Simultaneous Removal of Polycyclic Aromatic Hydrocarbons and Copper from Soils using Ethyl...

1591

A new approach using aqueous ethyl lactate-modifi ed [S,S]-ethylenediaminedisuccinic acid (EDDS) washing solutions was examined in the laboratory for the simultaneous removal of phenanthrene, pyrene, and Cu from contaminated soils. Ethyl lactate demonstrated greater solubilization effi ciency for phenanthrene and pyrene than ethanol. Th us ethyl lactate has a great potential for extracting polycyclic aromatic hydrocarbons (PAHs) from contaminated soils. For soils with varying properties, removal effi ciencies were found to be negatively correlated with soil organic carbon contents. Aqueous EDDS solution eff ectively extracted Cu from soils. Th e extraction effi ciency reached about 36.7% at a EDDS:Cu molar ratio of 5. Th e addition of ethyl lactate in EDDS solution (EDDS/Cu molar ratio = 2) effi ciently enhanced the extraction of the PAHs and also signifi cantly increased the Cu removal from 34.8 to 42.9%. Th e latter was mainly attributed to the fact that ethyl lactate increases the stability constant for Cu-EDDS complexes, hence shifting the degree of desorption of Cu from soil. Sequential extraction indicated that the EDDS/ethyl lactate solution extracted Cu primarily from the acid extractable fraction, the reducible fraction and the oxidizable fraction. Th e results suggest that simultaneous removal of PAHs and heavy metals from contaminated soils is feasible by soil washing using an aqueous EDDS solution enhanced with ethyl lactate.

Simultaneous Removal of Polycyclic Aromatic Hydrocarbons and Copper from Soils

using Ethyl Lactate-Amended EDDS Solution

Yuanyuan Sun, Liangliang Ji, Wei Wang, Xiaorong Wang, and Jichun Wu Nanjing University

Hui Li Michigan State University

Hongyan Guo* Nanjing University

Heavy metals are often co-contaminants with organic pollutants

such as benzene, toluene, ethylbenzene, xylene (BTEX), and

PAHs in soils/sediments (Ahtiainen et al., 2002; Maliszewska-

Kordybach and Smreczak, 2003). Th e U.S. Environmental

Protection Agency (USEPA, 1997) reported that 41% of the national

priority list (NPL) sites are contaminated with both heavy metals and

PAHs. It is critical to develop effi cient and cost-eff ective approaches

to remove such mixed contaminants from soils. Several physical,

chemical, and biological techniques as well as combinations of them

have been developed or are currently being developed to remediate

contaminated soils (Semer and Reddy, 1996; Mulligan et al., 2001a).

Among these techniques, soil washing is an attractive remediation

technology (Semer and Reddy, 1996; Peters, 1999). Th e advantage

of this method is that the operation is relatively simple compared

to other technologies, and that high extraction effi ciency for specifi c

contaminants can be achieved if appropriate extractants are selected

(Griffi ths, 1995; Semer and Reddy, 1996; Peters, 1999).

Selection of an environmentally friendly and effi cient extract-

ant is essential to ensure the success of soil washing. For organic

contaminants anionic and nonionic surfactants have been widely

used in soil cleanup due to the enhanced solubilization and mobi-

lization (Mulligan et al., 2001b). Heavy metal contamination is of-

ten treated with chelating agents, such as citric acid, nitrilotriacetic

acid (NTA), and ethylenediaminetetraacetic acid (EDTA), among

which EDTA is the most widely used so far (Hauser et al., 2005).

In recent years, simultaneous removal of organic and inorganic con-

taminants has been studied. Semer and Reddy (1996) showed that

a combination of 1.25 mol L–1 sulfuric acid and isopropyl alco-

hol at a ratio of 4:9 removed mixed pollutants effi ciently and eco-

nomically. Chatain et al. (2004) found that using carboxylmethyl-β

cyclodextrin as a fl ushing agent to enhance the removal of both

inorganic and organic pollutants from mixed-contaminated soils is

a promising remediation method. Lee et al. (2005) studied simul-

taneous removal of organic and inorganic contaminants by micellar

enhanced ultrafi ltration with surfactant mixtures.

Abbreviations: EDDS, [S,S]-ethylenediaminedisuccinic acid; EDTA,

ethylenediaminetetraacetic acid; NTA, nitrilotriacetic acid; PAHs, polycyclic

aromatic hydrocarbons.

Y. Sun and J. Wu, State Key Lab. of Pollution Control and Resource Reuse, Dep.

of Hydrosciences, Nanjing Univ., Nanjing, 210093, China; L Ji, W. Wang, X. Wang,

and H. Guo, State Key Lab. of Pollution Control and Resource Reuse, School of the

Environment, Nanjing Univ., Nanjing, 210093, China; H. Li, Dep. of Crop and Soil

Sciences, Michigan State Univ., East Lansing, MI 48824.

Copyright © 2009 by the American Society of Agronomy, Crop Science

Society of America, and Soil Science Society of America. All rights

reserved. No part of this periodical may be reproduced or transmitted

in any form or by any means, electronic or mechanical, including pho-

tocopying, recording, or any information storage and retrieval system,

without permission in writing from the publisher.

Published in J. Environ. Qual. 38:1591–1597 (2009).

doi:10.2134/jeq2008.0374

Received 19 Aug. 2008.

*Corresponding author ([email protected]).

© ASA, CSSA, SSSA

677 S. Segoe Rd., Madison, WI 53711 USA

TECHNICAL REPORTS: ECOSYSTEM RESTORATION

1592 Journal of Environmental Quality • Volume 38 • July–August 2009

A potential matter of concern with soil washing is that a

portion of the applied chemicals may remain in the soil and

could spread into the environment when the treated soil is re-

turned to the original or a new site. Acid washing can be lethal

to the soil microfl ora and destruct soil physical structures and

chemical properties (Pichtel and Pichtel, 1997; Moutsatsou et

al., 2006). Methylated β-cyclodextrin was found to be signifi -

cantly alter soil physical properties (Jozefaciuk et al., 2003). Th e

EDTA is quite resistant to biodegradation and thus can persist

for extended times in the environment (Bucheli-Witschel and

Egli, 2001; Nowack, 2002). Nitrilotriacetic acid is readily bio-

degradable, but carcinogenic and, therefore, not recommended

for remediating contaminated soils (Peters, 1999).

Recently, EDDS has been proposed to replace EDTA be-

cause it has a similar chelating ability as EDTA, but is much

more readily biodegraded (Schowanek et al., 1997; Jaworska et

al., 1999; Van Devivere et al., 2001; Hauser et al., 2005; Tandy

et al., 2006a, 2006b). In a recent study, Tandy et al. (2004)

showed that EDDS extracted about 60% Cu from soil at pH

7 while EDTA extracted only 38% at an equimolar ratio of

chelating agent to metal. In addition, after a lag phase of 7 to

11 d, EDDS was found to degrade with a half-life of 4.2 to 5.6

d in the soil after the washing process (Tandy et al., 2006a).

Th e aim of this study was to test the potential use of a mix-

ture of EDDS and an organic solvent for the simultaneous re-

moval of organic contaminants and heavy metals from soils.

Khodadoust et al. (1999, 2000) demonstrated the eff ectiveness

of ethanol/water mixtures in extracting PAHs and other or-

ganic pollutants. As a potential alternative to ethanol, we chose

ethyl lactate in this study. Lactate esters are a class of environ-

mental-friendly solvents that are used in food, pharmaceutical,

and cosmetic preparations (Clary et al., 1998). Ethyl lactate is

recognized as a “green solvent” owing to numerous attractive

properties including strong solvency power, low toxicity, and

high biodegradability. It is easy to recycle, noncorrosive, non-

carcinogenic, nondestructive to atmospheric ozone, and rela-

tively inexpensive (Bowmer et al., 1998; Clary et al., 1998).

Th ese properties make it an attractive cosolvent to be used also

in extracting organic contaminants from soils.

Phenanthrene and pyrene were chosen to represent organic

contaminants and Cu to represent heavy metal contamina-

tion. A series of batch extraction experiments were performed

to determine the effi ciency of EDDS/ethyl lactate mixtures to

remove phenanthrene, pyrene, and Cu from soils.

Materials and Methods

SoilsFour diff erent soils were collected for this study, which were

representative of typical soils encountered in East, Central, and

Northeast China. Soil A and B were collected from agricultural

fi elds in the Kaifeng area of Central China and the Shenyang area

of Northeast China, respectively. Soils C and D were collected

from an agricultural fi eld and a Cu mine in the Tangshan area of

East China, respectively. According to the soil classifi cation system

developed by the U.S. Department of Agriculture (Watts, 1998)

all soils were silty loams. Soils A, B, and C had very moderate Cu

levels, whereas soil D was heavily contaminated with Cu. None of

the four soils was contaminated with organic pollutants or other

heavy metals than Cu. Th e soil material used in the experiments

was taken from the top 20-cm layer, air-dried, and then passed

through a <2-mm sieve before use. Th e pH of the soil was mea-

sured in a 0.01 mol L–1 CaCl2 solution at a 1:2.5 ratio of soil/solu-

tion (w/v) using a pH meter. Th e soil texture and organic carbon

content were measured by the procedures described by Avery and

Bascomb (1982). Selected physicochemical properties of the col-

lected samples are given in Table 1.

Phenanthrene and pyrene were dissolved in acetone and

thoroughly mixed with the soil samples to prepare PAH-con-

taminated samples. Th e acetone was then allowed to evaporate

completely. After drying the soil samples were transferred to

glass bottles and aged for 2 wk. Th e resulting contaminated

soils (A, B, C, and D2) had fi nal concentrations of 63.0, 72.4,

75.2, and 79.3 mg kg–1 for phenanthrene, and 84.9, 88.9, 90.8,

and 95.8 mg kg–1 for pyrene. Soil D not spiked with PAHs was

labeled as D1 in the study.

Th e total Cu concentration was determined by digesting

the soil samples using 4:1 concentrated HNO3 and HClO

4

(v/v) (Li et al., 2001), and was quantifi ed with a Th ermo fl ame

Atomic Absorption Spectrophotometer (AAS). Sequential ex-

traction for Cu in soil was conducted following the scheme

proposed by the Commission of the European Communities

Bureau of Reference (BCR). Th is scheme consists of extrac-

tions using 0.1 mol L–1 acetic acid (CH3COOH, pH = 2.85),

0.1 mol L–1 hydroxyl ammonium chloride (NH2OH·HCl,

pH = 2), Hydrogen peroxide (H2O

2) + 1 mol L–1 ammonium

acetate (NH4Ac, pH = 2), and aqua regia (3HCl + 7HNO

3),

which corresponded to the fraction of acid soluble, reducible,

oxidizable, and residual. Th e detailed method was reported by

Quevauviller et al. (1993).

SolubilizationSolubility enhancement for phenanthrene and pyrene was

evaluated by measuring solubilities in aqueous ethyl lactate or

ethanol mixtures. Aliquots of 10 mL aqueous solution contain-

ing diff erent percentages of ethyl lactate or ethanol (0, 0.5, 1,

2, 5, 10, and 20%) were fi lled into 22-mL Corex centrifuge

tubes with Tefl on-lined screw caps. An excess of phenanthrene

(or pyrene) crystals was added to each tube according to the

results of a preliminary experiment. Th e mixtures were equili-

brated on a shaker at 150 rpm for 24 h at 25 ± 1°C, and then

centrifuged at 4000 rpm for 30 min. Similar experiments were

conducted to assess the eff ects of EDDS and Cu/EDDS com-

binations on the solubility of phenanthrene and pyrene. In

these experiments, EDDS was added at concentrations ranging

from 1.85 to 9.23 mmol L–1, and Cu (Cu (NO3)

2) at concen-

trations ranging from 0.74 to 3.69 mmol L–1 combined with

3.69 mmol L–1 EDDS in water/cosolvent mixture (8~12%), re-

spectively. All experiments were conducted in three replications.

Th e concentration of phenanthrene and pyrene in the solution

was determined by a Hewlett-Packard 1100 High-Performance

Liquid Chromatograph (HPLC) equipped with a photodiode

Sun et al.: PAHs and Cu Removal from Soils Using Mixed EDDS/Ethyl Lactate Solution 1593

array detection (DAD) and a Agilent Zorbax Eclipse XDB-C8

(4.6 mm i.d ×150 mm length). Th e mobile phase was an iso-

cratic mixture containing methanol-water (80:20) with a fl ow

rate at 1 mL min–1. Th e DAD wavelengths were set at 252 nm

for phenanthrene and 238 nm for pyrene (Yang et al., 2006).

ExtractionExtraction experiments were performed using the batch

equilibration technique at 25 ± 1°C. One-gram aliquots of

contaminated soil (A, B, C, and D2) were mixed in Corex cen-

trifuge tubes with 10 mL of aqueous ethyl lactate or ethanol

solution of diff erent concentrations (0, 0.5, 1, 2, 5, 10, and

20%). All samples were prepared in triplicates. Th e mixtures

were then shaken at 150 rmp for 24 h, and centrifuged at 4000

rpm for 30 min. Th e concentrations of phenanthrene, pyrene,

ethyl lactate, and ethanol in the supernatant were measured by

means of HPLC.

Samples of soil D1, which contained 1083 mg kg–1 of Cu,

were prepared in the same way as described before with ethyl

lactate. In addition, D1 samples were also prepared to inves-

tigate extraction with EDDS. For this purpose, 1-g aliquots

were mixed with 10 mL of 1.9, 3.7, 5.5, 7.4, and 9.2 mmol L–1

EDDS solution, resulting in EDDS/Cu molar ratios of 1, 2, 3,

4, and 5, respectively. Otherwise, the samples were treated as

described before. Copper concentrations were determined by

means of AAS.

To examine the effi ciency of simultaneous removal of PAHs

and Cu, 1-g samples of soil D2 were extracted with 10 mL of

a 3.7 mmol L–1 of EDDS solution (EDDS/Cu molar ratio = 2)

containing diff erent levels of ethyl lactate (0, 0.5, 1, 2, 5, 10,

and 20%). Th e solution phase of these samples was analyzed

for phenanthrene and pyrene by means of HPLC and for Cu

by means of AAS. As in the other experiments all extractions

were performed in triplicates.

Eff ect of Ethyl Lactate on the Stability

of Copper-EDDS ComplexPotentiometer titration was used to measure the condi-

tional stability constant of Cu-EDDS. Temperature was con-

trolled by a thermostatic bath at 25 ± 0.1°C. Ethyl lactate was

added at various concentrations to a cell containing 50 mL of

1.00 mmol L–1 EDDS and 1.00 mmol L–1 Cu. After thermal

equilibrium was reached, the solution in the cell was titrated

under magnetic stirring with 0.1 mol L–1 KOH standard so-

lution. During titration, disturbance by carbon dioxide was

avoided by purging the system with N2. Th e experiment was

conducted in three to fi ve replicates. Th e reproducibility of the

titration was within 0.02 pH units. Th e BEST program was

used to calculate and optimize the stability constant (Martell

and Motekaitis, 1992).

Statistical AnalysisData are given as means ± standard deviations (SD). Signifi cant

diff erences (P < 0.05) were determined using Student’s t test.

Results and Discussion

Solubilization of Phenanthrene and PyreneApparent solubilities (S

w*) of phenathrene and pyrene in

aqueous ethyl lactate or ethanol mixtures are shown in Fig.

1. At an ethyl lactate concentration of 20% the solubility was

39.9 mg L–1 for phenanthrene and 9.2 mg L–1 for pyrene.

Th is was two to three times the solubility of phenanthrene

(19.5 mg L–1) and pyrene (3.5 mg L–1) at the same concentra-

tions of ethanol. Th e presence of EDDS and Cu-EDDS com-

plexes did not show an eff ect on the solubility of phenanthrene

and pyrene (data not shown).

Th e solubilization power of a cosolvent is usually described

by a log-linear model (Millard et al., 2002):

log Sw* = log S

w + σ f

c [1]

where Sw* and S

w are the aqueous solubilities of the organic

compound in presence and absence of the cosolvent, respectively,

σ is the cosolvent solubilization power, and fc is the volume

fraction of cosolvent in the cosolvent-water mixture.

Th e σ values obtained here for phenanhrene and pyrene are

7.7 and 12.4 in ethyl lactate/water mixture, and 4.7 and 7.6 in

ethanol/water mixture. Th us, ethyl lactate manifested a greater

capacity to enhance PAH solubility than ethanol. Th e organic

contaminant removal effi ciently from soil is positively correlated

to the extent of solubility enhancement of the cosolvent (Yang

et al., 2006). Surfactants were found to exhibit even higher

solubilization power than ethyl lactate (Yang et al., 2006; Zhou

and Zhu, 2007). However, surfactants or their biodegradation

products often are not environmentally safe. Although many

surfactants are of low toxicity to humans, they may still nega-

tively aff ect animals and plants (Mulligan et al., 2001b).

Extraction of Polycyclic Aromatic Hydrocarbons from SoilAs Fig. 2 shows, the ethyl lactate/water solutions manifested

greater extraction effi ciency for PAHs than the ethanol/water solu-

tions, which agree with the fi nding that ethyl lactate also showed a

greater solubilization effi ciency for phenanthrene and pyrene than

ethanol. Cosolvents can facilitate solubilization of a nonpolar sol-

ute by reducing the polarity of the aqueous solution surrounding

the molecules of the solute (Millard et al., 2002). Th is explains

how ethyl lactate is able to enhance the dissolution of hydrophobic

organic compounds (such as PAHs) in an aqueous solution. Th e

mixture containing 20% of ethyl lactate removed nearly 100% of

phenanthrene from soil A and C, 66.0% from soil B, and 65.0%

from soil D2. For the aqueous solution containing 20% ethanol

the extraction effi ciencies for phenanthrene were 94.2, 38.3, 71.2,

Table 1. Selected physicochemical properties of the soils used in this study.

Soil pH Sand Silt Clay Organic C content Total Cu

–––––––––––––––%––––––––––––––– mg kg–1

A 7.8 7.1 82.1 10.8 0.79 42.8

B 6.0 2.3 85.2 12.5 1.88 29.6

C 7.4 20.9 71.2 7.9 1.36 50.9

D 7.3 2.6 83.4 14.0 2.33 1083


and 28.4% from soil A, B, C, and D2. Similarly, the extraction ef-

fi ciencies for pyrene of 20% ethyl lactate solution were 1.7 to 3.5

times more than those extracted with 20% ethanol solution.

For both PAHs the removal effi ciencies followed the order

of soil A > soil C > soil B > soil D2 for ethyl lactate as well

as ethanol. Th us, it decreased with increasing soil organic car-

bon content. Also various other studies have shown that soil

organic matter reduces the extractability of organic contami-

nants from soil (Chu and Kwan, 2003; Lee et al., 2004; Chu

et al., 2006). Chu and Kwan (2003) found that the extraction

of 4, 4’-dichlorobiphenyl from a contaminated soil by solvent/

surfactant-aided washing was inversely proportional to the soil

organic carbon content. In the case of surfactants this eff ect

may be explained by sorption of the surfactant to the organic

matter of a soil (Lee et al., 2004). As soils with a higher or-

ganic matter content will adsorb more surfactant than soils

with a lower organic matter content, a greater surfactant dose

is needed to obtain the same surfactant concentration in the

soil solution and thus the same dissolution eff ect. However, in

this study the concentration of ethyl lactate or ethanol did not

signifi cantly decrease in the solution during the washing pro-

cess (data not shown), indicating that the two cosolvents were

not signifi cantly adsorbed to the solid phase. Th is means that

the organic matter eff ect on PAH removal cannot be explained

by sorption of the cosolvents in this case. Kan et al. (1998)

proposed to partition organic chemicals in soil into two pools:

(i) a labile pool that can be readily and reversibly desorbed; and

(ii) an irreversible pool, resulting from covalent binding to soil

organic matter. Organic pollutants such as PAHs have a high

binding affi nity to organic matter and thus binding increases

Fig. 1. Solubility of phenanthrene and pyrene after 24-h equilibration in aqueous solution at diff erent concentrations of ethyl lactate or ethanol as organic cosolvent. Error bars represent standard errors. At some point they are not visible because they are smaller than the symbols used for the data points.

Fig. 2. Effi ciency of (A, B) phenanthrene and (C, D) pyrene removal from spiked soils as a function of cosolvent (A and C: ethyl lactate, B and D: ethanol) concentration in aqueous solution. Error bars represent standard errors. At some point they are not visible because they are smaller than the symbols used for the data points.


with the soil organic matter content, which in turn decreases

the removal effi ciency.

Extraction of Copper from SoilFigure 3 shows that EDDS has a strong capacity to extract

Cu from the soil. Above a molar EDDS/Cu ratio of 1 the ex-

traction rate of Cu increased only slightly with a further in-

crease in the EDDS/Cu molar ratio. Ethyl lactate alone without

EDDS did not increase Cu removal. Less than 2% of the Cu

was extracted from the soil even at an ethyl lactate concentra-

tion of 20% (data not shown). Th e extraction of Cu by EDDS

can be explained by the formation of Cu-EDDS complexes. It

is expected that the extractability increases with the stability

constant of metal-ligand complexes. Th e EDDS and EDTA

form Cu-complexes of nearly equal strength, with logarithms

of the stability constants >18 (Martell et al., 2001). However,

EDDS is preferred in soil washing applications because in con-

trast to EDTA it is readily biodegradable in the environment

(Van Devivere et al., 2001; Grčman et al., 2003; Tandy et al.,

2004). Tandy et al. (2004) reported that up to 67% of the

Cu in a contaminated soil was extracted by a washing solution

with EDDS. Th e relatively low extraction effi ciency (<37%) in

this study is probably due to an elevated content in Cu-bearing

ore minerals in the mine soil. Th e sequential extraction results

given below support this view.

Simultaneous Extraction of Copper and Polycyclic

Aromatic Hydrocarbons from SoilFigure 4 shows that ethyl lactate and EDDS mixtures can

effi ciently extract PAHs and Cu from soil. Th e removal effi -

ciencies for phenanthrene were higher than those for pyrene,

and they increased with the percentage of ethyl lactate in the

solution. For the EDDS solution containing 20% ethyl lac-

tate, the removal effi ciencies were 69.7% for phenanthrene and

39.9% for pyrene. Th e presence of EDDS and Cu did not sig-

nifi cantly alter the removal effi ciencies for phenanthrene and

pyrene (compare with Fig. 2). Th is agrees with the fi nding that

EDDS and EDDS-Cu had little impact on PAH solubilization

in ethyl lactate (data not shown).

In absence of ethyl lactate the extraction effi ciency of

EDDS for Cu was about 34.8% (Fig. 3 and 4). Addition of

ethyl lactate increased this effi ciency to more than 40% (Fig.

4). Th e removal rate showed little dependence on the rate of

ethyl lactate application within the range of applied concentra-

tions (0.5–20%). Th e logarithmic EDDS/Cu stability constant

(logKs) was found to be approximately 19 using potentiometer

titration. Addition of ethyl lactate increased the logarithmic

stability constant to 26 at low concentrations (i.e., 10 mg L–1)

and further with increasing ethyl lactate concentration up to

30 mg L–1. Such a vast increase in stability constant provides a

plausible explanation for the increased Cu removal in presence

of ethyl lactate. Fan et al. (2001) found that the presence of

a cosolvent such as methanol (MeOH), ethanol (EtOH), di-

methylsulfoxide (DMSO), N, N-dimethylformamide (DMF),

or 1,4-dioxane (DOX) increased the stability constant of Cu-

glycine in aqueous solution. As solvent molecules compete

with ligands for binding with cations, solvents can infl uence

the binding strength of a ligand. Water, a solvent of high polar-

ity, can strongly compete with ligands for Cu. Th erefore, it is

reasonable to expect an increase in the stability constants on

addition of a cosolvent such as ethyl lactate, whose polarity is

lower than that of water, to an aqueous Cu/ligand solution (Fan

et al., 2001). It can be assumed that ethyl lactate reduced the

overall polarity of the aqueous solutions in our experiments,

weakening the affi nity of the water molecules to Cu and thus

facilitating binding between EDDS and Cu.

Copper Fractionation in Soil D before and after ExtractionIn general, the total concentration of a pollutant in soil is

not a good measure of its bioavailability and therefore is not a

Fig. 3. Removal of Cu from soil D1 by EDDS applications at diff erent molar EDDS/Cu ratios. Error bars represent standard errors. At some points they are not visible because they are smaller than the symbols used for the data points.

Fig. 4. Extraction of Cu, phenanthrene and pyrene from soil D2 by mixed EDDS/ethyl lactate solutions at a EDDS/Cu ratio of 2 and diff erent concentrations of ethyl lactate. Error bars represent standard errors. At some points they are not visible because they are smaller than the symbols used for the data points.


suitable indicator for assessing the environmental risks of soil

contamination (Peijnenburg et al., 1997). Th e bioavailability

of heavy metals is more closely correlated to easily extractable

pools. Metal fractionation by extractability could therefore

form a better basis for evaluating remediation performance

than total concentration (Mulligan et al., 2001a). Figure 5

shows the fractionation of Cu in soil D before and after pollut-

ant extraction was performed using EDDS/ethyl lactate.

In this soil Cu was found mainly in the residual (36.2%)

and the oxidizable (31.7%), and much less in the reducible

(11.5%), and the acid extractable (20.6%) fraction. It is known

that EDDS readily extracts metal from the acid extractable, and

partially also from the reducible and the oxidizable fractions,

but has little eff ect on the residual fraction (Cao et al., 2008).

Th us, the large residual fraction of our soils explains the rela-

tively low extraction effi ciency (~34.8%, molar ratio of EDDS/

Cu = 2). In fact, extraction by EDDS alone primarily reduced

the acid extractable, the reducible, and the oxidizable fraction,

while there was little or no eff ect on the residual fraction in this

study. Addition of ethyl lactate to the EDDS solution further

enhanced the extraction of Cu, mainly from the acid extract-

able, the reducible, and also from the residual, but surprisingly

not from the oxidizable fraction. Further studies are needed to

clarify this point. Compared to the magnitude of these frac-

tions in the untreated soil, the four fractions were reduced by

73.2% (acid extractable fraction), 77.6% (reducible fraction),

36.5% (oxidizable fraction), and 20.2% (residual fraction). In

total, the ethyl lactate/EDDS mixture removed 42.9% of the

resident Cu from soil D2, of which more than 80% derived

from the acid extractable, reducible and oxidizable fractions.

Th is indicates that although extraction effi ciency with ethyl

lactate-modifi ed EDDS solution is relatively low (~43%), it

can substantially reduce the bioavailability of soil-contaminat-

ing Cu to plants and humans, and thus also the toxicity risks to

the environmental quality and human health.

ConclusionsAlthough the PAHs were spiked and thus the rates for their

removal obtained here will not be representative for fi eld-con-

taminated soils, the results of this study, show that aqueous

solutions of ethyl lactate and EDDS can be effi ciently used to

simultaneously remove organic contaminants and heavy metals

from contaminated soils. Th e required concentration of cosol-

vent was found to increase with the organic matter content of

the soil. Ethyl lactate can signifi cantly enhance the effi ciency

EDDS in extracting Cu.

AcknowledgmentsTh is work was supported by the National Natural Science

Foundation of China (20407012), National Natural Science

Foundation of Jiangsu Province (BK2007523), the National High

Technology Research and Development Program(“863”Program)

of China (2007AA06Z307), and the National Science Foundation

for Distinguished Youth Scholar (40725010).

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