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EDTA-EnhancedPhytoremediation of Lead-Contaminated Soil by CornAnna Hovsepyan a & Sigurdur Greipsson aa Department of Biological and EnvironmentalSciences , Troy University , Troy, AL, USAPublished online: 14 Feb 2007.

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Journal of Plant Nutrition, 28: 2037–2048, 2005

Copyright © Taylor & Francis Inc.

ISSN: 0190-4167 print / 1532-4087 online

DOI: 10.1080/01904160500311151

EDTA-Enhanced Phytoremediationof Lead-Contaminated Soil by Corn

Anna Hovsepyan and Sigurdur Greipsson

Department of Biological and Environmental Sciences, Troy University,Troy, AL, USA

ABSTRACT

EDTA-enhanced phytoremediation by corn (Zea mays L.) of soil supplemented with500 mg L−1 lead (Pb) was examined. The chelate EDTA was used in order to increasePb bioavailability at four levels: 0 (control), 0.5 (low), 1.0 (medium), and 2.5 mmolkg−1 (high). Plants were grown under controlled conditions in a growth-chamber withsupplementary light. An EDTA concentration of 5.0 mmol kg−1 was lethal to plants. Athigh and medium EDTA levels plants grew significantly less than control ones. Leadconcentrations in corn leaves increased with increased EDTA levels. Plants subjected tomedium EDTA level had the greatest root to shoot Pb translocation. Plants subjected tohigh EDTA level showed high phosphorus (P) uptake and translocation within plants.Therefore, possibly it was not only Pb that caused toxic effect on plants, but also thehigh internal concentration of P that in turn could have complexed active Fe.

Keywords: EDTA, lead contamination, heavy metals, phytoextraction, phytoremedia-tion, Zea mays

INTRODUCTION

Anthropogenic pollution of soils by heavy metals is a major environmental con-cern (Ripley et al., 1996). Lead (Pb) is one of the most widespread heavy metalpollutants in soils (Huang et al., 1997; Lambert et al., 1997). Soil contamina-tion has been associated with Pb smelters (Anderson et al., 2000; Gibson et al.,2002; Judah, 2004). Lead is persistent in soils since it has low solubility andbioavailability (Epstein et al., 1999) as a result of complexation with organic

Received 4 February 2004; accepted 27 July 2005.Address correspondence to Sigurdur Greipsson, Department of Biological and Envi-

ronmental Sciences, Troy University, Troy, AL 36082, USA. E-mail: greipsso@troy.edu

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and inorganic compounds (Greman et al., 2001; McGrath et al., 2001). Lead ispotentially harmful to living organisms including humans, and it has no knownbiological role in soils (Lambert et al., 1997).

Phytoextraction is an efficient, cost-effective method for in-situ treatmentof contaminated soils (Salt et al., 1995). This method uses plants to clean uppolluted soils (Huang and Cunningham, 1995) and is considered safe for humansand the environment (Weatherford et al., 1997). Phytoextraction has been usedsuccessfully to clean up Pb-contaminated soil (Huang et al., 1997; Chaudhryet al., 1998).

True Pb-hyperaccumulators have not yet been identified (Kos and Lestan,2003). Corn (Zea mays L.) has a great potential to be used in Pb-phytoextractionsince corn seeds are readily available, and cultivation of the species as well asnutritional requirements are well established (Ripley et al., 1996; Huang et al.,1997; Weatherford et al., 1997). In addition, corn grows rapidly, produces largebiomass, and can be grown in most ecoregions of the United States (Ripleyet al., 1996).

Heavy metals are maintained in soil primarily by adsorption onto the sur-faces of clay particles, complexation by organic matter in soil, and precipitationreactions (Foy et al., 1978; Lange et al., 1983; Walton et al., 1994). Hence, only asmall portion of heavy metals in soil is bioavailable (Khan et al., 2000; Chaudhryet al., 1998). Addition of chelating agents increases heavy metal bioavailabilityand solubility in soil and subsequently enhances heavy metal uptake by a plant(Stanhope et al., 2000). Supplementing soil with a synthetic chelating agent suchas ethylene diamine tetraacetic acid (EDTA) is an efficient method to enhanceheavy metal uptake by plants (Dekock and Mitchell, 1957; Huang et al., 1997;Khan et al., 2000; Stanhope et al., 2000; Greman et al., 2001). Addition of EDTAto soil induces translocation of Pb within plants (Blaylock et al., 1997; Huanget al., 1997; Gleba et al., 1999; Cooper et al., 1999; Epstein et al., 1999; Deramet al., 2000). The EDTA is stable in soil and forms Pb-EDTA complex, whichis highly water-soluble and is therefore available to plants (Epstein et al., 1999;Hong et al., 1999; Greman et al., 2001). Studies suggest that metal solubilityand bioavailability may be increased by addition of EDTA in the range of 0.1 to10.0 mmol EDTA kg−1 soil (Stanhope et al., 2000; Greman et al., 2001). How-ever, optimal concentration may vary between soil types and plant species. Theaims of this study were to determine sublethal doses of EDTA and investigatethe effect of EDTA on Pb uptake by corn grown in soil supplemented with Pb.

MATERIALS AND METHODS

Soil Description

The soil used in this study was collected from New Brockton, Coffee County,AL, USA (31◦26.293′ N, 85◦54.275′ W). The soil is classified as Ultisol and

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EDTA of Lead-Contaminated Soil by Corn 2039

it belongs to the Red-Bay series (Childs, 1979). The soil texture is defined asloamy sand with low organic matter. The soil is considered to be low in naturalfertility with pH 4.5 to 6.0 (Childs, 1979). Soil was analyzed for Pb and selectedmacronutrients [phosphorus (P), potassium (K), calcium (Ca), and magnesium(Mg)] and micronutrients [iron (Fe), zinc (Zn), copper (Cu), and manganese(Mn)]. Soil analysis was performed using an Inductively Coupled Argon PlasmaSpectrometer (ICAP) at the Soil Testing Laboratory, Department of Agronomyand Soils, Auburn University, AL.

Seed Germination and Growth Conditions

Seeds of corn (Zea mays) were imbibed in water for one day and subsequentlygerminated for 7–8 days on a moist double-layered filter paper (Whatman no. 1)in Petri dishes. Three kilograms of soil were added to individual pots (4 L). Threeseedlings of similar size were planted in each pot and thinned to one per potafter ten days. Plants were grown in a growth-chamber at Troy University, ina completely randomized design with a 16 h photoperiod supplemented withcool-white fluorescent lamps (5850 Lux) at 20–27◦C and relative humidity of47–65%. Plants were watered regularly with deionized water (150 mL). Thelength of the longest leaf was measured every ten days.

Determination of Sublethal Levels of EDTA on Corn

The following levels of EDTA were examined: 0 (control), 0.1, 0.5, 1.0, 2.5,and 5.0 mmol kg−1. The EDTA (150 mL) application commenced two weeksafter seedlings were planted. After five weeks of growth plants were harvested.

Effect of EDTA on Lead Uptake of Corn Exposedto Lead-Contaminated Soil

Soil was supplemented with 500 mg L−1 Pb in order to challenge plants. Anaqueous solution (150 mL) of lead nitrate Pb(NO3)2 at 500 mg L−1 Pb wasadded seven times at equal intervals. The EDTA application commenced withfour weeks after seedlings were transplanted into the pots. The EDTA wasadded to treatments at the following concentrations: 0 (control), 0.5 (low), 1.0(medium), and 2.5 mmol kg−1 (high). Plants were harvested after eight weeksof growth. Plant shoots and roots were separated and washed with tap waterand then rinsed in deionized water and consequently dried in an oven at 68◦Cto a constant weight. Dried plant material was stored in paper envelopes in acool dark place to await chemical analysis.

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Chemical Analysis

The roots and the leaf tips of plant shoots were digested according to the dry ash-ing digestion procedure (Miller, 1998). Prior to the chemical digestion, plantswere dried again in an oven at 68◦C for 24 hours. Plant material was ground topass a 40-mesh stainless steel sieve. All glassware used in the digestion processhad been cleaned in boiling nitric acid solution for an hour to eliminate possiblesample contamination. Weighed plant samples (0.5 g) were placed into clean50 mL beakers and put in a muffler furnace at 450◦C. This temperature wasmaintained for about four hours until all carbon was burned off. Ten mL of1 N HNO3 were added to the samples and evaporated to dryness on a hot plateand then, 10 mL of 1 N HCl were added to dissolve the residue. The digestwas consequently brought to 100 mL and filtered (Whatman no. 1) into samplebottles. Samples were analyzed for selected macronutrients and micronutrientsusing ICAP (detection limit greater than 0.5 mg kg−1).

Statistical Analysis

Statistical analysis of the data was performed using the SPSS (vs. 11.0) statis-tical package. Data on metal concentration in leaves and roots was analyzedusing one-way analysis of variance (ANOVA) followed by the LSD (LeastSignificant Difference) multiple range tests. Data was square root transformedwhere needed to adhere to the assumption of normality and to stabilize variance.Statistical significance was accepted at a level of p ≤ 0.05.

RESULTS

Soil Analysis

The soil had relatively low levels of Pb (0.2 mg kg−1) and Zn (0.4 mg kg−1).Concentrations of other metals were also low: Fe (6.3 mg kg−1), Mg (23.8 mgkg−1), and Mn (10.4 mg kg−1). Concentrations of macronutrients were alsolow: P (14.5 mg kg−1), K (18.1 mg kg−1), and Ca (122.2 mg kg−1).

Determination of Sublethal Levels of EDTA

The EDTA concentration of 5.0 mmol kg−1 was lethal to all plants. Subjectingplants to sublethal levels of EDTA affected growth of plants. Control plantsgrew (indicated by the length of the longest leaf) significantly better thanplants subjected to 2.5 (p = 0.03), and 5.0 mmol kg−1 (p = 0.03) EDTA levels(Figure 1). Furthermore, plants exposed to 0.1 mmol kg−1 EDTA level grew

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EDTA of Lead-Contaminated Soil by Corn 2041

Figure 1. Determination of sublethal levels of EDTA on Z . mays. Six EDTA concen-trations were tested: 0 (control), 0.1, 0.5, 1.0, 2.5, and 5.0 mmol kg−1. Different lettersindicate a significant difference (p ≤ 0.05).

significantly better than plants subjected to 5.0 mmol kg−1 EDTA level (p =0.05) (Figure 1).

Effect of EDTA on Growth of Plants Subjectedto Lead-Contaminated Soil

Control plants grew significantly better than plants exposed to high (2.5 mmolkg−1) (p = 0.02) EDTA level (Figure 2). Plants subjected to high EDTA levelshowed toxic effects manifested as necrosis and chlorosis. Plants exposed tolow (0.5 mmol kg−1) and medium (1.0 mmol kg−1) EDTA levels grew less thancontrol, although significant differences were not established (Figure 2).

Figure 2. Effects of 0.5, 1.0, and 2.5 mmol kg−1 EDTA concentrations on growth ofZ . mays exposed to soil supplemented with 500 mg L−1 of Pb. A star indicates asignificant difference (p ≤ 0.05).

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Figure 3. Lead concentrations in roots and leaves of plants treated with 500 mg L−1

of Pb. Concentrations of EDTA tested: control (0 mmol kg−1), low (0.5 mmol kg−1),medium (1 mmol kg−1), and high (2.5 mmol kg−1). The values are averages of three repli-cates. Error bars are standard errors of the mean. Different letters indicate a significantdifference (p ≤ 0.05).

Effect of EDTA on Lead Concentrations in Plants

Lead concentrations in leaves increased with increased EDTA levels (p = 0.05)(Figure 3). The highest Pb concentrations in leaves (310 mg kg−1) were foundin plants treated with high EDTA level, but this value was not significantlydifferent from plants exposed to medium EDTA (Figure 3). Control plants hadsignificantly lower Pb concentrations than plants at low (p = 0,004), medium(p = 0.001), and high (p = 0.001) EDTA levels.

Concentrations of Pb in the roots ranged from 414 to 1120 mg kg−1. Leadconcentrations were much higher in roots than in leaves at high (p = 0.006),medium (p = 0.03), low (p = 0.05), and zero (p = 0.01) EDTA levels (control);indicating low translocation of Pb within plants (Figure 3).

Effect of EDTA on Macronutrients in Plants

Plants treated with high EDTA had the highest concentrations of P in leaves(9895 mg kg−1) (Figure 4). Phosphorus concentrations in roots of plants treatedwith high EDTA were significantly higher than P concentrations in control(p = 0.007) and plants treated with low (p = 0.003) and medium (p = 0.010)EDTA levels.

Potassium concentrations were significantly higher in leaves of plantstreated with high EDTA than those of plants treated with low EDTA level

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Figure 4. Phosphorus concentrations in roots and leaves of plants treated with500 mg L−1 of Pb. Concentrations of EDTA tested: control (0 mmol kg−1), low (0.5 mmolkg−1), medium (1 mmol kg−1), and high (2.5 mmol kg−1). The values are averages ofthree replicates. Error bars are standard errors of the mean. Different letters indicate asignificant difference (p ≤ 0.05).

(p = 0.01) (Figure 5). Potassium concentrations were low in roots and did notdiffer significantly among treatments (Figure 5).

Effect of EDTA on Micronutrients in Plants

The highest Mn concentrations in roots were found in plants treated with highEDTA; these values were significantly higher than those of control plants

Figure 5. Potassium concentrations in roots and leaves of plants treated with 500 mgL−1 of Pb. Concentrations of EDTA tested: control (0 mmol kg−1), low (0.5 mmolkg−1), medium (1 mmol kg−1), and high (2.5 mmol kg−1). The values are averages ofthree replicates. Error bars are standard errors of the mean. Different letters indicate asignificant difference (p ≤ 0.05).

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Figure 6. Manganese concentrations in roots and leaves of plants treated with500 mg L−1 of Pb. Concentrations of EDTA tested: control (0 mmol kg−1), low (0.5 mmolkg−1), medium (1 mmol kg−1), and high (2.5 mmol kg−1). The values are averages ofthree replicates. Error bars are standard errors of the mean. Different letters indicate asignificant difference (p ≤ 0.05).

(p = 0.03) (Figure 6). Manganese concentrations in leaves were not signifi-cantly different among treatments (Figure 6).

Concentrations of Fe and other heavy metals such as Zn and Cu in plantleaves and roots were not significantly different among treatments (data notshown). Concentrations of Mn, Fe, Zn, and Cu were significantly higher in rootsthan in leaves; indicating low translocation of these elements within plants.

DISCUSSION

The importance of this work is the manifestation of Pb toxicity brought bythe high concentrations of P in plants subjected to high level of EDTA. Theresults showed that Pb concentrations were much higher in plant roots than inleaves indicating low translocation of Pb within plants. This low translocationof Pb within plants appears to be a limiting factor for phytoremediation ofpolluted soils. A key factor for low translocation of Pb in plants could beinternal concentrations of P. Phosphorus concentrations within plants couldhave profound influence on the amount of active Fe in plants and therefore theability of plants to tolerate heavy metals (Greipsson, 1992, 1995). The EDTAaids in the mobility of P in the soil and eventual uptake of P by plants (Kirkham,2000). The results suggested that plants subjected to high EDTA levels had highP translocation within plants. Previous studies have suggested that Fe interfereswith the absorption and assimilation of P by forming iron phosphates (Luoet al., 1997). High internal P concentrations could therefore have contributed totoxicity effects in plants that resemble heavy metal toxicity (Foy et al., 1978).

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Hence, possibly it were not only the high concentrations of Pb in the leaves thatcaused the toxic effects on plants subjected to high levels of EDTA but morelikely the high internal concentration of P, which indirectly contributed to thetoxic effect by complexing the internal active Fe. Iron concentrations remainedsimilar in leaves among treatments. The results demonstrate the importance ofthe ratios of Pb, Fe, and P concentrations within plants in determining heavymetal toxicity.

Previous studies have suggested that addition of EDTA to soil enhancestranslocation of Pb within plants (Huang et al., 1997; Gleba et al., 1999; Deramet al., 2000). The results showed that Pb concentrations in leaves increasedstepwise with increased EDTA levels. However, significant differences in Pbconcentrations in leaves were not found between plants exposed to medium andhigh EDTA levels. The results showed that in general, translocation of Pb withinplants exposed to EDTA was significantly higher than translocation of Pb withincontrol plants. Moreover, heavy metal toxicity effect on plants increased withincreasing EDTA levels. High EDTA level significantly reduced the growth ofplants compared to medium EDTA level indicating heavy metal toxicity. Also,the results demonstrated that high EDTA level (5.0 mmol kg−1) had a lethaleffect on plants. From all EDTA concentrations tested, 2.5 mmol kg−1 had thegreatest root to shoot Pb translocation. The use of EDTA in phytoremediationcould however be improved. Recently, Thayalakumaran et al. (2003) demon-strated that application of several small doses of EDTA is more effective inphytoremediation of copper contaminated soil than application of one largedose. More work is needed to examine if this applies to Pb-contaminated soil.

Phosphorus is relatively immobile in the soils (Read et al., 1997; Khanet al., 2000), and EDTA facilitated the uptake of P by plants. Studies suggest thatarbuscular mycorrhizal fungi (AMF) can also contribute to P uptake (Harrison,1997). The AMF are known to improve growth of plants by facilitating P uptakeby activities of external hyphae, which can grow out of the P-depletion zoneof the rhizosphere (Harrison and Van Buuren, 1995; Read et al., 1997; Khanet al., 2000). It is possible to lessen the P uptake process by suppressing AMF(Kahiluoto and Vestberg, 2000), therefore indirectly contributing to less metaltoxicity of plants (Hovsepyan and Greipsson, 2004). Thus, it is possible thataddition of EDTA along with suppressing AMF activity could facilitate highertranslocation and accumulation of Pb within plants. Therefore, further studiesin uptake of Pb by corn should include the potentially synergistic interactionbetween EDTA and AMF.

ACKNOWLEDGMENTS

The authors would like to thank Dr. P. Stewart for guidance; Dr. C. King for as-sistance with chemical preparation and analysis; and Dr. C. Vollrath for financialassistance.

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REFERENCES

Anderson, S., A. H. Chappelka, K. M. Flynn, and J. W. Odom. 2000. Leadaccumulation in Quercus nigra and Q. velutina near smelting facilities inAlabama, U.S.A. Water, Air, and Soil Pollution 118:1–11.

Blaylock, M. J., D. E. Salt, S. Dushenkov, O. Zakharova, C. Gussman, Y.Kapulnik, B. D. Ensley, and I. Raskin. 1997. Enhanced accumulation of Pbin Indian mustard by soil-applied chelating agents. Environmental Scienceand Technology 31:860–865.

Chaudhry, T. M., W. J. Hayes, A. G. Khan, and C. S. Khoo. 1998.Phytoremediation-focusing on accumulator plants that remediate metal-contaminated soils. Australasian Journal of Ecotoxicology 4:37–51.

Childs, J. 1979. Soil survey of Coffee County, Alabama. Washington, D.C.:USDA, Soil Conservation Service.

Cooper, E. M., J. T. Sims, J. W. Cunningham, J. W. Huang, and W. R. Berti.1999. Chelate-assisted phytoextraction of lead from contaminated soils.Journal of Environmental Quality 28:1709–1719.

Dekock, P. C., and R. L. Mitchell. 1957. Uptake of chelated metals by plants.Soil Science 84:55–62.

Deram, A., D. Petit, B. Robinson, R. Brooks, P. Gregg, and C. V. Halluwyn.2000. Natural and induced heavy-metal accumulation by Arrhenatherumelatius: Implications for phytoremediation. Communications in Soil Sci-ence and Plant Analysis 31:413–421.

Epstein, A. L., C. D. Gussman, M. Blaylock, U. Yermiyahu, J. W. Huang,Y. Kapulnik, and C. Orser. 1999. EDTA and Pb-EDTA accumulationin Brassica juncea grown in Pb-amended soil. Plant and Soil 208:87–94.

Foy, C. D., R. L. Chaney, and M. C. White. 1978. The physiology of metaltoxicity in plants. Annual Reviews of Plant Physiology 29:511–566.

Gibson, S. P., C. C. Morris, A. Hovsepyan, and S. Greipsson. 2002. Atmo-spheric deposition of lead in Troy, Alabama using lichens as bioindicators.Southeastern Biology. 49:209–210.

Gleba, D., N. V. Borisjuk, L. G. Borisjuk, R. Kneer, A. Poulev, M. Skarzhin-skaya, S. Duskenkov, S. Logendra, Y. Y. Glega, and I. Raskin. 1999. Useof plant roots for phytoremediation and molecular farming. Proceedingsof the National Academy of Sciences 96:5973–5977.

Greipsson, S. 1992. Effects of P on growth and uptake of Cu and Fe in ricegrown in excess Cu. International Rice Research Newsletter 17:19–24.

Greipsson, S. 1995. Effect of iron plaque on roots of rice on growth of plantsin excess zinc and accumulation of phosphorus in plants in excess copperand nickel. Journal of Plant Nutrition 18:1659–1665.

Greman, H., S. Velikonja-Bolta, B. Kos, and D. Lestan. 2001. EDTA enhancedheavy metal phytoextraction: Metal accumulation, leaching and toxicity.Plant and Soil 235:105–114.

Dow

nloa

ded

by [

Tuf

ts U

nive

rsity

] at

14:

38 1

7 O

ctob

er 2

014

EDTA of Lead-Contaminated Soil by Corn 2047

Harrison, M. J., and M. L. Van Buuren. 1995. A phosphate transporter from themycorrhizal fungus Glomus versiforme. Science 378:626–629.

Harrison, M. J. 1997. The arbuscular mycorrhizal symbiosis. In Plant-microbeinteractions, eds. G. Stacey and N. T. Keen, 1–34. London, U.K.: Chapman& Hall.

Hong, P. K. A., C. Li, S. K. Banerji, and T. Regmi. 1999. Extraction, recoveryand biostability of EDTA for remediation of heavy metal-contaminatedsoil. Journal of Soil Contamination 8:81–103.

Hovsepyan, A., and S. Greipsson. 2004. Effect of arbuscular mycorrhizal fungion phytoextraction by Zea mays of lead contaminated soil. InternationalJournal of Phytoremediation 6(4):305–321.

Huang, J. W., J. Chen, W. R. Berti, and S. D. Cunningham. 1997. Phy-toremediation of lead-contaminated soils: Role of synthetic chelates inlead phytoextraction. Environmental Science and Technology 31:800–805.

Huang, J. W., and S. D. Cunningham. 1995. Lead phytoextraction: Speciesvariation in lead uptake and translocation. New Phytologist 134:75–84.

Judah, L. S. 2004. Heavy metal contamination of soils at five polluted sites insoutheast Alabama, M.S. Thesis. Troy, Alamaba: Troy University.

Khan, A. G., C. Kuek, T. M. Chaudhry, C. S. Khoo, and W. J. Hayes. 2000. Roleof plants, mycorrhizae and phytochelators in heavy metal contaminatedland remediation. Chemosphere 41:197–207.

Kahiluoto, H., and M. Vestberg. 2000. Creation of a non-mycorrhizal controlfor a bioassay of AM effectiveness. 1. Comparison of methods. Mycorrhiza9:259–270.

Kirkham, M. B. 2000. EDTA-facilitated phytoremediation of soil with heavymetals from sewage sludge. International Journal of Phytoremediation2:159–172.

Kos, B., and D. Lestan. 2003. Influence of a biodegradable ([S,S]-EDDS) andnondegradable (EDTA) chelate and hydrogen modified soil water sorptioncapacity on Pb phytoextraction and leaching. Plant and Soil 253:403–411.

Lambert, M., G. Pierzynski, L. Erickson, and J. Schnoor. 1997. Remediationof lead-, zinc- and cadmium-contaminated soils. Issues in EnvironmentalScience and Technology 7:91–102.

Lange, O. L., P. S. Nobel, C. B. Osmond, and H. Ziegler. 1983. Toxicity and tol-erance in the responses of plants to metals. In Physiological plant ecologyIII, 246–289. New York: Springer-Verlag.

Luo, A., G. Jing, P. Wu, J. Ni, S. Jiang, and Y. Zhang. 1997. Rice genotypedifferences in nutrient status under excessive ferric-iron conditions. Journalof Plant Nutrition 20:1361–1373.

McGrath, S. P., F. J. Zhao, and E. Lombi. 2001. Plant and rhizosphere processesinvolved in phytoremediation of metal-contaminated soil. Plant and Soil232:207–214.

Dow

nloa

ded

by [

Tuf

ts U

nive

rsity

] at

14:

38 1

7 O

ctob

er 2

014

2048 A. Hovsepyan and S. Greipsson

Miller, R. O. 1998. High-temperature oxidation: dry ashing. In Handbook ofreference methods for plant analysis, ed. Y. P. Karla, 53–57. Boca Raton,Florida: Soil and Plant Analysis Council, Inc., CRC Press.

Read, D. J., D. H. Lewis, A. H. Fitter, and I. J. Alexander. 1997. Phospho-rus transport by external hyphae of vesicular-arbuscular mycorrhizas. InMycorrhizas in Ecosystems, 48–54. Wallingford, U.K.: CABI Publishing.

Ripley, E. A., R. E. Redmann, A. A. Crowder, T. C. Ariano, and R. J. Farmer.1996. Environmental effects of mining. Delray Beach, Florida: St. LuciePress.

Salt, D. E., M. Blaylock, P. B. A. N. Kumar, V. Dushenkov, B. D. Ensley,I. Chet, and I. Raskin. 1995. Phytoremediation: A novel strategy for theremoval of toxic metals from the environment using plants. Biotechnology13:468–474.

Stanhope, K. G., S. D. Young, J. J. Hutchinson, and R. Kamath. 2000. Use ofisotopic dilution techniques to assess the mobilization of nonlabile Cd bychelating agents in phytoremediation. Environmental Science and Technol-ogy 34:4123–4127.

Thayalakumaran, T., B. H. Robinson, I. Vogeler, D. R. Scotter, B. E. Clothier,and H. J. Percival. 2003. Plant uptake and leaching of copper during EDTA-enhanced phytoremedation of repacked and undisturbed soil. Plant and Soil254:415–423.

Walton, B. T., E. A. Guthrie, and A. M. Hoylman. 1994. Toxicant degradationin the rhizosphere. In Bioremediation through rhizosphere technology, eds.T.A. Anderson and J.R. Coats, Symposium Series 563, 11–26. Chicago,Illinois: American Chemical Society.

Weatherford, J., A. Hammond, and J. Ratliff. 1997. Investigation of the ability ofplants found in Western Kentucky to hyperaccumulate lead and aluminumfrom soils. Microchemical Journal 56:93–102.

Dow

nloa

ded

by [

Tuf

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] at

14:

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7 O

ctob

er 2

014