Remediation of highly contaminated soils from ... - Suprahumic - Unina

Journal of Hazardous Materials 261 (2013) 55–62

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Remediation of highly contaminated soils from an industrial site by employing a combined treatment with exogeneous humic substances and oxidative biomimetic catalysis Filomena Sannino a,∗ , Riccardo Spaccini a,b , Davide Savy a , Alessandro Piccolo a,b a

Dipartimento di Agraria, Università di Napoli “Federico II”, Via Università 100, 80055 Portici, Italy Centro Interdipartimentale di Ricerca sulla Risonanza Magnetica Nucleare per l’Ambiente, l’Agro-Alimentare ed i Nuovi Materiali (CERMANU), Via Università 100, 80055 Portici, Italy b

h i g h l i g h t s • • • •

Remediation of two polluted soils from a highly contaminated industrial site in Italy. Restoration of soil quality by introducing additional carbon into polluted soil with humic matter amendments. Detoxification of contaminants by covalent binding to humic molecules. Prevention of environmental transport of pollutants.

a r t i c l e

i n f o

Article history: Received 3 April 2013 Received in revised form 10 June 2013 Accepted 30 June 2013 Available online xxx Keywords: Soil remediation Oxidative biomimetic catalysis Humic substances

a b s t r a c t Remediation of two polluted soils from a northern Italian industrial site heavily contaminated with organic contaminants was attempted here by subjecting soils first to addition with an exogenous humic acid (HA), and, then, to an oxidation reaction catalyzed by a water-soluble iron-porphyrin (FeP). An expected decrease of detectable organic pollutants (>50%) was already observed when soils were treated only with the H2 O2 oxidant. This reduction was substantially enhanced when oxidation was catalyzed by iron-porphyrin (FeP + H2 O2 ) and the largest effect was observed for the most highly polluted soil. Even more significant was the decrease in detectable pollutants (70–90%) when soils were first amended with HA and then subjected to the FeP + H2 O2 treatment. This reduction in extractable pollutants after the combined HA + FeP + H2 O2 treatment was due to formation of covalent C C and C O C bonds between soil contaminants and amended humic molecules. Moreover, the concomitant detection of condensation products in soil extracts following FeP addition confirmed the occurrence of free-radical coupling reactions catalyzed by FeP. These findings indicate that a combined technique based on the action of both humic matter and a metal-porhyrin catalyst, may become useful to quantitatively reduce the toxicity of heavily contaminated soils and prevent the environmental transport of pollutants. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Agricultural and industrial activities may severely pollute soils with toxic chemicals, such as pesticides, fuels, alkanes, dyes, polycyclic and halogenated aromatic hydrocarbons [1,2]. The ecofriendly and relatively inexpensive bioremediation methods are preferably applied to reduce and possibly eliminate soil contamination [3,4]. However, bioremediation processes are hardly applicable on highly contaminated sites due to the simultaneous presence of several pollutants, which are likely to inhibit microbial

∗ Corresponding author. Tel.: +39 0812539187; fax: +39 0812539186. E-mail address: [email protected] (F. Sannino). 0304-3894/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2013.06.077

activity and consequently pollutants biodegradation. In these cases, bioremediation processes are activated only after a preliminary removal of pollutants by physical or physical–chemical methods [5–7]. Among these methods, soil washing with natural surfactants, such as humic substances (HS), was proved to be very effective in removing most pollutants from a highly contaminated industrial site in Italy [8]. In fact, HS are known to strongly adsorb apolar and medium polar organic contaminants, which are then repartitioned in the humic pseudo-micellar domains [9]. The versatility of humic matter in incorporating environmental contaminants is due to its complex supramolecular conformation which comprises a large number of relatively small molecules with different structure and chemical affinity, which arrange in mostly hydrophobic domains [10–12].

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F. Sannino et al. / Journal of Hazardous Materials 261 (2013) 55–62

HS are known to facilitate degradation of xenobiotics via either photocatalysis [13–15], or enzymatic oxidation [16], or other abiotic/biotic processes [17,18]. The role of HS in removing organic pollutants was recently found to be significantly enhanced in the presence of biomimetic catalytic systems such as metal-porphyrins [19,20]. These biomimetic catalysts are active in the same oxidation reactions as those catalyzed by peroxidase, ligninase, and monoxygenase enzymes [21–23], since the metal-coordinated tetrapyrrolic ring functions as the redox active site and increases the reactivity of oxygen species in metal-oxo complexes [24–27]. Metal-porphyrins are also efficient catalysts in the photo-oxidation of hydrocarbons, alkanes and alkenes, when oxygen is activated under UV light [28]. A water-soluble iron-porphyrin (FeP), with H2 O2 as oxygen donor, was proved to be effective by either homogenous or heterogenous catalyis in increasing the structural rigidity and, hence, molecular size of dissolved HS [29,30]. A similar oligomerization of humic molecules was equally catalyzed by FeP under only solar irradiation, thereby suggesting that dissolved oxygen activate the photo-oxidative coupling of humic components [30,31]. The FeP-catalyzed photo-oxidative polymerization of humic molecules was also found to be effective in situ in soil with consequent reduction of CO2 emission from soils [32,33] and increased carbon sequestration even in field soils under cropping [34]. Similarly, co-polymerization of multi-halogenated phenols in humic molecules was recently shown to occur under FeP oxidative catalysis [35,36]. Based on these findings, it may be inferred that an in situ addition of FeP biomimetic catalyst to contaminated soils freshly amended with humic matter, may improve inactivation of soil pollutants by their covalent binding into humic molecules. The aim of this study was to evaluate whether a soil first amended with an exogenous humic acid, and, then, subjected to an oxidation catalyzed by a water-soluble iron-porphyrin may efficiently reduce heavy industrial soil pollution, and hence become a viable remediation technology. 2. Materials and methods 2.1. Soils Two soil samples (A and B) were collected from the site of ACNA (Aziende Chimiche Nazionali Associate), an industrial area of Cengio (near Savona) in the Northern Italy. The site is extremely polluted due to irregular disposal of organic and inorganic contaminants on surface and lower soil horizons since 1882. The pollution of the area was intensified since 1939 when the manufacture of a range of organic colorants was additionally conducted. In 1999, due to the serious contamination of surrounding soils and waters, the ACNA site was included in the list of national priorities for environmental remediation. Soil samples were air-dried, sieved through 2.00 mm, and then analyzed for the determination of pH and texture according to the official Methods of the

Table 1 Characteristics of soil A and B from the polluted ACNA site.

Coarse sand (%) Fine sand (%) Silt (%) Clay (%) Total organic carbon (%) Nitrogen (%) pH

Soil A

Soil B

21.2 ± 0.6 35.6 ± 0.8 39.6 ± 0.5 3.6 ± 0.2 2.8 ± 0.1 1.2 ± 0.1 7.4

12.8 ± 0.4 38.8 ± 0.5 43.6 ± 0.7 4.8 ± 0.3 2.7 ± 0.2 0.13 ± 0.02 7.4

Soil-FeP (treatment A) FeP Soil-FeP-H2O2 (treatment C)

FeP + H2O2

HA

Soil

FeP Soil-HA (treatment D)

Soil-HA-FeP (treatment E)

H2O2

Soil-HA-FeP-H2O2 (treatment F)

H2O2 Soil-H2O2 (treatment B)

Scheme 1. Treatments on the soils of this study.

Italian National Society of Soil Science [37]. The content of carbon and nitrogen was evaluated by Fisons EA 1108 Elemental Analyzer. Their chemical and physical properties are reported in Table 1.

2.2. Biomimetic catalyst The synthesis and purification of the water-soluble mesotetra-(2,6-dichloro-3-sulfonatophenyl)-porphyrinate of Fe(III) [Fe(TDCPPS)Cl] used here as biomimetic catalyst (FeP) were previously reported [29].

2.3. Humic substances A humic acid (HA) was isolated from a North Dakota Leonardite (Mammoth, Chem. Co., Houston, TX), and purified as described earlier [38]. The HA was then suspended in distilled water and titrated to pH 7.0 by an automatic titrator (VIT 909 Videotitrator, Copenaghen) with a 0.1 M NaOH solution under N2 stream. Titration required 2.66 mequiv of NaOH per g of HA, which represented the HA carboxylic acidity. The resulting sodium-humate was filtered through a Millipore 0.45 ␮m, freeze-dried. This HA contained 2.7% of ashes, 56% C, 4% H, 2% N, and, by difference, 38% O or other elements. The relative standard deviation measured for elemental analyses did not exceed 2%. The carbon distribution and both hydrophobicity and aromaticity of this HA, as obtained by 13 C-CPMAS-NMR spectroscopy, are shown elsewhere [39].

2.4. Addition of exogenous HA and biomimetic catalyst to polluted soils A first series of experiments, without HA, were conducted by placing 20 g of each soil sample in Petri glass dishes, and adding the following solutions: (A) 10 mL of a 1.09 × 10−4 M aqueous solution of FeP catalyst; (B) 10 mL of a 1.29 M freshly prepared H2 O2 solution; (C) both FeP and H2 O2 solutions, in the order, in the same volumes and concentrations as in the previous two experiments (Scheme 1). A second series of experiments, with HA, were conducted by first treating 20 g of soil in Petri glass dishes, with 10 mL of a 1 mg mL−1 HA aqueous solution (D). The soils were left to airdry for 10 days, and then added with the following solutions: (E) 10 mL of a 1.09 × 10−4 M aqueous solution of FeP catalyst solution; (F) 10 mL of both FeP catalyst and H2 O2 solution, in the order, at the same concentration as for the first series of experiments (Scheme 1). In all additions, the final aqueous volume in each Petri glass dish was 20 mL. The treated soils were then incubated at room temperature for 30 days in the dark, in order to prevent any photocatalytic oxidation, and subjected to Soxhlet extractions. All experiments and soxhlet extractions were conducted in triplicate.


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Table 2 Total concentration (mg kg−1 ) of pollutants present in soil A and soil B. Pollutants

Soil A

Soil B

PAH Monoaromatic halogenated and nitrogenated compounds Furans Thiophenes Biphenyls Total

66 ± 8 164 ± 18

1336 ± 55 145 ± 19

43 ± 11 NF 1.0 ± 0.2 298 ± 37

54 4.5 5.5 1548

± ± ± ±

7 0.4 0.3 81

NF = none found.

2.5. Soxhlet extraction of soil contaminants Soil samples (10 g) were weighed in Soxhlet filters and extracted in a Soxhlet equipment under reflux with 100 mL of an acetone/nhexane (1:1, v:v) mixture for 48 h [5]. The organic extracts were rotoevaporated at 40 ◦ C, and redissolved in 5 mL of acetone and 95 mL of ultrapure water. This solution was purified by solid phase extraction (SPE) through elution in Bond-Elute C-18 cartridges (500 mg/3 mL from Varian) with 10 mL of n-hexane, followed by 10 mL of diethyl ether and 10 mL of acetone. The elutes were dried, redissolved with 1 mL of CH2 Cl2 and 1 mL of a 100 ␮g/mL octafluoronaphtalene solution in CH2 Cl2 (internal standard) and analyzed by GC–MS. The concentration of contaminants identified by GC–MS analysis was related to that of octafluoronaphtalene whose detection limit was 5 ␮g/mL. 2.6. Gas chromatography–mass spectrometry (GC/MS) analysis A Perkin-Elmer Autosystem XL gas-chromatograph, equipped with a Programmed-Temperature Split/Splitless injector with programmable pneumatic control kept at a constant temperature of 250 ◦ C, a Restek Rtx-5MS capillary column (5% diphenyl–95% dimethylpolysiloxane, length 30 m, 0.25 mm ID, and 0.25 ␮m df), and a Perkin-Elmer TurboMass Gold mass-spectrometer, was used for qualitative and quantitative analysis of contaminants extracted from the original soils and their residues after the washings. The conditions used for GC analyses were the following: (1) initial temperature of 40 ◦ C for 5 min; (2) to 250 ◦ C at a 3 ◦ C/min rate; (3) isothermal for 20 min. The total GC run time was 95 min. Helium was the carrier gas at 1.5 mL/min with a split-flow of 30 mL/min. The inlet-line temperature of the GC–MS system was set at 280 ◦ C, while that of the MS source at 180 ◦ C. A solvent delay time of 5 min was applied before acquisition of the mass spectra to prevent filament injuries. Low and high m/z limits of mass spectrometer were set at 50, and 400 amu, respectively. A NIST mass spectral library version 1.7 was used for peak identification. Each GC–MS analysis was done in duplicate and quantitative results obtained by GC–MS were weight-averaged to provide experimental error. The relative standard deviation never exceeded 4%. 3. Results and discussion The two soils collected from the ACNA contaminated site showed some differences in general properties (Table 1). While carbon and nitrogen content was similar in both soils, texture distribution was substantially different. In particular, soil A had a larger percentage of coarse-sized particles (21.2%), whereas fine-sand, silt and clay fractions were greater in soil B. The two soils differed largely in type and content of pollutants (Table 2). Soil A had a total amount of organic contaminants (298 mg kg−1 ) four times less than soil B (1548 mg kg−1 ). The

Fig. 1. Total contaminants (mg kg−1 ) found in (a) soil A and (b) soil B. Soils were either untreated or separately treated with FeP; H2 O2 ; FeP + H2 O2 ; HA; HA + FeP; HA + FeP + H2 O2 .

most abundant pollutants identified in soil A were the monoaromatic halogenated and nitrogenated compounds, followed, in the order, by polycyclic aromatic hydrocarbons (PAH), and lesser amounts of furans and biphenyls. Conversely, soil B revealed a large content of PAH followed, in order of abundance, by monoaromatic halogenated and nitrogenated compounds, furans, biphenyls and thiophenes. The different pollutants content could be explained by considering the history of the two soils, as a matter of fact the irregular disposal of contaminants on surface and lower soil horizons led to their unequal distribution and consequently to diverse concentrations found in two soils [8]. The physical–chemical properties of the two soils were not affected by the received treatments (Table 1), whereas the amount of pollutants in soil A and B was greatly altered. The total concentration of contaminants found in soil A and B before and after treatments are shown in Fig. 1a and b, respectively. A considerable removal of organic pollutants (46.5%) was observed for soil A treated either with H2 O2 alone or in combination with iron-porphyrin (FeP + H2 O2 ). It is well known that among various oxidants employed in ISCO (In Situ Chemical Oxidation) technologies, H2 O2 is the most widely used. It dissociates into strong reactants to rapidly destroy many organic compounds [40]. Moreover, in the presence of ferrous ions in soil, hydrogen peroxide can also react as a Fenton’s reagent and accelerate the production of more hydroxyl radicals as powerful oxidants for the decomposition of petroleum hydrocarbons [41]. However, the release of gases bring to the subsidence of the ground and this may have a negative effect on the activity of indigenous/or exogenous microrganisms. Therefore, the H2 O2 treatment most likely decreased detectable contaminants due to oxidative process in which hydrogen peroxide oxidizes the organic pollutants by accepting electrons and it in turn becomes reduced. The combined action of FeP and H2 O2 should be attributed to transformation of pollutants by radical-based oxidative reactions catalyzed by FeP [24,42,43].

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Fig. 2. Peroxide shunt pathway for organic substrates (SH) in the Fe(III)-P/H2 O2 system.

In fact, as reported in Fig. 2, hydrogen peroxide is a single oxygen donor that is required to produce the highly reactive oxo-iron(IV)porphyrin radical cations, which are the key intermediates to form the strong oxidizing species in the catalyzed oxidation of organic substrates (SH) by P-Fe(III) via the peroxide shunt (Fig. 2) [19]. Consequently, the reduction of [P•+ -Fe(IV) O] by SH can yield PFe(IV) O and radical species derived from the substrate (S• ). The second electron transfer from the substrate to P-Fe(IV) O results in the return P-Fe(III) to the initial state. The substrate radical species then couple to other free radicals, thereby forming intermolecular covalent bonds.

A decrease in detectable pollutants, though to a lesser extent (about 17%), was also shown when soil A was added with either HA alone or FeP after HA addition, without any significant difference between these two treatments. This effect should be attributed to a physical incorporation of contaminants into the hydrophobic domains of HA, thus making them less soluble in the organic solvents used in the Soxhlet extraction [8]. The largest significant decrease in extractable contaminants (69.6%) was instead recorded when soil A was first amended with HA and, then, subjected to the full oxidative catalytic reaction (HA + FeP + H2 O2 ). Soil B (Fig. 1b) showed the same behavior as soil A, although a more extensive reduction of detectable compounds was noted for this soil, probably because of its greater content of pollutants. In fact, the decrease in extractable contaminants was about 60% for the H2 O2 and FeP + H2 O2 treatments, and still around 28% for samples treated with either HA or HA + FeP. Conversely, the reduction in detected contaminants was more than 90% when the HA amendment to soil B was combined with the full oxidative catalytic reaction (HA + FeP + H2 O2 ). The effectiveness of treatments can be clearly inferred from GC/MS chromatograms. Those for soil A extracts, either untreated or treated with the FeP + H2 O2 mixture after HA amendment, are shown in Fig. 3a and b, respectively. Peaks corresponding to several classes of contaminants, which were detected in the untreated soil (Fig. 3a; Table 3), mostly disappeared in the chromatogram of the HA-amended sample after its treatment with the full oxidative catalytic reaction (FeP + H2 O2 ) (Fig. 3b). Furthermore, the appearance of new signals at 54.08, 68.18–70.01, and 87.43 min in the chromatogram of the latter sample (Fig. 3b), indicated formation of new reaction products (Table 3). Similar peaks were observed also in the chromatogram of extracts from soil A treated with only FeP, thus indicating that the biomimetic catalyst was active even without addition of the H2 O2 oxidant [24,31]. The GC/MS chromatograms of soil B for either the control sample or the HA-amended sample subsequently treated with the

Table 3 Retention times (RT) of compounds identified in the GC–MS chromatograms for soil A of either untreated or treated samples. RT (min)

Compound

Untreated soil

FeP

H2 O2

FeP + H2 O2

HA

HA + FeP

HA + FeP + H2 O2

15.65 16.27 19.23 23.08 23.82 24.92 25.75 27.68 32.36 34.19 43.01 44.92 48.04 53.48 54.08 58.43 59.46 62.02 63.21 64.49 66.79 67.43 70.01 70.12 71.17 71.90 74.32 87.43

Naphtalene Naphtalene Naphtalene-methyl Naphtalene-1-methyl Naphtalene-2-methyl Benzonitrile-2,6-dichloroBenzene-1-methoxy-2-nitro Diphenylether Benzene-dodecyloxynitroNaphtalene-1,4,6-trimethyl2,3,4,5,6-Pentachloroaniline 1,2-Benzene-dicarboxylic acid, butyl 2-methylpropylester 1,2-Benzene-dicarboxylic acid, butyl 2-methylpropylester Alkanoic acid Anthracenedione Ethyl-benzoanthracene 4,6 -Biazulenyl Benzoanthracene 1,1 -Binaphtalene 1,2-Benzene-dicarboxylic acid, mono(2ethylhexyl)ester 1-(2-Naphtalenyloxy)-naphthalene 9,10-Dihydro-9-oxo-10-phenylanthracene Benzofluorenone Dinaphtofuran Naphthalene, 1-(2-naphtalenylmethyl) Dinaphtofuran Biazulenyl 1,2-Benzenediol, 3,5-bis (1,1 dimethylethyl)-

x x x x x x x x x x x x x x NF x x x x x x x NF x x x x NF

x x x x x x x x x x x x x x NF x x x x x x x NF x x x x NF

x x x x x x x x x x x x x x x x x NF x x x NF x x x x x x

x x x x x x x x x x x x x x x x x NF NF x x NF x x x x x x

NF NF x x x x x x x x x x x x x x x NF x x x x NF x x x x NF

NF NF x x x x x x x x x x x x x x x NF x x x x NF x x x x NF

NF NF NF NF NF NF NF NF NF NF x x NF NF x NF NF NF NF NF x NF x NF x NF NF x

x = found. NF = none found.


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Fig. 3. GC–MS chromatograms of soil A either (a) untreated or (b) treated with the combined humic and catalytic (HA + FeP + H2 O2 ) technology. Both chromatograms were magnified 10-fold. 䊉 = PAH; = monoaromatic halogenated and nitrogenated compounds; = furans; = biphenyls; ♦ = sulphones; = alkanoic acid.

FeP + H2 O2 mixture (Fig. 4a and b), showed a similar behavior as soil A. As noted earlier, the decrease of pollutants in soil B was more evident than in soil A and so was the appearance of new peaks (Table 4), thus confirming the effectiveness of the catalytic reaction mixture in soil samples which received a preliminary addition with HA. The presence of condensation products (e.g.: anthracenedione and benzofluorenone) in soil extracts following addition of FeP to soil samples (Tables 3 and 4) suggests that some contaminants

may have been self-coupled through the oxidative formation of free-radicals promoted by FeP catalysis [25]. This finding combined with the observed drastic reduction of detectable pollutants in soils which were first added with HA and then treated with the FeP–H2 O2 mixture (Fig. 1), implies that the catalyzed oxidative reaction favored the formation of covalent bonds between contaminants and humic molecules. The reaction mechanism by which FeP exerts its catalysis requires an oxygen donor (H2 O2 ) to produce a cationic

60


Fig. 4. GC–MS chromatograms of soil B either (a) untreated or (b) treated with the combined humic and catalytic (HA + FeP + H2 O2 ) technology. Both chromatograms were magnified 20-fold. 䊉 = PAH; = monoaromatic halogenated and nitrogenated compounds; = furans; = biphenyls; ♦ = sulphones; = alkanoic acid; = thiophenes.

radical oxo-iron(IV)-porphyrin [P•+ -Fe(IV) O], whose high valence becomes an active oxidant of pollutants [23,25,44,45]. Freeradicals species formed during oxidation then undergo coupling reactions leading to formation of stable C C or C O C covalent bonds and larger-size molecules. This mechanism should explain the significant decrease of detectable pollutants observed in both soils when subjected to the full HA + FeP + H2 O2 treatment (Fig. 1). Formation of chlorinated intermediates, such as chlorophenoxy radicals, was already shown when iron-porphyrin had been used to catalyze the oxidation of pentachlorophenol (PCP) in the presence of HS [19]. Moreover, HS induced the disappearance of PCP-derived dimers which have been coupled during the FeP catalyzed oxidation reaction, while more than 60% of the chlorine

released from PCP was found in HS. These findings were confirmed by other results [35], which showed that the FeP-catalyzed reaction promoted the disappearance of PCP through formation of covalent bonds between the de-chlorinated phenol and HS, rather than by simple PCP de-chlorination. A permanent incorporation of pollutants into HS catalyzed by the peroxidase enzyme had been suggested earlier [46] on the basis of 13 C NMR spectra of 13 C-labeled 2,4-dichlorophenol (DCP). Moreover, the biological detoxification of DCP was also noted [20] when the FeP oxidative catalysis was conducted in the presence of HS, and was attributed to the covalent binding of DCP to HS. On the other hand, our results are in agreement with the size increase observed for dissolved humic molecules when FeP was used either under chemical- or photo-oxidation. Such effect was explained with the self-coupling


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Table 4 Retention times (RT) of compounds identified in the GC–MS chromatograms for soil B of either untreated or treated samples. RT (min)

Compound

Untreated soil

FeP

H2 O2

FeP + H2 O2

HA

HA + FeP

HA + FeP + H2 O2

16.92 25.17 26.37 30.71 35.48 37.37 39.15 40.49 42.60 42.97 44.98 45.99 47.37 47.92 48.39 53.37 55.55 51.65 53.75 57.36 58.47 60.75 60.85 61.22 62.04 63.41 63.88 64.98 65.62 66.81 67.18 68.28 78.92 82.04 84.42

Naphtalene 1,2,3,4-Tetrachlorobenzene p-Hydroxybiphenyl Alkanoic acid Alkanoic acid Hexachloro-benzene Benzene, pentachloronitroAlkanoic acid 2,3,4,5,6-Pentachloroaniline 1,2-Benzenedicarboxylic acid, bis(2-methylpropyl)ester Alkanoic acid 1,2-Benzenedicarboxy lic acid, bis(2-methylpropyl)ester 2-Phenylmethyl-naphtalene 2-Phenylmethyl-naphtalene Anthracenedione 2-Chloro-anthracenedione Benzofluorenone 1,3-Cyclopentadiene, 1,3-dimethyl-5,5-diphenylChrysenol 1,1 -Binaphtalene 1,2 -Binaphtalene Benzoanthracene 4,6 -Biazulenyl 1,1 -Oxybis-naphtalene 1-Pyrene-carboxaldehyde Benzoanthracenone 1,1 -Binaphtalene-2,2 -diol Benzoanthracene-12-carboxaldehyde, 7-methylNaphto thiophene, 2-phenyl 4-Methoxyphenyl 6-methyl 1,3-benzodioxol-5-yl 4H-1-benzopyran-4one, 3-(3,4-dimetoxyphenyl)-6,7-dimethoxy Dinaphtofuran Binaphthylsulfone Benzothiophene Dinaphtopyran-7-one

x x x x x x x x x x x x x x NF NF NF x x x x x x x x NF x x x NF NF x x x NF

x x x x x x x x x x x x x x x NF NF x x x x NF x NF NF x NF NF x NF NF NF NF x NF

x x x x x x x x x x x x x x x x NF x x x x NF x NF x NF x x x NF NF NF NF NF NF

x x x x x x x x x x x x x x x x NF x x x x NF x x NF x NF NF x NF NF NF NF x NF

NF x x x x x x x x x x x x x x NF NF x x x x x x x x NF x x x x x x NF NF x

NF NF NF x x NF x x x x x x x x x NF NF x x x x x x x x x x x x NF NF x x x NF

NF NF NF x x NF NF x x x x x x x x NF x NF NF x x NF NF x NF x x NF x x x x NF NF x

x = found. NF = none found.

polymerization of humic phenolic components via a free-radical mechanism [29,31]. 4. Conclusions In this study, we showed that the remediation of two aged highly polluted soils from an industrial site may be efficiently accomplished by a combined technology, that encompasses first a soil treatment with an exogenous humic acid, and, then, a binding of contaminants into the added humic molecules through an oxidative coupling reaction catalyzed by a water-soluble iron-porphyrin. Comparison of GC–MS chromatograms of untreated soils with those of soils amended with HA and then treated with the oxidative biomimetic catalysis, indicated that humic matter addition significantly enhanced the disappearance of contaminants from the soils subjected to the combined technique. In fact, free-radicals species formed in soil during the FeP-catalyzed oxidation reaction, must have induced both mutual coupling among pollutants, and formation of new covalent bonds between pollutants and humic molecules, thus promoting a stable incorporation of contaminants into the supramolecular structure of humic matter. We should reasonably expect that, despite these results are based on specific contaminated substrates which hardly resemble proper soils, similar remediation effects can be obtained by such combined technique on soils of different chemical and physical characteristics. We conclude that the direct application of a water-soluble metal-porphyrin catalyst on a polluted soil that is previously amended with exogenous humic matter, may hence represent an innovative and rather efficient method to reduce the excessive soil contamination in aged industrially polluted soils. Moreover,

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