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Journal of Hazardous Materials 190 (2011) 810–815

Contents lists available at ScienceDirect

Journal of Hazardous Materials

journa l homepage: www.e lsev ier .com/ locate / jhazmat

inding characteristics of copper and cadmium by cyanobacterium Spirulinalatensis

inchuan Fanga, Chen Zhoub, Peng Caib, Wenli Chena, Xingmin Rongb, Ke Daib, Wei Liangb,i-Dong Guc, Qiaoyun Huanga,b,∗

State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, ChinaKey Laboratory of Subtropical Agricultural Resources and Environment, Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan30070, ChinaDepartment of Ecology & Biodiversity, The University of Hong Kong, Pokfulam Road, Hong Kong, China

r t i c l e i n f o

rticle history:eceived 8 February 2011eceived in revised form 24 March 2011ccepted 31 March 2011vailable online 7 April 2011

eywords:

a b s t r a c t

Cyanobacteria are promising biosorbent for heavy metals in bioremediation. Although sequestrationof metals by cyanobacteria is known, the actual mechanisms and ligands involved are not very wellunderstood. The binding characteristics of Cu(II) and Cd(II) by the cyanobacterium Spirulina platensiswere investigated using a combination of chemical modifications, batch adsorption experiments, Fouriertransform infrared (FTIR) spectroscopy and X-ray absorption fine structure (XAFS) spectroscopy. A signif-icant increase in Cu(II) and Cd(II) binding was observed in the range of pH 3.5–5.0. Dramatical decrease in

pirulina platensisu(II)d(II)equestration mechanismshemical modificationsAFS

adsorption of Cu(II) and Cd(II) was observed after methanol esterification of the nonliving cells demon-strating that carboxyl functional groups play an important role in the binding of metals by S. platensis. Thedesorption rate of Cu(II) and Cd(II) from S. platensis surface was 72.7–80.7% and 53.7–58.0% by EDTA andNH4NO3, respectively, indicating that ion exchange and complexation are the dominating mechanismsfor Cu(II) and Cd(II) adsorption. XAFS analysis provided further evidence on the inner-sphere complexa-tion of Cu by carboxyl ligands and showed that Cu is complexed by two 5-membered chelate rings on S.

platensis surface.

. Introduction

Land utilization of biosolids and applications of fertilizers andesticides have contributed to a continuous accumulation of heavyetals in many aquatic and near-surface systems [1]. The fate of

oxic metallic cations in environment depends largely on theirnteractions with microorganisms. The biomass of bacteria, fungi,easts and algae have been reported for effective and economicalemoval of a wide variety of toxic heavy metals from wastewa-er and engineering systems. Metal ions can be immobilized byunctional groups such as carboxyls, phosphomonoesters, phos-hodiesters, amines and hydroxyls that are native to the proteins,

ipids, and carbohydrates on the cell walls of organisms [2]. A better

nderstanding of how metal sorption takes place on the surfacesf microorganisms on molecular-scale is critical to elucidate theechanisms involved in terms of mobility, speciation and bioavail-

bility of metals in geological systems.

∗ Corresponding author at: State Key Laboratory of Agricultural Microbiology,uazhong Agricultural University, Wuhan 430070, China. Tel.: +86 27 87671033;

ax: +86 27 87280670.E-mail address: qyhuang@mail.hzau.edu.cn (Q. Huang).

304-3894/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.jhazmat.2011.03.122

© 2011 Elsevier B.V. All rights reserved.

Metal adsorption onto bacterial surfaces has been studiedextensively over the past 25 years. However, much of previousinvestigations have been focused either qualitative informationor have quantified adsorption using a bulk-partitioning approach,making it impossible to provide detailed information about metal-binding mechanisms [3]. Until 10 years ago, applications of XAFSspectroscopy to environmental science have grown significantly,resulting in a better delineating of metal adsorption processes andmechanisms onto bacteria. For example, Panak et al. [4,5] usedtime-resolved laser-induced fluorescence spectroscopy (TRLFS), inconjunction with XAFS, to demonstrate that U(VI) forms innersphere complexes only with phosphate groups on cell walls of anumber of Bacillus species at pH 4.5–5.0. Boyanov et al. [6] reportedthat Cd binds to the Bacillus subtilis predominantly due to phospho-ryl binding below pH 4.4, whereas with increasing pH (4.4–6.5),adsorption to carboxyl groups becomes increasingly important.Toner et al. [7] investigated Zn sorption by a bacterial biofilm ofPseudomonas putida at pH 6.9, and attributed zinc sorption to the

biofilm predominantly to Zn-phosphoryl complexes, with a rel-atively small contribution from carboxyl-type complexes. Guinéet al. [2] reported sulfhydryl ligands were responsible for Zn adsorp-tion to three Gram negative bacterial strains at low loadings ofZn. The above molecular-scale investigations demonstrated that

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L. Fang et al. / Journal of Hazar

orption of heavy metals onto bacteria is controlled by carboxyl,hosphoryl and perhaps sulfhydryl functional groups on the cellall of the microorganisms.

Among a large amount of information on bacteria, few studiesave been conducted on cyanobacteria. Until recently, cyanobacte-ia have been found to be of interest in metal adsorption processes.yanobacteria are photosynthetic prokaryotes commonly found

n natural environmental and are suggested to have some addeddvantages over other microorganisms for removing heavy metalsecause of their large surface area, greater mucilage volume withigh binding affinity and simple nutrient requirements [8]. Labo-atory and field studies have shown that cyanobacteria are highlyffective biological sorbents and represent an important sink foretals in aquatic settings [9–11]. To accurately predict the fate

f metals in cyanobacteria-inhabited environments, a quantitativend mechanistic understanding of metal-cyanobacteria sorptioneactions is needed. However, our current knowledge of metalptake by cyanobacteria is largely empirical and limited by a lackf molecular-scale information [12]. In this study, a combination ofhemical modifications, metal-binding experiments, infrared spec-roscopy and XAFS were performed to gain insights on the chemicalunctional groups that may be involved in the binding of Cu(II)nd Cd(II) by cyanobacterium Spirulina platensis. In addition, sometructural information was obtained to describe the complexationf Cu(II) with the functional groups involved. These investigationsimed to provide a more comprehensive understanding of theetal-cyanobacteria sorption reactions.

. Materials and methods

.1. Preparation of the cyanobacterium biomass

S. platensis was cultured at pH 7.5 in Medium BG-11Supplementary Table S1) under illumination of 400 �E m−2 s−1 at8 ◦C and 120 rpm. Five-day-cultured cells (late exponential phase)ere harvested and washed three times with deionized distilledater (DD H2O), then separated by centrifugation at 12,000 rpm

or 10 min, collected as native S. platensis cells.

.2. Chemical modification of the nonliving cells

The collected native cells were lyophilized overnight in a Lab-onco freeze dryer and then autoclaved at 121 ◦C for 30 min tobtain the nonliving cells [13,14]. The esterification of the nonlivingells was carried out according to the method of Gardea-Torresdeyt al. [15]. Specifically, 5.0 g nonliving cells of S. platensis were sus-ended in 250 mL of 99.9% acidic methanol solution and 3 mL ofoncentrated hydrochloric acid (HCl). The suspension was con-inuously stirred at 60 ◦C for 48 h and allowed to cool to roomemperature. The pelleted S. platensis cells were then washed threeimes with DD water in order to quench the esterification reaction,fter that lyophilized again for further metal binding experiments.he chemical esterification reaction is shown below, where R rep-esents all of the components in the nonliving cells [15–17].

COOH + CH3OHH+−→RCOOCH3 + H2O

ase hydrolysis of the nonliving cells was carried out in order toncrease the availability of carboxyl groups that may be involvedn the binding of heavy metals [18]. Three gram of nonliving cells

as reacted with 100 mL of 0.1 mol L−1 NaOH for 2 h to perform theollowing reaction:

COOCH3 + NaOHH+−→RCOO− + CH3OH + Na+

aterials 190 (2011) 810–815 811

After the reaction, the suspension was centrifuged and the super-natant was discarded. The cells were washed three times with DDwater, centrifuged, and lyophilized for metal binding experiments.

2.3. Fourier transformed infrared spectroscopy

The chemical characteristics of cyanobacterial cells (native andesterified nonliving cells of S. platensis) were analyzed using aFourier transformed infrared spectrometer (Nicolet AVAR 330). Allinfrared spectra were recorded over the range of 4000–400 cm−1

and the averaged spectra were obtained at a resolution of 4 cm−1.Sample disks were made from 5 mg of cyanobacterial cells encap-sulated in 150 mg of KBr.

2.4. Metal solution

All chemicals used in this study were of analytical gradeand solutions were prepared using DD water. Stock solutionsof Cu(II) and Cd(II) (1000 mg L−1) were prepared by dissolvingCu(NO3)2·3H2O and Cd(NO3)2·4H2O in DD water. A few drops of0.1 mol L−1 HNO3 were added to the solutions to prevent the pre-cipitation of Cu(II) and Cd(II) by hydrolysis. The initial pH of theworking solutions was adjusted to 5.0 for Cu(II) and 6.0 for Cd(II)binding experiment by the addition of 0.1 mol L−1 HNO3 and NaOHsolution.

2.5. Metal adsorption experiments

Biosorption experiments were conducted at 25 ◦C in batch with0.01 g of the native and chemical modified S. platensis cells in a50 mL plastic tube containing 20 mL of working solution volume.The initial pH of the working solutions was adjusted to 5.0 for Cu(II)and 6.0 for Cd(II) binding experiment by addition of 0.1 mol L−1

HNO3 and NaOH solution. The final metal concentrations for Cu(II)and Cd(II) were 100 mg L−1 and 60 mg L−1, respectively. Potassiumnitrate (0.01 mol L−1) was used as a supporting electrolyte for allexperiments. The mixture was shaken for 2 h and then centrifuged.After centrifugation at 12,000 rpm for 10 min, the concentration ofmetal in the supernatant was analyzed by flame atomic absorptionspectrometry (Varian AAS240FS). The difference between the initialmetal ion concentration and the remaining metal ion concentrationwas assumed to be adsorbed by S. platensis cells. Adsorption wasalso conducted in the range of pH from 2.0 to 5.0 for Cu(II) and 2.0to 6.0 for Cd(II). No precipitation of metals occurs by hydrolysis inthe pH range explored according to the calculated pH values forthe precipitation of the hydroxyl complexes of copper (5.7) andcadmium (8.5). All experiments were conducted in triplicate.

2.6. Desorption of Cu(II) and Cd(II)

Desorption of Cu(II) and Cd(II) from previously loaded nativeS. platensis was studied by using DD water, 0.1 mol L−1 of EDTAand 1.0 mol L−1 of NH4NO3 as eluent. For this purpose, the pre-viously prepared S. platensis cells loaded with Cu(II) or Cd(II) wasadded to 20 mL of eluent in a 50 mL plastic tube in the presenceof 0.01 mol L−1 of KNO3. After 2 h of shaking at 25 ◦C, supernatantsafter centrifugation were analyzed for the Cu(II) and Cd(II) concen-trations. The same procedure was repeated three times. Desorption

ratio was calculated from the amount of metal ions adsorbed on thecyanobacteria and the final metal ion concentration in desorptionmedium. Control experiments without cyanobacteria were carriedout in order to determine the extent of adsorption of Cu(II) andCd(II) from solution by the plastic tube.

8 dous Materials 190 (2011) 810–815

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40

50

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tent

ial

(mv)

pH

Cu Cd

-60

-50

-40

-30

-20

-10

0

10

20

30

Zeta potential

Fig. 1. pH profile for Cu(II) and Cd(II) adsorption on the native S. platensis and thezeta potential of S. platensis in the presence of 0.01 M KNO3 at different pH valuesand 25 ◦C.

Cu(II) Cd(II)

20

30

40

50

60

70

Met

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adso

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(m

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Native

Hydrolysis

Esterification

12 L. Fang et al. / Journal of Hazar

.7. Zeta potential measurements

The suspension for zeta potential measurements was preparedy mixing the native S. platensis cells (1 g L−1) with 0.01 mol L−1

NO3 solution (25 mL). The solution pH was adjusted to 2.0–6.0sing 0.1 mol L−1 of HNO3 or NaOH and then analyzed by Zetaotential Analyzer (Brookhaven Instruments Corporation, USA).hree independent zeta potential measurements were collected forach sample to ensure accurate and reproducible data.

.8. X-ray absorption spectra measurement

Copper K-edge X-ray absorption spectra at 8979 eV wereecorded on beamline U7c at the National Synchrotron Radiationaboratory (NSRL, China). The electron beam energy was 0.8 GeVnd the mean stored current was 100 mA. The energy of X-ray wasetuned by using a fixed-exit double-crystal Si (1 1 1) monochro-ator. Ionization chambers with N2 atmosphere were used to

ollect the Fe K-edge spectra at room temperature. To calibrate X-ay energies, a Cu foil internal reference was used with the firstnflection point set at 8979.0 eV. To determine the most proba-le configuration of Cu in our sorption sample, reference spectraere measured from standard compounds CuCl, CuS, Cu3PO4 and

.1 mol L−1 aqueous Cu(OAc)2·H2O (Sigma Chemicals). The XASata of the samples and aqueous complex reference were col-

ected using fluorescence mode with a Lytle detector, while thebsorptions of solid standard compounds were measured by trans-ittance mode. The XAFS data analysis was performed with theSRL-XAFS software [19]. The XAFS oscillations were isolated from

he raw, averaged data by removal of the pre-edge background,pproximated by a first-order polynomial. The extracted XAFSpectra, obtained via spline fitting techniques and normalized usingVictoreen function, were Fourier transformed (FT) using the k

ange 2.6–12.0 A−1. The theoretical scattering phases and ampli-udes used in data analysis were calculated with the scattering codeEFF 7 [20] using the five-membered Cu(II) ring structure [21].

. Results and discussion

.1. FTIR spectra analysis

The chemical characteristics of native and esterified S. platen-is cells are shown in Supplementary Fig. S1. The spectral featuresor bacteria are well established and the bands assignments areased on the Refs. [22–25]. The spectrum of native cells showed twoigh frequency bands (1656 cm−1 and 1540 cm−1) correspondingo amide I and amide II, respectively. A small band correspond-ng to symmetric stretching of COO− groups was observed at402 cm−1, which may derive from proteins and carboxylatedolysaccharides. Additional information on phospholipids alongith phosphodiesters, free phosphate, and monoester phosphate

unctional groups were observed near 1238 and 1082 cm−1, corre-ponding to >P O double bond asymmetric stretching frequencies.hese data showed the presence of carboxyl, amino and phos-hate groups on the native cells of S. platensis. In contrast tohe native cells, the band near 1402 cm−1 (–COO−) was appar-ntly disappeared and one new band at 1731 cm−1 (ester carbonyl)as clearly observed for the esterified nonliving cells. These dif-

erences demonstrated that the carboxyl groups on S. platensis

urfaces were transformed through esterification reaction. Further-ore, the bands between 1656–1540 cm−1 and 1238–1082 cm−1

ere nearly unaffected after esterification reaction, indicating thatsterification had no effects on other functional groups and theyanobacterial structures remained intact.

Treatments

Fig. 2. The adsorptions of Cu(II) and Cd(II) on native, nonliving and chemicallymodified nonliving S. platensis in the presence of 0.01 M KNO3 and at 25 ◦C.

3.2. Effect of pH on metal adsorption

Proton environment (pH) is an important factor affecting thebiosorption of heavy metals due to the influence of pH on the depro-tonation of metal-binding functional groups as well as the surfacecharge on the cyanobacteria. As shown in Fig. 1, the amount ofCu(II) and Cd(II) adsorption on untreated cyanobacteria increasedwith pH from 2.0 to 5.0 or 6.0, which is ascribed to the exposi-tion of more negative charges on the S. platensis cells as showedin the zeta potential curves. Furthermore, significant increases inthe binding of Cu(II) and Cd(II) were also observed in the rangeof pH 3.5–5.0, indicating that the functional groups at pKa 3.5–5play an important role in the adsorption of Cu(II) and Cd(II) on S.platensis cells. Based on typical deprotonation constants for short-chained carboxylic (4 < pKa < 6), phosphoric (pKa ≈ 7) and hydroxy(or phenolic) acids (9 < pKa < 11) [26], the increased metal bind-ing at higher pH was due to the deprotonation of carboxylicgroups.

3.3. Effect of chemical modification on metal adsorption

The adsorptions of Cu(II) and Cd(II) on native, nonliving andchemically modified nonliving cells are presented in Fig. 2. Thebinding capacity by the native cells for Cu(II) and Cd(II) were

L. Fang et al. / Journal of Hazardous Materials 190 (2011) 810–815 813

Cu(II) Cd(II)

0.0

0.2

0.4

0.6

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S. platensis

complexed by carboxyl groups on S. platensis surface, forming a

ig. 3. The percentage of Cu(II) and Cd(II) released from S. platensis cells after treat-ent with DD water, 0.1 mol L−1 of EDTA and 1.0 mol L−1 of NH4NO3.

7.8 mg kg−1 and 45.1 mg kg−1, respectively. Esterified nonlivingells resulted in the reduction in the binding of Cu(II) and Cd(II) by5.5 and 45.6%, respectively. After hydrolysis, the binding capac-

ties for Cu(II) and Cd(II) by S. platensis increased slightly due tohe formation of new carboxyl ligands. These results indicatedhe carboxyl groups play the most important role in the bind-ng of Cu(II) and Cd(II) from solution which was supported byhe increased adsorption capacity at pH from 3.5 to 5.0. Fur-hermore, a similar binding capacity between the native andonliving cells also suggested that active uptake was insignificant

n the overall mechanism of biosorption. Although cyanobacteriare Gram-negative in cellular structure, their cell walls containthick structural layer of peptidoglycan and an extended gly-

oproteins and polysaccharides [27], which are the main sourcef reactive carboxyl groups on the surfaces of cyanobacteria28]. Therefore, our data demonstrated that carboxyl groups onhe S. platensis cell wall are the dominant sink for Cu(II) andd(II).

.4. Desorption of Cu(II) and Cd(II)

Fig. 3 shows the percentage of Cu(II) and Cd(II) released from. platensis cells after treatment with different desorbents. Only.5–3.6% of Cu(II) and Cd(II) on S. platensis surface were removedy DD water. It suggested that the bound metal ions were not eas-

ly released and the contribution of physical adsorption was minor.he biosorption of Cr3+, Cd2+ and Cu2+ by blue-green algae Spirulinapecies also showed that the maximum contribution of physicaldsorption was only 3.7% [29]. The desorption rate of Cu(II) byH4NO3 and EDTA was 53.7% and 72.7%, respectively. Higher des-rption percentage by EDTA and NH4NO3 was observed for Cd(II)58.0% and 80.7%, respectively). Metal ions released by NH4NO3an be regarded as the fraction adsorbed by ion exchange, whilehat released by EDTA are considered as that adsorbed by com-lexation [30]. This implied that Cu(II) and Cd(II) was adsorbedredominantly by ion exchange and complexation on the surface of. platensis. In addition, esterified nonliving cells resulted in higherercentages of reduction in the binding of Cu(II) (55.5%) than Cd(II)45.6%), suggesting that carboxyl groups play a more important role

or Cu(II) adsorption. Therefore, the lower desorption percentagef Cu(II) as compared with that of Cd(II) leads us to speculate thatore carboxyl groups are involved in the complexation with Cu(II)

han Cd(II).

Energy (eV)

Fig. 4. Cu K-edge XANES spectra of sample and reference compounds.

3.5. X-ray absorption fine structure (XAFS) data analysis

The X-ray absorption near edge structure (XANES) has beenused successfully to determine the oxidation state and the chem-ical coordination environment of ions in different systems [31].The Cu K-edge XANES spectra from the samples and standardsused in this investigation are shown in Fig. 4. The adsorption edgeof sample was very similar to that of Cu(II) model compoundsCu(OAc)2·H2O, Cu3(PO4)2 and CuS, indicating that the oxidationstate of copper was not changed upon binding to S. platensis surface.As shown in Fig. 5, the extended X-ray absorption fine structure(EXAFS) spectra of samples (both in k and R space) were similarto those of Cu(OAc)2·H2O, but different from those of Cu3(PO4)2,CuCl or CuS. The similar spectra between the sample and standardcompounds containing Cu-carboxyl suggest the predominant for-mation of C–O–Cu bond between copper and the cyanobacterialcells.

To gain more insight into the molecular structure of the adsorp-tion of Cu on S. platensis surfaces, the EXAFS spectrum was fittedand presented in Figs. S2 and S3. The coordination number (CN),atomic separation distance (R), and EXAFS Debye–Waller factor(�2) obtained are listed in Table 1. The results indicated that Cuwas coordinated by 4 O atoms at an average distance of 1.94 A inthe first shell. The EXAFS studies of well-defined compounds haveshown that Cu(II) is usually 6 coordinated in the first coordina-tion shell, with 4 O or N atoms at distances of 1.90–1.97 A, and2 axial O atoms at 2.15–2.78 A [32,33]. In this research, the axial-ligand backscattering pair was not included in the fitting routinebecause of their high degree of disorder and thus minimal EXAFScontributions [33,34]. Therefore, these four atoms at shorter dis-tance surrounding Cu are most likely positioned in the equatorialplane of a Jahn–Teller distorted elongated octahedron. As for thesecond shell, Cu was found to be coordinated to 4.1 C atoms at adistance of 2.76 A. This provided direct evidence for inner-spherecomplexation of Cu by carboxyl ligands on S. platensis surface. Basedon the known structure of Cu organic monodentate and bidentateorganic Cu complexes [35], the bonding environment of a bis-five-membered carboxyl chelate with Cu was very similar to our data.Therefore, our final fitting results strongly suggested that Cu(II) is

structure involving two five-membered chelate rings (Fig. 6). Ascompared with the previous XAFS studies reported in Table 1, ourdetermined the coordination number and atomic separation dis-tance are in agreement with that of the complexation of Cu(II) in

814 L. Fang et al. / Journal of Hazardous Materials 190 (2011) 810–815

Table 1EXAFS fit results of Cu adsorption on S. platensis cells. Compared to values reported for Cu in glycine (PMG), aquatic humic acid (HA) and soil organic matter (SOM).

Samples Atomic backscatter R (Å)a �2(Å2)b CNc �E0 (eV)d Rfe

S. platensisShell 1 Cu–O 1.95 0.0049 4.0 1.50 0.041Shell 2 Cu–C 2.76 0.0081 4.1 -8.87 0.060

PMGf

Shell 1 Cu–O 1.96 – 4 – –Shell 2 Cu–C 2.81 3

Aquatic HAg

Shell 1 Cu–O 1.94 – 4.4 – –Shell 2 Cu–C 2.88 2.9

SOMh

Shell 1 Cu–O 1.92–1.95 – 4 – –Shell 2 Cu–C 2.76–2.84 2–4

a Atomic separation distance.b Debye–Waller factor coefficient.c Coordination number.d Energy shift.e Residual factor = �k(k3xexp − k3xcalc)/�k(k3xcalc), which measures the quality of the model Fourier-filtered contribution (xcalc) with respect to the experimental contribution

(xexp). The amplitude reduction factor (S20) was set to 0.75. For the first shell, coordination numbers (CN) was fixed 4.0.

f Ref. Sheals et al. [33].g Ref. Lee et al. [34].h Ref. Karlsson et al. [21].

2 4 6 8 10

a

b

12

CuCl

CuS

Cu3(PO4)2

Cu(OAc)2

S. platensis

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S. platensis

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Fig. 5. k3-Weighted EXAFS spectra for Cu in sample and reference compounds. (a)k space; (b) R space.

Fig. 6. Proposed model for Cu complexed by two 5-membered chelate rings in sam-ple. The more distant axial oxygens (Oax) are not included in the final fits to theEXAFS data.

aquatic humic acid and soil organic matter. The modeling of EXAFSdata for the complexation of solid and dissolved natural organicmatter suggested that Cu forms complexes consisting of one or twofive-membered chelate rings [21]. To our knowledge, data obtainedin this study are the first to directly determine the binding mech-anism of Cu(II) on cyanobacteria using XAFS technique, providingkey information about the metal–microorganisms interactions atmolecular level.

4. Conclusions

Our results demonstrated that the carboxyl groups play a vitalrole in the adsorption of Cu(II) and Cd(II) to the cyanobacteriumS. platensis. Ion exchange and complexation are the dominat-ing mechanisms for Cu(II) and Cd(II) adsorption. XAFS analysisrevealed that Cu(II) forms inner-sphere complexes consisting oftwo five-membered chelate rings on the cyanobacterial surface.The elucidation of the binding mechanisms for Cu(II) and Cd(II) on S.platensis cells at the molecular scale may help to accurately predictthe fate of metals in cyanobacteria-inhabited environments.

Acknowledgments

This work was financially supported by the National Natural Sci-ence of Foundation of China (40825002) and Huazhong AgriculturalUniversity Scientific & Technological Self-innovation Foundation(2009YB005). We gratefully acknowledge Dr. Bo He and Dr. Zhi Xie

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NSRL, USTC, China) for their helpful technical assistance of XAFSxperiments. We also thank Dr. Torbjörn Karlsson from Swedishniversity of Agricultural Sciences for XAFS data processing.

ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at doi:10.1016/j.jhazmat.2011.03.122.

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