.13 −0.02 0.57 0.02 0.73 0.31 0.49 0.82 1.00 K 0.76 0.60 0.81 0.62 0.67 0.12 0.69 0.74 0.71 0.67 0.67 0.61 0.64 0.72 0.49 0.74 0.41 0.49 0.55 1.00
Fig. 3. Translocation factors (TLF), and the enrichment coefficients for root (ECR) and shoot (ECS) of different plants.
to transport metal from roots to leaves, most likely due to effi-cient metal transporter systems (Zhao et al., 2002), and probably sequestration of metals in leaf vacuoles and the apoplast (Lasat et al., 2000). Some metals, such as Zn and B, have the highest transfer coefficients which are a reflection of their relatively poor sorption in the soils. In contrast, certain metals, such as Cu, Co, Cr, and Pb, have low coefficients because these metals are usually strongly bound to sediment colloids (Moore and Romanorty, 1984).
3.2.2. Verbascum cheiranthifolium Boiss (VR)
Sr concentrations in the shoot, roots and the rhizosphere soil of Verbascum cheiranthifolium Boiss plant are shown inFig. 2and Table 1. The mean Sr values in the soil, roots and shoots were 398, 106 and 149 mg kg−1, respectively. Moreover, the Sr values of the soil where V. cheiranthifolium plant grows were observed to be sig-nificantly higher than the mean Sr values in the shoot and the root. The Sr values of all V. cheiranthifolium varied between 52± 12 and 149± 19 mg kg−1for the root, and 58± 8 and 228 ± 43 mg kg−1for
the shoot, on a dry weight basis. As shown inFig. 2, Sr values in the shoots of all V. cheiranthifolium samples were higher than Sr values of their roots, except for two samples. The enrichment coef-ficients (ECR) of V. cheiranthifolium root for strontium are shown in Fig. 3andTable 1, with a mean values of 0.34, which was lower than 1. The mean translocation factor (TLF) for Sr in V. cheiranthifolium was 1.47 (Fig. 3andTable 1) and all translocation factors for all V.
cheiranthifolium plants were higher than 1, except for two samples.
3.2.3. Astragalus gummifer (AS)
Sr concentrations in the soil, roots and shoots of A. gummifer are presented in Fig. 2 and Table 1. The mean Sr values in the soil, roots and shoots were 469, 223 and 278 mg kg−1, respectively. The Sr values of the soil where A. gummifer plant grows were sig-nificantly higher than the mean Sr values in the shoot and the root of A. gummifer. The Sr values of all A. gummifer plants varied between 178± 56 and 301 ± 33 mg kg−1for the root, 172± 10 and
The enrichment coefficients (ECR) in the root of A. gummifer for Sr are shown inFig. 3, with a mean value of 0.65. The translocation factors (TLFs) for Sr in A. gummifer varied between 0.97 and 1.54 (Fig. 3andTable 1) and all translocation factor values of A. gummifer were higher than 1, except for two samples.
For a plant to be considered a hyperaccumulator, the plant should typically contain, at least, a few times more of a metal (or element) than occurs in plants from non-polluted environments or other plants grown in the same soil (Zu et al., 2005). InFig. 2, it is apparently seen that the shoot of E. macroclada, V. cheiranthifolium and A. gummifer samples have a few times higher Sr than that in the soil samples of the studied area (Table 1).
4. Conclusions
The mean Sr concentration of the soils in the study area was 418 mg kg−1which is higher than mean Sr concentrations in soils reported previously for different countries. The Sr contents of the roots and the shoots of all studied plants were lower than the mean Sr concentrations in their soils, except for the shoot of Euphorbia. The mean Sr value of Euphorbia shoot was higher than both mean Sr values of its roots and its soil. The mean ECR, ECS and TLF of E.
macroclada were 0.72, 1.38 and 2.08, respectively, and these results
indicate that E. macroclada could prove useful both as biogeochem-ical indicator of Sr and as a biomonitor for environmental pollution in arid-semi arid environment, by virtue of its high ECS and TLF. V.
cheiranthifolium has a low ECR and ECS, but its TLF is only slightly
higher than 1. V. cheiranthifolium has low uptake capacity to root and shoot from soil for Sr and is probably not useful for phytoreme-diation purposes. In contrast, the ECR and ECS of A. gummifer are lower than 1, but close to 1, and its TLF is higher than 1. For this reason, A. gummifer can be useful either for the cleaning of Sr from contaminated soils or for phytoremediation.
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