By Sunflower Oil

Chemosphere 58 (2005) 291–298 www.elsevier.com/locate/chemosphere

Dissolution and removal of PAHs from a contaminated soil using sunflower oil Zongqiang Gong a

a,b

, Kassem Alef c, B.-M. Wilke

c,* ,

Peijun Li

a

Institute of Applied Ecology, Chinese Academy of Sciences, P.O. Box 417, Shenyang 110016, PR China b Graduate School of Chinese Academy of Sciences, Beijing 100039, PR China c Institute of Ecology, Technical University Berlin, Franklinstrasse 29, D-10587 Berlin, Germany Received 28 August 2003; received in revised form 25 June 2004; accepted 13 July 2004

Abstract This study reports on the feasibility of remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soils using sunflower oil, an environmentally-friendly solvent. Batch experiments were performed to test the influence of oil/ soil ratio on the remediation of PAH contaminated soil, and to test the mass transfer behaviors of PAHs from soil to oil. An empirical model was employed to describe the kinetics of PAH dissolution and to predict equilibrium concentrations of PAHs in oil. PAH containing oil was regenerated using active carbon. Results show that dissolution of PAHs from a Manufactured Gas Plant (MGP) soil at oil/soil ratios of one or two were almost the same. Nearly all PAHs (81–100%) could be removed by sunflower oil dissolution. Mass transfer coefficients for low molecular PAHs namely fluoranthene, phenanthrene and anthracene were one or two orders of magnitude higher than those for high molecular PAHs with 4–6 rings. Ninety milliliters of PAH containing oil could be regenerated by 10 g active carbon in a batch reactor. Such a remediation procedure indicates that sunflower oil is a promising agent for the removal of PAHs from MGP soils. However, further research is required before the method can be used for in situ remediation of contaminated sites. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Polycyclic aromatic hydrocarbons; Soil remediation; Vegetable oil; Mass transfer; Equilibrium partitioning

1. Introduction Many laboratory and field studies have been carried out to date to achieve the cost-effective remediation of hydrophobic organic contaminants (HOCs) in soils

* Corresponding author. Tel.: +49 30314 71193; fax: +49 30314 71431. E-mail address: [email protected] (B.-M. Wilke).

and sediments. Bioremediation by the use of living organisms, has been applied for the removal of organic contaminants, such as PCBs, PAHs, BTEX, TNT from soil (Wang et al., 1990; Macdonald and Rittmann, 1993; Bradley and Chapelle, 1995; Pagano et al., 1995; Tiehm et al., 1997; Daun et al., 1998; Bruns-Nagel et al., 1998; Rockne and Strand, 1998). Unfortunately, even though bioremediation is one of the most costeffective technologies, removals of HOCs, especially PAHs and PCBs with high molecular weights, were not efficient as expected (May et al., 1997; Cornelissen

0045-6535/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2004.07.035

292

Z. Gong et al. / Chemosphere 58 (2005) 291–298

et al., 1998). This was mainly due to their extremely low solubility and slow desorption into the aqueous phase. In recent years, many researchers have proposed some novel remediation measures to clean HOC contaminated soils. The use of surfactants has been applied successfully for removal of soil-bound HOCs (West and Harwell, 1992; Yeom et al., 1996). Because of political and environmental reasons the use of surfactants and other chemical solvents has been prohibited in some countries (Dadkhah and Akgerman, 2002). Supercritical fluid extraction (SFE) is also a technology that has been widely explored when cleaning organic contaminated soils. CO2 and water appear to be the most common fluids used for SFE (Schleussinger et al., 1996; Lagadec et al., 2000). However, SFE necessitates very special materials of construction in addition to the cost of high temperatures and pressures and cannot be used in situ. With the aforesaid problems in mind, we are trying to find an environmentally-friendly solvent, which has additional advantages of being readily available, nontoxic and low in cost for the efficient in situ remediation of Manufactured Gas Plant (MGP) sites heavily contaminated with polycyclic aromatic hydrocarbons (PAHs). MGPs produced gas by cracking oil or coal and by releasing light hydrocarbons that were used for lighting and household needs. MGP sites exist commonly in many countries. At MGPs that use coal, the primary residual carbon was pyrolyzed coal particles. At MGPs that use oil, a finer organic carbon residue similar to lampblack soot was produced. In both cases, the primary organic pollutants of concern are PAHs (Hawthorne et al., 2002). Residual PAHs-containing material, either mixed in soils or sediments or occurring as a discrete phase, can also lead to the long-term desorption and dissolution of PAHs into groundwater (Haeseler et al., 1999). A number of chemical solvents have been explored to extract PAHs from contaminated soil aiming for soil remediation rather than analysis (Khodadoust et al., 2000; Rababah and Matsuzawa, 2002). The advantages of using vegetable oil as nontoxic, inexpensive, and effective solvent for extraction of polychlorinated dibenzo-p-dioxins and dibenzofurans have been reported by Isosaari et al. (2001). The safety of field applications was also demonstrated in their report. To our knowledge, the possibility of using vegetable oil to remove PAHs from weathered MGP soils has not been investigated yet. The objectives of this study were: (a) to determine dissolution of individual PAHs from a weathered MGP soil by the use of sunflower oil; (b) to investigate the effects of PAH molecular weight and contact time on the transport and removal rates of PAHs; (c) to test the influence of oil/soil ratio on the removals of PAHs from soil; (d) to regenerate PAH containing oil for recycling purpose using activated carbon.

2. Materials and methods 2.1. Soil sample A sandy soil (95.6% sand, 0.6% silt, 3.8% clay) was collected from a former MGP site historically contaminated with PAHs. It was sieved to <2 mm to break soil clumps and to remove rocks and was then mechanically mixed to ensure homogeneity. The field moist soil was stored at 4 °C for further experiments. The soil had a pH of 6.6 (measured in 0.01 M CaCl2) and an organic carbon content of 4.6%. It contained 5450 mg PAH kg
1 soil. Concentrations of individual PAHs are given in Table 1. Homogeneity of the soil was verified by parallel extraction. With exception of naphthalene standard deviations of PAH concentrations in the soil varied between 2% and 11% (Table 1). 2.2. Solubilization of soil-bound PAHs using sunflower oil Extraction of PAHs from the MGP soil using sunflower oil was investigated in batch experiments. In our preliminary experiments we tested three different oils, i.e., sunflower oil, rape oil and soybean oil. Results showed that the three oils had the same extraction efficiency (Alef et al., 2003a). Sunflower oil was chosen for further investigation because it was the cheapest one. To test mass transfer rates of PAHs from soil to sunflower oil, 150 ml sunflower oil was poured into a glass bottle, which contained 150 or 75 g MGP soil. The bottles were sealed and mechanically shaken at 200 rpm on an orbital shaker. After 5, 15, 50 min and 1, 3, 7 d, the soil suspensions were settled for 5 min and an aliquot of oil sample was withdrawn into a 4ml vial for future analysis. 2.3. Modeling the dissolution kinetics of PAHs from MGP soil In order to describe the kinetics of PAHs dissolution, an empirical first order model was employed. This model can be used when dissolution (or desorption) arises out of equilibrium partitioning and mass transfer phenomena take place between two phases, one of which is a liquid phase and the other is a solid phase. The theoretical basis of this model is that at equilibrium, there is no net transfer between two phases and partition coefficients can be used to represent the ratio of the concentration of the same chemical species in two phases. Relative concentrations of PAHs between two distinct phases provide an explicit measure of the propensity of PAHs to exist in each phase. In this study, the kinetics of PAH dissolution and equilibrium was plotted, and mass transfer theory was used to derive first-order mass transfer coefficients and equilibrium oil phase concentration by fitting the data to

Z. Gong et al. / Chemosphere 58 (2005) 291–298

293

Table 1 PAH concentrations in the MGP soil PAHs

Water solubility (mg/l)a

log Kowa

Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benz(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(a)pyrene Dibenz(ah)anthracene Benzo(ghi)perylene Indenopyrene Sum of PAHs

30 3.47 3.93 1.98 1.29 0.07 0.26 0.14 0.014 0.002 0.0012 0.0006 0.0038 0.0005 0.00026 0.062

3.37 4.33 4.07 4.18 4.46 4.45 5.33 5.32 5.61 5.61 6.57 6.84 6.04 6.5 7.1 7.66

a

PAH in soil Conc (mg/kg)

Sd (%)

5.7 175.8 550.4 291.7 1111.6 147.1 519.8 1312.4 278.4 239.1 117.3 72.2 301.9 51.9 200 77.8 5453.2

101.8 2.7 3.7 2.9 6.7 4.1 6.8 2.8 6.7 2.6 5.1 6.9 2.4 8.5 10.8 10.4

According to Tiehm et al. (1997) and Sim and Overcash (1983).

C 0 ¼ C e ½1
expð
ktÞ where C0 is the PAH concentration of the oil phase at time t, k is the lumped mass transfer coefficient, Ce is the equilibrium oil-phase concentration and t is the contact time with oil (Woolgar and Jones, 1999). Fitting of the data to the equation was achieved using a nonlinear curve fitting of software Sigma. 2.4. Feasibility of sunflower oil regeneration The feasibility of oil regeneration was investigated using activated carbon to adsorb PAHs from used oil by means of batch experiment in an Erlenmeyer flask (250 ml nominal volume). A total of 90 ml used oil was poured into a 250-ml Erlenmeyer flask, to which 10 or 20 g activated carbon was added, a flask without activated carbon served as a control. The Erlenmeyer flasks were placed upright on the flat bed orbital shaker rotating at 150 rpm for 24 h. The suspensions were settled and oil samples were taken and filtered through glass membrane for PAH analysis. 2.5. Methods for analyses of contaminated soil and oil samples PAHs in soil samples were extracted by a mechanical chemical extraction procedure proposed by VDLUFA. The method was most suitable for extraction of PAHs from highly contaminated soils (Song et al., 2002). Recovery rates varied between 43.1% for Naphthalene and 95% for Benzo(k)fluoranthene. Fifteen grams sodium chloride, 100 ml deionized water, 200 ml acetone and 150 ml dichloromethane were added to 10 g soil in

a glass bottle. The bottle was sealed with Teflon screw cover, placed on the orbital shaker and shaken at 200 rpm over 16 h. After the separation of organic and water phases, an aliquot of organic phase was cleaned in a chromatography column filled with 3 g deactivated aluminum oxide (deactivated by 15% water addition) and 5 g activated silica gel (70–230 mesh, activated by oven-heating at 130 °C for 16 h and cooled in a desiccator at least for 10 min before use) and 4 spoons of anhydrous sodium sulphate. The chromatography column was eluted with 100 ml 4:1 hexane:dichloromethane (v:v). The eluate was concentrated by rotary evaporator and dried by a stream of nitrogen gas and finally dissolved in acetonitrile for HPLC analysis. The oil sample was dissolved in petroleum ether and cleaned up in a chromatography column filled with 10 g activated silica gel (activated under the same conditions as described above), and 4 spoons of anhydrous sodium sulphate. The chromatography column was eluted with 100 ml 2:1 toluene:petroleum ether (v:v). An aliquot of elution was taken and was then dried by nitrogen gas, and finally dissolved in acetonitrile for HPLC analysis. The procedure was described by Alef et al. (2003b). Recovery rates varied between 82.5% for Napththalene and 105.6% for Fluoranthene. Standard deviations of three replicates were 3.5 mg kg
1 at a total concentration of 2925 mg kg
1. 2.6. HPLC analysis PAH analysis was performed with an HPLC equipped with a gradient pump (KNAUER K1001), an autosampler (TSP AS100), and a reverse-phase

294

Z. Gong et al. / Chemosphere 58 (2005) 291–298

C-18 column. Acenaphthylene and indenopyrene were quantified by UV detector, while the rest of the 14 PAHs were measured by fluorescence detector (TSP FL2000) at specific excitation/emission wavelength. Elution conditions were as follows: for the first 5 min, a 1:1 (v:v) mixture of water and acetonitrile was used as the solvent at a flow rate of 0.4 ml/min throughout. During the next 15 min, acetonitrile in the mixture was linearly increased to 100% and maintained at that composition for 15 min. Thereafter, the solvent composition was returned to initial conditions within the next 2.5 min. In all cases, 8 ll of sample was injected to the HPLC by the autosampler. The concentrations of PAHs were calculated using HPLC software CHEM EURO 2000. An external standard 1647d SRM NBS mixture was used for quantification of 16 PAHs.

3. Results 3.1. Kinetics of PAH dissolution Kinetics of PAH dissolution from soil are shown by plotting the concentrations of PAHs released from the MGP soil vs. extraction time (Fig. 1). Results for naphthalene, acenaphthylene, and acenaphthene are not given because the reproducibility was very poor owing to their high volatility. Results of benzo(b)fluoranthene and benzo(k)fluoranthene were combined into one plot for their similar structures and figure lay out. During the initial phase (0–24 h), solubilization was rapid, which was followed by a phase of slower dissolution. For the PAHs with three rings, namely fluoranthene, phenanthrene and anthracene, an equilibrium could be approached within 24 h; for the PAHs with 4–6 rings an equilibrium was achieved after 72 h. The empirical model proposed by Woolgar and Jones (1999) is suitable to describe the kinetics of PAH dissolution in sunflower oil. The correlation coefficients of individual PAHs are highly significant and varied between 0.91 and 1 (Table 2). Using this model, we were able to obtain equilibrium PAH concentrations (Ce) and mass transfer coefficients (k). Transfer coefficients for 3-ring PAHs are nearly one or two orders magnitude higher than those of 4- to 6-ring PAHs, showing that a close to equilibrium situation will be approached first for 3-ring PAHs, then for 4- to 6-ring PAHs. Calculated k-values for the oil/soil ratio of 2:1 are lower than those for 1:1. Less amount of soil in batch reactor at an oil/soil ratio of 1:1 would provide more contact sites between the oil and the soil and thus resulted in relatively higher k-values in the initial phase of dissolution. The reason for the higher k-values at 1:1 ratio was also probably due to the better ‘‘grinding’’ effect between soil particles. In Fig. 2 we compared the extraction efficiency (in terms of PAH removal) using sunflower oil with that

using an organic solvent (e.g., acetone, dichloromethane) for the MGP soil. It can be seen that sunflower oil at both oil/soil ratios was as effective as organic solvent in removing PAHs from the MGP soil. No matter what size the PAH molecules were, their removal rates were similar, which was an advantage of using sunflower oil if compared with other methodologies that often have difficulties in removing high molecular weight PAHs. With respect to the cost of remediation we suggest that the oil/soil ratio of 1:1 should be sufficient even for highly contaminated soil. 3.2. Regeneration of sunflower oil Regeneration of sunflower oil is a vital step for the successful development of remediation process with sunflower oil as a solvent. Activated carbon was considered as a sorbent for the application in batch experiment. The overall efficiency of sorption process to achieve sunflower oil regeneration was determined based on concentrations of PAHs in oil before and after the activated carbon treatment. The remaining percentages of PAHs in the oil after a sorption process using 10 or 20 g activated carbon are shown in Fig. 3. For the majority of PAHs, more than 90% was removed by 20 g activated carbon. When the amount of activated carbon was reduced to 10 g, PAH removal dropped to a lower level, however, the regeneration result was still satisfactory. The control (without activated carbon) showed slight variation from the untreated sunflower oil containing PAHs, mostly by less than 10%. These results indicate that activated carbon is a good matrix to remove PAHs from sunflower oil. However, further investigation is required to optimize the regeneration process.

4. Discussion Transport and mass transfers of PAHs from the contaminated soil might be key processes responsible for reducing PAHs of the soil. To achieve maximum PAH removal, a specific period of time is required. Many studies on liquid agent remediation of organics contaminated soils tried to reduce the time required for the process (Bjo¨rklund et al., 1999; Lagadec et al., 2000; Reid et al., 2000). Also some comparisons were made between bioremediation and liquid extraction techniques (Hawthorne and Grabanski, 2000). Our results demonstrate a rapid dissolution of PAH contaminated soil within 1–3 days. In our experiments, proper mixing of the oil and soil should not be neglected, which was also suggested by Isosaari et al. (2001). It should also be noted that after dissolution of PAHs from contaminated soil, the sunflower oil turned dark brown in color, apparently containing a large amount of co-extracted soil organic materials. In the soils with organic content

Z. Gong et al. / Chemosphere 58 (2005) 291–298 300 250 200 150 100 50 0

Fluorene 0

Concentration in oil (mg.l-1)

1400 1200 1000 800 600 400 200 0

500 400 300 200 100 0

50

100

300 250 200 150 100 50 0

50

100

0

150

150

70 60 50 40 30 20 10 0

50

100

70 60 50 40 30 20 10 0

50

100

150

100

160 140 120 100 80 60 40 20 0

150

Anthracene 0

350 300 250 200 150 100 50 0 150

50

100

150

Benz(a)anthracene 0

50

100

150

400 300 200 100 Benzo(b+k)fluoranthene 50

250 200 150 100 50 0

Dibenz(ah)anthracene 0

50

0

150

100

Pyrene 0

Chrysene 0

50

1400 1200 1000 800 600 400 200 0

Fluoranthene 0

Phenanthrene

295

100

Benzo(a)pyrene

0

150

0

50

100

150

80 60 40 20 0

Benzo(ghi)perylene 0

50

100

Indenopyrene 0

150

50

100

150

Time hours

Fig. 1. Dissolution kinetics of PAHs using a first-order model (see Section 2). Experimental dissolution rates and model fitted curves of PAHs from the MGP soil. The dark circles denote the experimental data for oil/soil ratio of 1:1, the circles denote for oil/soil ratio of 2:1. The solid lines are the model fitting curves for oil/soil ratio of 1:1, whereas the dashed lines are for oil/soil ratio of 2:1.

Table 2 Oil phase equilibrium concentrations of PAHs (Ce) and mass transfer coefficients (k) derived by data fitting using a first-order model (see Section 2) Oil/soil ratio

1:1

PAHs

Ce

k

R2

2:1 Ce

k

R2

Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benz(a)anthracene Chrysene Benzo(b+k)fluoranthene Benzo(a)pyrene Dibenz(ah)anthracene Benzo(ghi)perylene Indenopyrene

230 ± 18 1125 ± 52 145 ± 11 440 ± 27 1251 ± 67 318 ± 1 256 ± 12 192 ± 8 368 ± 12 58 ± 2 226 ± 6 68 ± 2

1.91 ± 0.62 0.68 ± 0.16 0.94 ± 0.31 0.05 ± 0.01 0.09 ± 0.03 0.13 ± 0.03 0.06 ± 0.01 0.05 ± 0.01 0.06 ± 0.01 0.07 ± 0.01 0.06 ± 0.01 0.05 ± 0.01

0.91 0.97 0.92 0.98 0.98 1 0.99 0.99 0.99 0.99 1 0.99

138 ± 5 606 ± 17 76 ± 4 232 ± 18 630 ± 36 128 ± 6 113 ± 10 92 ± 3 160 ± 5 32 ± 2 105 ± 5 30 ± 2

1.03 ± 0.17 0.52 ± 0.08 0.80 ± 0.19 0.05 ± 0.02 0.05 ± 0.01 0.08 ± 0.02 0.03 ± 0.01 0.04 ± 0.01 0.05 ± 0.01 0.03 ± 0.01 0.05 ± 0.01 0.03 ± 0.01

0.98 0.99 0.97 0.96 0.98 0.99 0.96 0.99 0.99 0.99 0.99 0.98

296

Z. Gong et al. / Chemosphere 58 (2005) 291–298 1400

PAH removal (mg•kg-1)

1200 PAH concentration in soil 1000

oil/soil ratio of 1:1 oil/soil ratio of 2:1

800 600 400 200

Fl uo re ne Ph en an th re A ne nt hr ac en Fl uo e ra nt he ne Be Py nz re (a ne )a nt hr ac e Be Ch ne nz o( r y b) se flu ne Be or nz a o( nt k) he flu ne or a nt Be he nz D ne o( ib a) en py z( re a,h ne )a Be nt hr nz ac o( en gh e i)p er y le In ne de no py re ne

0

Fig. 2. Comparison of PAH removals at oil/soil ratios of 1:1 and 2:1.

PAH remaining in oil (%)

140 120 100 80 60 40 20

py r

en

e

e

e er

In

de

no

i)p gh

Be

nz

o(

ah z( en

D

ib

yl

ac hr

nt )a

o( nz

en

en

e

e a)

py r

en

en

e th

en

an Be

k)

flu

or

an or

flu Be

nz

o(

b) Be

nz

o(

nz Be

th

ne

e

se ry

(a

Fl

)a

nt

Ch

hr

ac

re

en

ne

ne nt

ra uo

Py

he

en

e

ne

ac

re

hr

th an

nt A

en Ph

Fl

uo

re

ne

0

Control Treated with 20 g activated carbon Treated with 10 g activated carbon

Fig. 3. Regeneration of PAH containing oil using activated carbon.

>0.1%, hydrophobic organic pollutant partitioning into the soil organic material has been found to be the dominant process (Magleod and Semple, 2000). Dissolution of soil organic materials into sunflower oil will also result in the soil organic material bound PAHs being dissolved into sunflower oil, which further enhances the capacity of sunflower oil to extract PAHs from the contaminated soil. Environmental behaviors of PAHs on historically contaminated soils are complicated by the fact that physicochemical properties of PAHs vary greatly. For example, the PAHs commonly associated with MGP sites range from two rings (naphthalene) to six rings (indenopyrene), with associated water solubility ranging

from 30 to 0.00026 mg/l, and octanol–water coefficient partition ranging from 3.37 to 7.66, respectively (Table 1). Given the wide range of PAH characteristics, the analogous removal rates of PAHs can be ascribed to the good capacity of sunflower oil to extract PAHs from soil, thus, the influence of physicochemical characteristics became less significant. It was demonstrated that the extractability of PAHs from soil decreased with prolonged aging of contamination (West and Harwell, 1992). The soil used in this study was collected from a former MGP site in Berlin, which had a decade-long history of contamination. Thus, our method exhibits promising rates and extents of PAH removal from aged soils.

Z. Gong et al. / Chemosphere 58 (2005) 291–298

The contamination at former gas plants is extremely severe, therefore, land use other than industrial purposes in these areas are always banned by the government or impossible, and the quality of ground water near the contaminated site is also threatened by PAH contaminants. The clean-up of heavily contaminated site using sunflower oil can release the problems related to PAHs. It is summarized in literature that major constituents of vegetable oil are oleic acid, simple phenols and phenolic acids, dicarboxylic acid, these acids are readily biodegradable. The degradability of remaining oil in soil was investigated in a series of soil respiration experiments. Our preliminary results (not shown) indicate that remaining oil in soil can be removed by conventional method, such as compost. The soil quality was remarkably improved after clean-up by sunflower oil as far as ecological risk assessment was concerned. Although the humic content and pore system of the soil were sacrificed, these two factors are less important for a nonagricultural purpose. Costs play an essential role in the applicability of remediation techniques. At this moment it is impossible to give an accurate and reliable cost estimation based only on our batch experiments. However, our results suggest that it is worthwhile to scale up the experiment to further test this technology for in situ remediation of PAH contaminated soil. A reliable estimate would be available after a semi field experiment on a pilot plant scale is completed.

5. Conclusions The present study demonstrates a novel soil remediation method that uses sunflower oil to extract PAHs from the contaminated soil. Results showed that sunflower oil had a good capability to extract PAHs from soil, especially the MGP soil containing extremely high concentrations of PAHs, which were difficult to remediate by other methodologies. Nearly 100% of PAHs were removed in batch experiments. Kinetics of PAH dissolution showed that equilibrium could be achieved within 24 h for 3-ring PAHs, and that after 3 d, mass transfers will be in an equilibrium condition for all the PAHs. Oil/ soil ratio did not have a significant influence on the removal rates of PAHs in batch experiments. By fitting the data to an empirical first-order model we derived equilibrium concentrations of PAHs in oil and mass transfer coefficients. These two parameters were quite meaningful for the determination of effects of PAH molecular weight, oil/soil ratio, and contact time on the efficiency of PAH removals. The PAH containing oil could be regenerated by adsorption of PAHs from sunflower oil using activated carbon. Before this technique is applied to in situ or ex situ remediation on a full scale, a thorough assessment should be made involving

297

costs and ecological risks related to the quality of sunflower oil, disposal of oil and activated carbon, the transport of soil, refill of contaminated site, and so on.

Acknowledgments This work was partially supported by a grant from National Science Foundation of China (20277040) to P.L., and a scholarship from BMBF of Germany (CHN 093) to Z.G. We thank Dr. P. Isosaari for his constructive advice on manuscript revision, Dr. P. Gong for editing the manuscript.

References Alef, K., Kapitzki, L., Gong, Z., Song, Y., Wilke, B.-M., Niebelschu¨tz, H., 2003a. Grundlagen zur Entwicklung eines Verfahrens zu in situ-Sanierung von Polyzyklischen Aromatischen Kohlenwasserstoffen (PAK) in Bo¨den mit Pflanzeno¨l. altlasten spektrum 2, S74–S79. Alef, K., Kapitzki, L., Fuchs, M., Wilke, B.-M., Stegmann, R., Niebelschu¨tz, H., 2003b. Bestimmung von Polzyklischen Aromatischen Kohlenwasserstoffen (PAK) in Boden/ Pflanzeno¨lextrakten. altlasten spektrum 1, 35–39. Bjo¨rklund, E., Bøwadt, S., Mathiasson, L., Hawthorne, S.B., 1999. Determining PCB sorption/desorption behavior on sediments using selective supercritical fluid extraction. 1. Desorption from historically contaminated samples. Environ. Sci. Technol. 33, 2193–2203. Bradley, P.M., Chapelle, F.H., 1995. Factors affecting microbial 2,4,6-trinitrotoluene mineralization in contaminated soil. Environ. Sci. Technol. 29, 802–806. Bruns-Nagel, D., Drzyzga, O., Steinbach, K., Schmidt, T.C., Lo¨w, E.von, Gorontzy, T., Blotevogel, K.-H., Gemsa, D., 1998. Anaerobic/aerobic composting of 2,4,6-trinitrotoluene-contaminated soil in a reactor system. Environ. Sci. Technol. 32, 1676–1679. Cornelissen, G., Rigterink, H., Ferdinandy, M.M.A., Noort, P.C.M.van, 1998. Rapidly desorbing fractions of PAHs in contaminated sediments as a predictor of the extent of bioremediation. Environ. Sci. Technol. 32, 966–970. Dadkhah, A.A., Akgerman, A., 2002. Hot water extraction with in situ wet oxidation: PAHs removal from soil. J. Haz. Mater. B (93), 307–320. Daun, G., Lenke, H., Reuss, M., Knackmuss, H.-J., 1998. Biological treatment of TNT-contaminated soil. 1. Anaerobic cometabolic reduction and interaction of TNT and metabolites with soil components. Environ. Sci. Technol. 32, 1956–1963. Haeseler, F., Blanchet, D., Druelle, V., Werner, P., Vandecasteele, J.-P., 1999. Ecotoxicological assessment of soils of former manufactured gas plant sites: bioremediation potential and pollutant mobility. Environ. Sci. Technol. 33 (24), 4379–4384. Hawthorne, S.B., Grabanski, C.B., 2000. Correlating selective supercritical fluid extraction with bioremediation behavior of PAHs in a field treatment plot. Environ. Sci. Technol. 34, 4103–4110.

298

Z. Gong et al. / Chemosphere 58 (2005) 291–298

Hawthorne, S.B., Poppendieck, D.G., Grabanski, C.B., Loehr, C., 2002. Comparing PAH availability from manufactured gas plant soils and sediments with chemical and biological tests. 1. PAH release during water desorption and supercritical carbon dioxide extraction. Environ. Sci. Technol. 36, 4795–4803. Isosaari, P., Tuhkanen, T., Vartiainen, T., 2001. Use of olive oil for soil extraction and ultraviolet degradation of polychlorinated dibenzo-p-dioxins and dibenzofurans. Environ. Sci. Technol. 35, 1259–1265. Khodadoust, A.P., Bachi, R., Suidan, M.T., 2000. Removal of PAHs from highly contaminated soils found at prior manufacture gas operations. J. Haz. Mater. 80, 159–174. Lagadec, A.J.M., Miller, D.J., Lilke, A.V., Hawthorne, S.B., 2000. Pilot-scale subcritical water remediation of polycyclic aromatic hydrocarbon- and pesticide-contaminated Soil. Environ. Sci. Technol. 34, 1542–1548. Macdonald, J.A., Rittmann, B.E., 1993. Performance standards for in situ bioremediation. Environ. Sci. Technol. 27, 1974– 1979. Magleod, C.J.A., Semple, K.T., 2000. Influence of contact time on extractability and degradation of pyrene in soils. Environ. Sci. Technol. 34, 4952–4957. May, Robert, Schro¨der, P., Sandermann Jr., H., 1997. Ex situ process for treating PAH-contaminated soil with Phanerochaete chrysosporium. Environ. Sci. Technol. 31, 2626–2633. Pagano, J.J., Scrudato, R.J., Roberts, R.N., Bemis, J.C., 1995. Reductive dechlorination of PCB-contaminated sediments in an anaerobic bioreactor system. Environ. Sci. Technol. 29, 2584–2589. Rababah, A., Matsuzawa, S., 2002. Treatment system for solid matrix contaminated with fluoranthene. 1-Modified extraction technique. Chemosphere 46, 39–47.

Reid, B.J., Stokes, J.D., Jones, K.C., Semple, K.T., 2000. Nonexhaustive cyclodextrin-based extraction technique for the evaluation of PAH bioavailability. Environ. Sci. Technol. 34, 3174–3179. Rockne, K.J., Strand, S.E., 1998. Biodegradation of bicyclic and polycyclic aromatic hydrocarbons in anaerobic enrichments. Environ. Sci. Technol. 32, 3962–3967. Schleussinger, A., Ohlmeier, B., Reiss, I., Schulz, S., 1996. Moisture effects on the cleanup of PAH-contaminated soil with dense carbon dioxide. Environ. Sci. Technol. 30, 3199– 3204. Sim, R.C., Overcash, M.R., 1983. Fate of polynuclear aromatic compounds (PNAs) in soil–plant systems. Residue Rev. 88, 1–68. Song, Y.F., Jing, X., Fleischmann, S., Wilke, B.M., 2002. Comparative study of extraction methods for the determination of PAHs from contaminated soils and sediments. Chemosphere 48, 993–1001. Tiehm, A., Stieber, M., Werner, P., Frimmel, F.H., 1997. Surfactant-enhanced mobilization and biodegradation of polycyclic aromatic hydrocarbons in manufactured gas plant soil. Environ. Sci. Technol. 31, 2570–2576. Wang, X., Yu, X., Bartha, R., 1990. Effect of bioremediation on polycyclic aromatic hydrocarbon residues in soil. Environ. Sci. Technol. 24, 1086–1089. West, C.C., Harwell, J.H., 1992. Surfactants and subsurface remediation. Environ. Sci. Technol. 26, 2324–2330. Woolgar, P.J., Jones, K.C., 1999. Studies on the dissolution of polycyclic aromatic hydrocarbons from contaminated materials using a novel dialysis tubing experimental method. Environ. Sci. Technol. 33, 2118–2126. Yeom, I.T., Ghosh, M.M., Cox, C.D., 1996. Kinetic aspects of surfactant solubilization of soil-bound polycyclic aromatic hydrocarbons. Environ. Sci. Technol. 30 (5), 1589–1595.