Fenton And O3

Degradation of PAHs in Soils

Research Articles

Research Articles

Comparison of Fenton's Reagent and Ozone Oxidation of Polycyclic Aromatic Hydrocarbons in Aged Contaminated Soils Sofia Jonsson1*, Ylva Persson1, Sofia Frankki2, Staffan Lundstedt1,3, Bert van Bavel4, Peter Haglund1 and Mats Tysklind1 1 Environmental

Chemistry, Department of Chemistry, Umeå University, 901 87 Umeå, Sweden Department of Forest Ecology, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden 3 Present Address: Environmental Health Centre, Tunney's Pasture Ottawa, Ontario, K1A 0K9, Canada 4 Man-Technology- Environment Research Centre, Örebro University, 701 82 Örebro, Sweden 2

* Corresponding author ([email protected])

DOI: http://dx.doi.org/10.1065/jss2006.08.179 Abstract

Background. Polycyclic aromatic hydrocarbons (PAHs) are formed as a result of incomplete combustion and are among the most frequently occurring contaminants in soils and sediments. PAHs are of great environmental concern due to their ubiquitous nature and toxicological properties. Consequently, extensive research has been conducted into the development of methods to remediate soils contaminated with PAHs. Fenton's reagent or ozone is the most commonly studied chemical oxidation methods. However, the majority of remediation studies use soils that have been artificially contaminated with either one or a limited number of PAH compounds in the laboratory. Hence, it is essential to extend such studies to soils contaminated with multiple PAHs under field conditions. Objectives. The objective of this study is to investigate the capacity of Fenton's reagent and ozone to degrade PAHs in soils. The soils have been collected from a number of different industrial sites and, therefore, will have been exposed to different PAH compounds in varying concentrations over a range of time periods. The capacity of Fenton's reagent and ozone to degrade PAHs in industrially contaminated soils is compared to results obtained in studies using soils artificially contaminated with PAHs in the laboratory. Methods. Nine soil samples, contaminated with PAHs, were collected from five different industrial sites in Sweden. For the Fenton's reagent procedure, the pH of the soil slurry samples was adjusted to pH 3 and they were kept at a constant temperature of 70ºC whilst H2O2 was added. For the ozone procedure, soil samples were mixed with 50% water and 50% ethanol and kept at a constant temperature of 45ºC. Ozone was then continually introduced to each soil sample over a period of four hours. Following the Fenton's reagent and ozone oxidation procedures, the samples were filtered to isolate the solid phase, which was then extracted using pressurized liquid extraction (PLE). The sample extracts were cleaned up using open columns and then analysed by gas chromatography-mass spectrometry (GC-MS). Results. The relative abundance of the detected PAHs varied between soils, associated with different industries. For example, low molecular weight (LMW) PAHs were more abundant in soil samples collected from wood impregnation sites and high overall PAH degradation efficiencies were observed in soils originating from these sites. In the contaminated soils studied, PAHs were more effectively degraded using Fenton's reagent (PAH degradation efficiency of 40–86%) as opposed to ozone (PAH degradation efficiency of 10–70%). LMW PAHs were more efficiently degraded, using ozone as the oxidizing agent, whereas the use of Fenton's reagent resulted in a more even degradation pattern for PAHs with two through six fused aromatic rings.

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Discussion. The degradation efficiency for both methods was largely dependent on the initial PAH concentration in the soil sample, with higher degradation observed in highly polluted soils. LMW PAHs are more susceptible to degradation than high molecular weight (HMW) PAHs. As a result of this the relative abundance of large (often carcinogenic) PAHs increased after chemical oxidation treatment, particularly after ozone treatment. Repeated Fenton's reagent treatment did not result in any further degradation of soil PAHs, indicating that residual soil PAHs are strongly sorbed. The effectiveness of the two oxidation treatment approaches differed between industrial sites, thus highlighting the importance of further research into the influence of soil properties on the sorption capacity of PAHs. Conclusions. This study demonstrates that the degree to which chemical oxidation techniques can degrade soil bound PAHs chemical degradation is highly dependent on both the concentration of PAHs in the soils and the compounds present, i.e. the various PAH profiles. Therefore, similarities in the PAH degradation efficiencies in the nine soil samples studied were observed with the two chemical oxidation methods used. However, the degradation performance of Fenton's reagent and ozone differed between the two methods. Overall, Fenton's reagent achieved the highest total PAH degradation due to stronger oxidation conditions. LMW PAHs showed higher susceptibility to oxidation, whereas high molecular weight (HMW) PAHs appear to be strongly sorbed to the soils and therefore less chemically available for oxidation. This study highlights the importance of including soils collected from a range of contaminated sites in remediation studies. Such soil samples will contain PAH contaminants of varying concentrations, chemical and physical properties, and have been aged under field conditions. In addition to the chemical and physical properties of the soils, these factors will all influence the chemical availability of PAHs to oxidation. Recommendations and Perspectives. We recommend including aged contaminated soils in chemical degradation studies. In future chemical remediation work, we intend to investigate the potential influence of the chemical and physical properties of PAHs and soil parameters potential influence on the chemical oxidation efficiency in aged contaminated soils. Due to the vast number of contaminated sites there is a great need of efficient remediation methods throughout the world. This study shows the difficulties which may be experienced when applying remediation methods to a variation of contaminated sites. Keywords: Aged contaminated soils; chemical oxidation; coke production; degradation; Fenton's reaction; gas works; ozone oxidation; polycyclic aromatic hydrocarbons (PAHs); soil remediation; wood impregnation

J Soils Sediments 6 (4) 208 – 214 (2006) © 2006 ecomed publishers (Verlagsgruppe Hüthig Jehle Rehm GmbH), D-86899 Landsberg and Tokyo • Mumbai • Seoul • Melbourne • Paris

Research Articles

Degradation of PAHs in Soils

Introduction

Polycyclic aromatic hydrocarbons (PAHs), which consist of two or more fused benzene rings, comprise one of the most frequently occurring groups of organic contaminants in soils and sediments as a result of their extensive release into the environment. The physico-chemical properties of PAHs vary greatly. For example, high molecular weight (HMW) PAHs are more hydrophobic and have a greater affinity for soil organic matter than low molecular weight (LMW) PAHs. Sixteen PAHs, many of which are toxic, mutagenic, and carcinogenic, have been identified by the US Environmental Protection Agency (US-EPA) and the Swedish EPA as priority pollutants [1]. In addition, the Swedish EPA has issued recommended maximum residue levels of PAHs in soils after remediation treatment [2]. Degrading PAHs by chemical oxidation is one of several approaches adopted in the remediation of contaminated soil. Fenton's reagent (discovered in the 1890s by H.J.H. Fenton) and ozone treatment are two of the most frequently investigated chemical oxidation techniques [3,4]. These reagents form hydroxyl (OH) radicals, which are strong, non-specific, oxidizing agents. Chemical oxidation using Fenton's reagent is conducted under acidic conditions where OH radicals are formed by using hydrogen peroxide with Fe2+ as a catalyst. Chemical oxidation with ozone, introduced either in a gaseous or aqueous form, occurs when ozone decomposes to form OH radicals via a catalytic reaction at the reactive site on soils [3]. Ozone has been proposed as a promising in situ remediation technique [5–9], as has a modified Fenton's reaction in recent years (i.e. without the addition of Fe2+ or at neutral pH) [10–15]. Remediation of soils contaminated with PAHs via chemical oxidation is hampered by the fact that sorbed contaminants resist oxidative attack more effectively than contaminants in solution [12,15]. Sorbed contaminants are likely to remain unavailable to the chemical reactants that reside in the aqueous phase. In addition, the efficiency of oxidation also

decreases as the chemical oxidation process proceeds to oxidise the organic constituents of the soils. The period of time that has elapsed from when the soil was first contaminated with PAHs and when the soil is treated is also of great importance as the contaminants will diffuse further into the organic material of the soil over time. This process is often referred to as aging and often results in a reduced susceptibility of the contaminants to remediation processes [16]. The majority of soil remediation studies focus on bioremediation [17], and the susceptibility of PAHs to chemical oxidation is much less frequently investigated. Understanding of the underlying mechanism of the sequestration phenomenon of contaminants in soils is essential for the development of efficient and cost-effective chemical remediation methods. To date, the majority of chemical optimisation studies have been performed using soils that have been artificially contaminated with one or a limited number of individual PAHs in the laboratory. The degradation of a complex mixture of PAH compounds in soils that have been contaminated for many years is far more difficult [18,19]. In this study, nine soil samples have been collected for investigation from five different industrial sites in Sweden. By their very nature, the soils will have been contaminated with a complex mixture of PAHs at varying concentrations and over different periods of time. The soil samples from these sites have been subjected to Fenton's reagent and ozone treatments in order to investigate the techniques efficiency in degrading the various PAH compounds and whether the type and concentration of PAHs in the soils influences their susceptibility to degradation by oxidation. The capacity of Fenton's reagent and ozone to degrade PAHs in aged contaminated soils is compared to results obtained in studies using soils artificially contaminated with PAHs in the laboratory. 1

Materials and Methods

1.1

Soil sampling

Nine soil samples, each 5–10 kg in weight, were collected from five different industrial sites in Sweden (Table 1). The

Table 1: Sample site location, industry characteristics and soil types

Site

Location

1 (W)

Holmsund

Coordinates

N 63º 42m 00s E 20º 21m 00s 2 (W) Holmsund N 63º 42m 00s E 20º 21m 00s 3 (W) Holmsund N 63º 42m 00s E 20º 21m 00s 4 (C) Luleå N 65º 35m 00s E 22º 09m 00s 5 (W) Forsmo N 63º 16m 00s E 17º 12m 00s 6 (W) Forsmo N 63º 16m 00s E 17º 12m 00s 7 (W) Hässleholm N 65º 09m 00s E 13º 46m 00s 8 (W) Hässleholm N 65º 09m 00s E 13º 46m 00s 9 (G) Husarviken N 59º 21m 18s E 18º 06m 12s a Facility still in use, start unknown b Not known

J Soils Sediments 6 (4) 2006

Industry Wood preservation Wood preservation Wood preservation Coke production Wood preservation Wood preservation Wood preservation Wood preservation Gas work

Period of operation 1943–1983

Sampling depth 20–30 cm

Soil

Observations

Sandy Till

Black aggregated soil, strong smell of tar

1943–1983

10–20 cm

Sandy Till

Black aggregated soil, strong smell of tar

1943–1983

10–20 cm

Sandy Till

Smell of tar

a

Top soil

Sediment

1933–1950

2–18 cm

Fine sand

Black waterlogged sediment, oily film on water surface Black aggregated well sorted sandy soil

1933–1950

0–10 cm

Fine sand

Black aggregated well sorted sandy soil

1946–1965

40 cm

Smell of tar

1946–1965

40–60 cm

1893–1972

b

Coarse sand Coarse sand Sand

Smell of tar Smell of tar

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Degradation of PAHs in Soils soil samples were transported back to the laboratory in unused, solvent-washed steel containers. The industrial sites were carefully selected in order to obtain soil samples that would contain multiple PAH compounds at varying concentrations. The soil samples were air dried at room temperature, passed through a 2 mm sieve, and kept at constant temperature (4ºC) prior to analysis. In the tables and figures that follow, each soil sample has been assigned a code consisting of the sample number followed by a letter referring to the type of industry associated with the soil sample site (i.e. W for wood impregnation, C for coke production and G for gas works).

Research Articles at a constant temperature (45°C) and in suspension using a combined magnetic stirrer and heater. The ozone was generated from pure oxygen through electric discharges using an ozone generator (Anseros, Tübingen, Germany). Ozone was continuously pumped into the mixture at a rate of 25 mg per hour over a four hour period, with additional ethanol added to compensate for ethanol evaporation during the oxidation process. The amount of ozone produced was calculated by measuring the amount of oxygen used. The excess ozone that was not consumed by the slurry was passed through a catalyst and destroyed. 1.4

1.2

Chemicals

All solvents used were of analytical or glass distilled grade. Glassware was of high quality, machine washed with alkaline detergent and rinsed with solvent prior to usage. Hydrogen peroxide (30%) was purchased from J.T Baker (Deventer, Holland). FeSO4x7H2O (p.a), sulphuric acid (p.a,), silica gel 60 (0.063–0.20 mm), and sodium sulphate (p.a.) were from Merck (Darmstadt, Germany). The silica gel was activated at 130ºC for 24 hours and sodium sulphate at 550ºC for 48 hours. Silica gel was deactivated with 10% water (w/w) prior to use. Filter papers were purchased from Munktell (Grycksbo, Sweden), and internal standards (IS) and recovery standards (RS) were from Cambridge Isotope Laboratories (Andover, MA, USA). The IS consisted of 2[H ]naphthalene, 2[H ]acenaphthylene, 2[H ]acenaphthene, 8 8 10 2[H ]fluorene, 2[H ]anthracene, 2[H ]pyrene, 2[H ]benz10 10 10 12 [a]anthracene, 2[H12]benzo[k]fluoanthene, 2[H12]benzo[ghi]perylene and the RS consisted of 2[H10]fluoranthene. The compounds were quantified using a certified PAH reference standard mixture (SRM 2260, National Institute of Standards & Technology, Gaithersburg, MD, USA). 1.3

Soil treatment

Soil samples were subjected to chemical oxidation using both Fenton's reagent and ozone. Triplicate oxidation experiments were performed for all samples except for samples 2 and 3, which were only treated once. After treatment, all soil samples were filtered and air-dried at room temperature prior to further analysis. 1.3.1 Fenton's reagent procedure

The oxidation experiments were performed on slurries made up of 20 g of soil, 10 ml of 4 mM iron sulphate and 40 ml of hydrogen peroxide (30%) in 250 ml Erlenmeyer flasks, at a temperature of 70°C. 5% sulphuric acid was added to adjust the slurry to a pH of 3 prior to oxidation. The soil mixture was kept in suspension using a magnetic stirrer whilst 40 ml was added in increments (10 ml) within the first thirty min in order to avoid a violent reaction. The reaction was terminated after two hours with the addition of five drops of concentrated H2SO4 (pH < 1). 1.3.2 Ozone oxidation procedure

For the ozone oxidation procedure, 20 g of soil was mixed with 50 ml of 50% ethanol in water. The mixture was kept

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Extraction and sample clean-up

PAHs were extracted from the soil samples by pressurised liquid extraction (PLE) using a Dionex ASE200 (Sunnyvale, CA, USA) equipped with 11 ml stainless steel extraction cells. All extractions were performed at 14 MPa and a temperature of 150ºC with seven min of dynamic extraction, two static cycles of five min each, and with one cell volume used for rinsing with a purge time of sixty seconds. 1.4.1 Soil extraction

The PLE extraction cells were fitted with a cellulose filter to prevent clogging of the metal frit at the outlet of the cell. The cells contained 1 g of soil mixed with 5 g of anhydrous sodium sulphate, and were filled with anhydrous sodium sulphate. PLE was performed using n hexane:acetone (1:1, v/v) followed by methanol:acetic acid (99:1, v/v). 50 µL of IS was added to 10% portions of each extract and then evaporated to 1 ml and fractionated on open columns (15 mm in diameter, containing 5 g of silica and 1 g of anhydrous sodium sulphate). Each column was pre-rinsed with 20 ml n-hexane and eluted with 5 ml n hexane (waste fraction) followed by 15 ml n-hexane/dichloromethane (3:1, v/v). The second fractions were evaporated under a gentle stream of N2 and reconstituted in 1 ml of toluene. 1.4.2 Liquid-liquid extraction

The PAHs in the slurry filtrates were extracted by liquid-liquid extractions (1:1, v/v), performed in triplicate for each sample. The extraction solvents used were n-hexane and dichloromethane (for the Fenton's reagent and ozone treatments, respectively). The extracts were combined and evaporated under a gentle stream of N2 and reconstituted in 1 ml of n-hexane and fractionated as described above for soil extracts. 1.5

PAH determination

50 µL of RS was added to each sample; which were then transferred into 2 ml glass vials. The samples were analysed using a Fisons GC 8000 Top gas chromatograph (GC) with a 30 m (25 mm i.d.) DB-5 capillary column, film thickness 0.25 µM (J&W Scientific/Agilent Technologies, Folsom, CA, USA), coupled to an electron impact (EI) Fisons MD800 low resolution mass spectrometer (LR-MS). The sample aliquots (1 µL) were injected, split-less, into the GC. MS data were collected in full scan mode for identification and single ion monitoring (SIM) for quantification. Target com-

J Soils Sediments 6 (4) 2006

Research Articles

Degradation of PAHs in Soils

Table 2: All Polycyclic aromatic hydrocarbon species analyzed in the soils of this study

2 Aromatic Rings

3 Aromatic Rings

4 Aromatic Rings

5 Aromatic Rings

6 Aromatic Rings

Phenanthrene

Pyrene

Benzo(e)pyrene

Benzo(g,h,i)perylene

1-Methylphenanthrene

Chrysene a

Naphthalene 2-Methylnaphthalene 1-Methylnaphthalene

Anthracene

2,6-Dimethylnaphthalene

Fluoranthene

2,3,5-Trimethylnaphthalene

Benzo(a)pyrene a

Benz(a)anthracene

a

Perylene

Benzo(b)fluoranthene a

Dibenz(a,c)anthracene

Benzo(k)fluoranthene a

Indeno(c,d)pyrene a

Biphenylene Acenaphthylene Acenaphthene Fluorene a

Carcinogenic PAH according to the Swedish EPA

pounds (Table 2) were identified by comparing their mass spectra and relative retention times with those of reference standards and quantified using the isotope-dilution technique. 2

Results and Discussion

2.1

PAH profiles and concentrations in contaminated soils

The concentrations of PAHs in the soils studied are given in Table 3, whilst Fig. 1 illustrates the PAH profiles (two through six rings) present in each soil sample. Initial PAH concentrations in the soils ranged from 100 to 9300 mg/kg, a span of almost two orders of magnitude. The PAH profiles were less variable and, in general, PAHs with three or four fused aromatic rings together accounted for over 60% of the total. Nevertheless, the soil samples originating from the former wood impregnation industrial sites generally contained greater concentrations (>80%) of PAHs with two to four fused aromatic rings (consistent with published values [20]), whilst the soil sample from the former gas work industrial site contained higher concentrations of HMW PAHs. This may relate to the fact that the gas site was contaminated with coal-tar instead of creosote. An alternative explanation may be that the soil sample from the gas work site was contaminated with PAHs much earlier, and over a longer time period, than the soil samples collected from the wood impregnation industrial sites and this may explain the differing PAH profiles of the soils. The relatively even distribution of two- to six-ringed PAHs exhibited in the soil sample

Fig. 1: Initial soil PAH profiles showing the relative abundance of two through six aromatic ring PAHs. W (wood impregnation), C (coke production) and G (gas work)

collected from the coke-producing industrial site (which was still in use when the samples were collected) may indicate a 'young' PAH profile, since environmental processes such as natural degradation and evaporation are known to cause a reduction in the concentrations of LMW PAHs [21,22]. 2.2

PAH degradation

As the concentration of PAHs in the aqueous phase was negligible (< 1%) following chemical oxidation treatment, the relative effectiveness of the Fenton's reagent and ozone treatments were assessed by calculating the residual concentrations of PAHs in the solid phase. Overall, Fenton's reagent was more effective than ozone in degrading PAHs, at the conditions used in this study. The Fenton's reagent proce-

Table 3: Soil PAH concentrations and standard deviations (based on triplicate measurements) before and after Fenton's reagent and ozone treatment

Soil sample 1 (W) 2 (W) 3 (W)

Start concentration (mg/kg) (± stdev)

After Fenton's reagent (mg/kg) (± stdev)

After Ozone (mg/kg) (± stdev)

3400 ± 136

460 ± 23

1900 ± 152

9300

a

1500

a

1300 310

a a

3000 a 1100 a

4 (C)

510 ± 77

270 ± 111

430 ± 4

5 (W)

1600 ± 256

580 ± 23

1200 ± 132

6 (W)

2800 ± 252

1400 ± 70

2200 ± 220

7 (W)

820 ± 33

490 ± 78

730 ± 131

8 (W)

1400 ± 70

590 ± 201

910 ± 27

9 (G)

140 ± 48

74 ± 9

91 ± 12

a

Single sample

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Degradation of PAHs in Soils

Research Articles

Fig. 2: Graph of the PAH degradation efficiency of Fenton's reagent and Ozone for the nine soil samples. (* not statistically significant from start concentration, p= 0.1, one-tailed t-test)

dure was performed under conditions of high temperature and oxidant load and resulted in the removal of 40% to 86% of PAHs in the solid soil material. Oxidation using ozone resulted in the removal of between 10% and 70% of the PAHs in the solid soil material, despite the use of ethanol to enhance the desorption process (Fig. 2). The heterogenic nature of the soils necessitated a statistical assessment of oxidation efficiency. The results demonstrate that, at the 0.10 significance level, significant degradation of PAHs in the solid material of soil could not be proven for soil sample (4C, and 9G) treated with ozone. Soil LMW PAHs were degraded more effectively than HMW PAHs using ozone as the oxidant (Fig. 3). This was consistent with expectations because HMW PAHs are more strongly sorbed to the soil matrix and soil-bound contaminants resist oxidation more effectively than contaminants in solution [12,15]. However, the results of the present study indicate that PAH size exerts little influence on the degree of degradation achieved using Fenton's reagent (see Fig. 3). This may be explained by the high oxidant load used in this study [14,23]. Watts et al. [14] suggests that the use of a high oxidant load results in the generation of (as yet) unidentified species that are capable of oxidising sorbed contaminants. Since milder oxidation methods are more dependent on the desorption of contaminants prior to degradation [12], attempts have been made in many studies to increase the desorption of HMW PAHs, in particular, from soils using vegetable oil or alcohol, for example [17]. Since ozone was performed under milder oxidation conditions than for Fenton's reagent, it is therefore

Fig. 3: Average degradation efficiencies of two through six ring PAHs with Fenton's reagent (
) and Ozone (
) in all nine soil samples

212

reasonable to assume that a greater difference in the degree of degradation of LMW and HMW PAHs would have been observed if ethanol had not been added during the ozone treatment. Nevertheless, in this study an increase in the relative concentration of HMW PAHs was observed in the soil samples after treatment with ozone, as HMW PAHs are less susceptible to oxidation using this technique. The effectiveness of PAH degradation was highly dependent on the initial concentrations of PAHs in the soil, with greater PAH degradation observed in soils that contained high initial concentrations of these contaminants (Fig. 4). This phenomenon has been observed previously in sorption studies performed on soils that contained PAHs introduced in the laboratory in order to determine PAH bioavailability [22, 24,25]. However, there was no clear correlation between the degradation efficiency of PAHs with two through to six fused aromatic rings and their respective initial concentrations. Organic compounds sorb on the soil matrix in a nonlinear fashion, suggesting that sorption sites can become saturated when soil PAH concentrations are high [26]. The saturation of soil sorption sites in soils with high initial PAH concentrations suggests that greater quantities of PAHs would become chemically available and therefore higher degradation should be achieved. The data presented here appear to support this hypothesis. None of the soil samples in this study contained PAH concentrations at or below the current Swedish EPA regulatory

Fig. 4: Influence of initial PAH concentration on the degradation efficiency of PAHs with Fenton's reagent (
) and Ozone (
). R2 values for Fenton's reagent and ozone were 0.45 and 0.71, respectively

J Soils Sediments 6 (4) 2006

Research Articles limit of 7 mg carcinogenic PAHs/kg soil [2] after treatment. This is despite the fact that, in some cases, chemical oxidation treatment reduced PAH concentrations by over 80%. Soil samples one and seven, which exhibited the highest and lowest degradation levels, respectively, were subjected to a second oxidation cycle, using Fenton's reagent as the oxidant. However, no significant further reduction in PAH concentrations was observed, indicating that the residual PAHs are strongly sorbed to the soil. This demonstrates that a sitespecific risk assessment may be appropriate after contaminated soils have been chemically treated. Fenton's reagent and ozone are often proposed as promising chemical oxidation methods with potential use as in situ techniques. However, their use has been limited because of technical uncertainties and regulatory barriers [4]. If such obstacles could be removed it is likely that both ozone treatment and treatment with Fenton's reagent would be most suitable soil remediation techniques. The type of treatment used would however depend on pollutant levels, soil characteristic and time available for the remediation. The fastest results would be obtained using ex situ or on site batch treatment under harsh conditions, as those applied in the present study. However, if time would be less critical than treatment cost, it is reasonable to expect that the oxidant load may be reduced (as would the treatment cost) by using in situ treatment. Finally, it is worth pointing out that a thorough site characterisation is crucial for an efficient and cost effective remediation [27] and it is therefore surprising that few studies have been performed using soils collected from contaminated sites. In order to further investigate contaminant sequestration and chemical availability, it is imperative to include aged soils contaminated with multiple PAHs as well as soil samples artificially contaminated in the laboratory, in future remediation studies. 3

Degradation of PAHs in Soils be strongly sorbed to the soil matrix and therefore chemically unavailable. Further, the low concentrations of PAHs observed in the liquid phase indicated that desorbed PAHs were either oxidised rapidly or resorbed in the soil matrix. None of the soil samples in this study, either before or after treatment, contained PAH concentrations at or below the current Swedish EPA regulatory limit. This study has clearly demonstrated the importance of including aged contaminated soils in chemical degradation studies. The degree of PAH degradation varied greatly in the soils studied, which can largely be explained by the multitude of differing PAH compounds encountered in the soils from the different industrial sites and the large variation in initial soil PAH concentrations. In addition, some of this variability may be due to the chemical and physical properties of the PAH contaminants, and the characteristics of the soils studied, as well as the time-period over which the PAHs have been associated with the soil. All of these factors will influence, to some degree, the chemical availability of PAHs and, consequently, the effectiveness of any remediation efforts. It is therefore the intention to investigate these parameter and their potential influence on the chemical oxidation efficiency in future chemical remediation work. 4

Recommendations and Perspectives

Due to the vast number of contaminated sites there is a great need of efficient remediation methods throughout the world. This study shows the difficulties which may be experienced when applying remediation methods to a variation of contaminated sites. Therefore, we recommend including aged contaminated soils in chemical degradation studies. In future chemical remediation work, we intend to investigate the potential influence of the chemical and physical properties of PAHs and soil parameters potential influence on the chemical oxidation efficiency in aged contaminated soils.

Conclusions

This study has demonstrated that the efficiency of degradation using Fenton's reagent and ozone is highly dependent on the initial concentration of PAHs in soils and the particular compounds present. The highest degradation efficiencies were achieved in soil samples taken from wood impregnation industrial sites, probably due to the relatively high concentrations of LMW PAHs and high initial PAH concentrations in the soils from these sites. Significant PAH degradation efficiencies were observed in soils with relatively high initial concentrations of PAHs and this is thought to be a consequence of the saturation of sorption sites. Overall, at the conditions used in this study Fenton's reagent was found to be more effective than ozone in degrading PAHs. In addition, Fenton's reagent degraded large PAHs more effectively, probably because the desorption dependency is lowered by the strong oxidation conditions. Ozone treatment yielded a higher degradation of LMW PAHs, but this resulted in the relative enrichment of HMW PAHs in the residual soil. The remaining PAHs in soils after both Fenton's reagent and ozone treatment appear to

J Soils Sediments 6 (4) 2006

Acknowledgements. This study was supported by the northern Sweden Soil Remediation Centre (MCN), which is partially funded by the European Union Regional Development Funds (ERDF), New Objective 1. Contract Numbers: 113-12534-00, 304-12732-2004, 304-12738-2004.

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Further Literature

Antiƒ MP, Jovanciceviƒ B, Iliƒ M, Vrviƒ MM, Schwarzbauer J (2006): Petroleum pollutant degradation by surface water microorganisms. Environ Sci Pollut Res 13 (5) 320–327 Booth L, Heppelthwaite V, O'Halloran K (2005): Effects-based assays in the earthworm Aporrectodea caliginosa: Their utilisation for evaluation of contaminated sites before and after remediation. J Soils Sediments 5 (2) 87–94 Chaudhry Q, Blom-Zandstra M, Gupta SK, Joner E (2005): Utilising the synergy between plants and rhizosphere microorganisms to enhance breakdown of organic pollutants in the environment. Environ Sci Pollut Res 12 (1) 34–48 Jones R, Sun W, Tang C-S, Robert F (2004): Phytoremediation of petroleum hydrocarbons in tropical coastal soils – II. Microbial response to plant roots and contaminant. Environ Sci Pollut Res 11 (5) 340–346 Jovanciceviƒ B, Antiƒ MP, Soleviƒ TM, Vrviƒ MM, Kronimus A, Schwarzbauer J (2005): Investigation of interactions between surface water and petroleum type pollutants. Environ Sci Pollut Res 12 (4) 205–212 Kammann U (2006): PAH metabolites in bile fluids of Dab (Limanda limanda) and Flounder (Platichthys flesus): Spatial distribution and seasonal changes. Environ Sci Pollut Res OnlineFirst Shen G, Cao L, Lu Y, Hong J (2005): Influence of phenanthrene on cadmium toxicity to soil enzymes and microbial growth. Environ Sci Pollut Res 12 (5) 259–263 Sun W, Lo J, Robert F, Ray C, Tang C-S (2004): Phytoremediation of petroleum hydrocarbons in tropical coastal soils – I. Selection of promising woody plants. Environ Sci Pollut Res 11 (4) 260–266 Trably E, Patureau D (2006): Successful Treatment of Low PAHContaminated Sewage Sludge in Aerobic Bioreactors. Environ Sci Pollut Res 13 (3) 170–176 Vaajasaari K, Joutti A (2006): Field-Scale assessment of phytotreatment of soil contaminated with weathered hydrocarbons and Heavy Metals. J Soils Sediments 6 (3) 128–136 Zechmeister HG, Dullinger S, Hohenwallner D, Riss A, HanusIllnar A, Scharf S (2006): Pilot study on road traffic emissions (PAHs, heavy metals) measured by using mosses in a tunnel experiment in Vienna, Austria. Environ Sci Pollut Res 13 (6) 398–405 Received: May 17th, 2006 Accepted: August 24th, 2006 OnlineFirst: August 25th, 2006

J Soils Sediments 6 (4) 2006