REGULAR ARTICLE

Distribution patterns of selected PAHs in bulk peatand corresponding humic acids from a Swiss ombrotrophicbog profile

C. Zaccone & A. Gallipoli & C. Cocozza &

M. Trevisan & T. M. Miano

Received: 16 June 2008 /Accepted: 3 September 2008 / Published online: 20 September 2008# Springer Science + Business Media B.V. 2008

Abstract An ombrotrophic peat core was collected in2005 from Etang de la Gruère, Jura Mountains,Switzerland. The concentrations of nine among theU.S. Environmental Protection Agency priority poly-cyclic aromatic hydrocarbons (PAHs) (i.e., acenaph-thene, phenanthrene, fluorene, pyrene, fluoranthene,benzo[jbk]fluoranthene, benzo[a]pyrene, benzo[ghi]perylene, and indeno[1,2,3-cd]pyrene) were deter-mined in both bulk peat and corresponding humicacids (HA) samples by gas chromatography equippedwith a mass spectrometry detector (GC-MS). Themaximum PAHs concentrations in peat (around1,250 μg Σ PAHs kg−1 dry matter) were found at28–30 cm of depth, which correspond to ca. 1920–1930, when coal inputs to Switzerland reached theirmaximum level. Amongst the nine PAHs analyzed inthe peat samples, pyrene (Pyr) was the predominantspecies, accounting for ca. 20–100% of the totalPAHs throughout the profile. In the HA fraction, that

represents 24.7% (average value) of the bulk peat,only phenanthrene (Phe), and sporadically Pyr andfluoranthene (Fth), were detected. In particular, HAshowed Phe concentrations that were ten–150 timeshigher than corresponding bulk peat samples, thussuggesting its preservation against biodegradation dueto the incorporation into HA molecules.

Keywords Atmospheric depositions . GC-MS .

Humic substances . Phenanthrene . Polycyclic aromatichydrocarbons . Trace elements

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are aubiquitous group of persistent and toxic organiccontaminants formed as incomplete combustion pro-cesses due to both natural and anthropogenic sources(Nadal et al. 2004). Main natural sources includeforest and prairie fires, natural petroleum seeps, andpost-depositional transformations of biogenic precur-sors, while anthropogenic ones mainly include com-bustion of fossil-fuel and long-range atmospherictransport of PAHs adsorbed onto airborne particulatematter, vehicular emissions and spillage of petroleumand its refined products (Pereira et al. 1999). Accord-ing to their genesis, PAHs can be classified in threemajor types: petrogenic, biogenic, and pyrogenic. Indetail, (i) PAHs of petrogenic origin (e.g., naphthalenes,phenanthrenes, and dibenzothiophenes) are related topetroleum, including crude oil and its refined products

Plant Soil (2009) 315:35–45DOI 10.1007/s11104-008-9775-1

Responsible Editor: Ingrid Koegel-Knabner.

C. Zaccone (*) : C. Cocozza : T. M. MianoDepartment of Biology and Chemistry of Agro-Forestryand Environment, University of Bari,Via Amendola 165/A,70126 Bari, Italye-mail: zaccone@agr.uniba.itURL: http://www.claudiozaccone.net

A. Gallipoli :M. TrevisanIstituto di Chimica Agraria ed Ambientale,Università Cattolica del Sacro Cuore,Via Parmense 84,29100 Piacenza, Italy

(e.g., the presence of naphthalene and its alkyl-substi-tuted homologues in sediments is characteristic ofunweathered petroleum, Robertson 1998); (ii) PAHsof biogenic origin are generated by biological process-es (e.g., plant- and microbial-related sources of naph-thalene, phenanthrene, and perylene) (Wilcke 2000;Krauss et al. 2005) or by the early stages of diagenesisin marine sediments (e.g., perylene) (Venkatesan1988); while (iii) PAHs of pyrogenic origin aregenerated by the combustion of fossil fuels and ofrecent organic material (Page et al. 1999). In general,PAHs from petrogenic origin consist predominantly ofthose with lower molecular weights (two to threerings), whereas PAHs from pyrogenic origin showhigher molecular weights (four to six rings) (Yang et al.1998; Dahle et al. 2003; Qiao et al. 2006). Conse-quently, the relative abundance of different PAHs canbe used to help distinguish between petrogenic andpyrogenic sources (Robertson 1998; Dahle et al. 2003).

The increasing concern over PAHs stems fromseveral of their characteristics that impact humanhealth and the environment. In fact, these organicpollutants (1) are highly carcinogenic and mutagenic(IARC 1983); (2) have high occurrence of contami-nation and potential for bioaccumulation (Srogi2007); (3) show a relatively low solubility in water,and are highly lipophilic (Srogi 2007); and (4) arerecalcitrant to biodegradation, showing a degradationtime, DT50, that generally increases with PAHs’degree of condensation (Thiele-Bruhn and Brümmer2005). In the environment, PAHs may associate withparticulates and dissolved organic matter and depositonto sediments (e.g., peatlands, lakes), the latter beinga huge sink for air and waterborne contaminants thatreflect the inputs for an ecosystem (Qiao et al. 2006).

Peatlands are waterlogged areas where the rate ofbiomass production is greater than the rate of decom-position, thereby resulting in effective sinks of atmo-spheric carbon (Clymo 1984). The low decompositionrate in these environments mainly depends on the harshenvironmental conditions such as acidic pH, lowtemperature and frequent lack of oxygen (Johnsonand Damman 1993). Ombrotrophic bogs are domedpeatlands supplied only by atmospheric deposition(Damman 1978; Clymo 1983). For that reason, suchdeposits have been often used as a record of theimpact of historical human activity in causing traceelements contamination (e.g., Shotyk et al. 1996,1998; Martínez-Cortizas et al. 1999; Zaccone et al.

2007a) and/or as tool in palaeoclimatic and palae-ovegetation reconstructions (e.g., van Geel 1978;Moore et al. 1991). In addition, undisturbed bogprofiles represent an ideal medium also for recordingtemporal changes in organic contaminant depositionrates (Rapaport and Eisenreich 1988). In fact, since peatfrom bogs generally shows organic matter (OM)concentrations higher than 95–98% and anoxic, acidic(pH ∼4) porewaters (e.g., Cocozza et al. 2003; Zacconeet al. 2007b), the adsorption of hydrophobic organiccontaminants is strongly enhanced and the microbialactivity slowed down, thus minimizing the potential forpost-depositional mobility and/or diagenetic alterationfollowing deposition (Sanders et al. 1995).

Humic acids (HA), the dark-coloured part of OMthat can be extracted from soils and sediments bydilute alkali and that is insoluble in dilute acid(Stevenson 1994), are very important in the formationof stable organo-mineral complexes and, because oftheir amphipathic nature, govern the fate of bothorganic and inorganic pollutants in natural systems(Weber 1988; Stevenson 1994; Senesi and Miano1995). Although several studies have been carried outto reconstruct temporal trends of PAHs using peatcores (e.g., Sanders et al. 1995; Berset et al. 2001)and lake and marine sediments (e.g., Fernández et al.1999; Pereira et al. 1999; Yunker and Macdonald2003), few data are available to date in literatureabout the interaction between these hydrophobicorganic contaminants and the stable, recalcitrant HAfraction along undisturbed profiles. Further, most ofthe studies on the sorption/mobility of PAHs with theincrease of the humic substances (HS) content havebeen carried out on soils (showing low OM content)and by adding exogenous humic material (e.g., Conteet al. 2001). In this work, we focused on thedistribution patterns of selected PAHs in peat andcorresponding HA and on the role of the latterfraction in the accumulation of these persistentcontaminants along an ombrotrophic core (OM>95%) under undisturbed conditions.

Materials and methods

Site features and peat core sampling

Etang de la Gruère is a protected raised bog in theJura Mountains of Switzerland featuring a maximum

36 Plant Soil (2009) 315:35–45

peat accumulation of ca. 650 cm (Joray 1942) thatrepresent more than 12,300 years of formation(Shotyk et al. 1998). This bog is characterised byhigh acidity, and the present vegetation is quite sparseand dominated by Sphagnum species (S. cuspidatum,S. fuscum, S. magellanicum, S. nemoreum, S. papil-losum, S. recurvum, S. rubellum and S. tenellum),although small shrubs, stunted trees, sedges and othermosses are also present (Feldmeyer-Christe 1990).

A core (core 2T; 13×13×105 cm) was collected in2005 from the central domed area of the bog (47°14′22.6″ N; 7°02′57.4″ E) using a Titanium Wardenaarsampler (Wardenaar 1987) (Fig. 1), wrapped in plasticfoils, brought to the laboratory and kept frozen at −18°C until analysis. The score was sliced frozen into 1±0.15 cm sections, and each sample was dried and thenground to <0.25 mm in a centrifugal mill equippedwith a Ti rotor and sieve (Retsch GmbH and Co.,Haan, Germany). The first slices (+3–0 cm) correspondto the living plant material on the bog surface.Chemical, physical, and spectroscopic properties ofthe peat material are reported elsewhere (Zaccone et al.2007b, 2008a).

Peat age dating

The 210Pb activity for age dating was measureddirectly in the topmost dried and ground peat samples(from +3 to −37 cm of depth) using Low Backgroundgamma spectroscopy (GCW4028, HPGE, Canberra),with a minimum of 20 h analysis time. 210Pb was

determined at 46.5 keV; the model used for age datingwas the Constant Rate of Supply (Appleby andOldfield 1978), carried out considering the peat drydensity. The bottom sample was dated using 14C bydecay counting, according to model reported byShotyk et al. (1998).

Humic acids extraction

Humic acids were extracted from peat samplesaccording to a slightly modified procedure of thestandard method proposed by the International HumicSubstances Society (Swift 1996). Briefly, peat sampleswere treated with 0.5 M NaOH+0.1 M Na4P2O7

solution at room temperature for about 12 h, centri-fuged and the supernatant filtered though a WhatmanGF/C glass microfibre filter (1.2 μm pore-size). Theprocedure was repeated for other five times to ensurethat the HA fraction had been extracted exhaustively.The joint extracts were acidified to pH ∼1 with 6 MHCl and allowed to stand for 24 h. The suspensionwas centrifuged and the resultant HA were dialysedagainst Milli-Q water and freeze dried. A moredetailed description of the method has been reportedelsewhere (Zaccone et al. 2007c).

Elemental composition

Total C, N, S and H contents of the peat andcorresponding HA samples were determined, intriplicate, using dry combustion with an elementalanalyzer (Fisons EA1108, Milan, Italy) while theoxygen content (%) was calculated from the differ-ence: O%=100− (C+H+N+S)%. The data werecorrected for moisture and ash contents.

The concentrations of Pb and As, trace elementswhich are commonly enriched in coals (Shotyk et al.1996; Berset et al. 2001; Zaccone at al. 2008b), weredetermined by Energy-dispersive miniprobe X-rayfluorescence multielement (EMMA-XRF) analysisconsisting of a conventional X-ray tube with Moanode, focused concave LiF (220) variable wave-length monochromator, and sample holder. Arsenicand Pb were measured on powered, dried peatsamples with a 600 s analysis time; the limits ofdetection (LOD) were 1 and 0.6 μg g−1, respec-tively. Calibration, accuracy, and precision of thismethod are given elsewhere (Cheburkin and Shotyk1996).

Fig. 1 Details of the Etang de la Gruère bog surface,dominated by Sphagnum species, and of the Wardenaar sampler

Plant Soil (2009) 315:35–45 37

PAHs determination in peat and HA

Glassware treatment In order to reduce the risk ofcontamination, all glassware was previously cleanedin a basic solution and thoroughly washed withdeionized water, oven dried over night at 250°C,and, before the use, rinsed several times with acetoneand hexane. Blanks assessment during test confirmedthat no contaminations occurred.

Solvents, chemicals, and standards Solvents usedwere acetone and hexane, obtained from Fluka(Buchs, Switzerland) at residue analysis quality(PESTANAL). A standard mixture, containing the16 priority PAHs (acenaphtene, acenaphthylene,anthracene, benzo[a]anthracene, benzo[b]fluoran-thene, benzo[k]fluoranthene, benzo[ghi]perylene,benzo[a]pyrene, chrysene, dibenzo[a,h]anthracene,fluoranthene, fluorene, indeno[1,2,3-cd]pyrene, naph-thalene, phenanthrene, pyrene) at a certified concen-tration of 2 mg ml−1 in acetone/benzene 1:1 (v/v), anddeuterated internal standards anthracene-d10 (0.1 g)and perylene-d12 (0.1 g) were purchased fromDr. Ehrensdorfer, Germany. Calibration solutions(0.08–8 mg l−1) were prepared by dilution of thestock solution with hexane. The final concentration ofthe internal standards in the calibration solutions was1.14 mg l−1 for anthracene-d10 and 1.02 mg l−1 forperylene-d12.

Certified reference materials (CRMs) To determinethe efficiency of the method, the certified referencematerial IMEP-21 (sewage sludge) was obtained fromthe European Commission–JRC–IRMM and ana-lyzed. The sludge material, provided by the ReferenceMaterials unit, originates from different sewage plantsin Italy and in France. Environments at these sitesreflect varying degrees of commercial and industrialactivities.

Extraction The samples were prepared by mixingtogether anhydrous sodium sulfate and peats orHA, respectively. The mixture was placed into acellulose extraction thimble and Soxhlet extractedusing a hexane (80%) and acetone (20%) mixturein a full glass system into a boiling water bath.The extract was then concentrated to 10 ml usinga Buchi B-811 Rotavapor. A 5 ml aliquot of theextract was evaporated under gentle flow of

nitrogen, redissolved with 500 μl of hexane,centrifuged and analyzed with GC-MS to deter-mine the presence of benzo[jbk]fluorantene (B[jbk]F, m/z 252), benzo[a]pyrene (B[a]P, m/z 252), benzo[ghi]perylene (B[ghi]P, m/z 276), and indeno[1,2,3-cd]pyrene (InP, m/z 276). The remaining 5 ml of theextract were cleaned-up through a Florisil column,evaporated under gentle flow of nitrogen, dissolvedin 500 μl of hexane, and then analyzed todetermine the presence of acenaphthene (Ace,m/z 153), phenanthrene (Phe, m/z 178), fluorene(Flu, m/z 166), pyrene (Pyr, m/z 202), and fluoran-thene (Fth, m/z 202).

GC-MS analysis GC-MS analysis was performedwith an Agilent Technologies gas chromatograph6890 series equipped with a mass detector MSDAgilent Technologies 5973 series and the dataanalysis station ChemStation. The column used foranalysis was a Supelco SLB-5ms type (5% poly-silarylene–95% polydimethylsiloxane; 30 m×0.25 mm i.d.×0.25 μm film thickness). As carriergas, high grade helium was used at a constant flowrate of 1.0 ml min−1. Injection temperature was 250°C,with a 1 μl as injection volume and 0.5 min as purgetime. The GC-MS oven temperature was maintainedat 140°C, then increased at a rate of 5°C min−1 until200°C. This temperature was maintained for 5 minand finally increased at a rate of 10°C min−1 until280°C and held for 15 min. The detector temperatureswere 150°C (MS quadrupole) and 230°C (MSsource). GC analyses were performed in triplicate.Confirmation of samples was carried out in full scanand SIM mode. Data were acquired from m/z 50 to500.

Quality control Linearity was tested assessing signalresponses of analytes in standard and in matrix over arange of concentrations from 0.08 up to 8.0 μg g−1.The precision of the method was determined by therepeated intra-day analysis on CRM. Recoveryexperiments were performed on a similar matrix(sewage sludge) and on Na2SO4, spiked with 0.1, 1and 4 ppm of PAHs standard solution using the sameprocedure as for peat. Results are summarized inTable 1. The limit of detection (LOD) for PAHs was1 μg kg−1 but, due to the extreme variability ofsample quantities, each sample showed a differentLOD (Table 2).

38 Plant Soil (2009) 315:35–45

Deposition fluxes calculation

The deposition fluxes of PAHs, Pb, As, and S werecalculated, for all samples dated using 210Pb, as theproduct of their concentrations (μg g−1) and the dry

mass accumulation rates to a specific depth of the peatcore (g m−2 year−1). In turn, the dry mass accumulationrates were estimated from the peat dry density (g cm−3)and the growth rate (cm year−1), according to theConstant Rate of Supply model (Appleby et al. 1997).

Table 1 Testing extraction efficiency of the method for PAHs (μg kg−1 dm) using both IMEP-21, as certified reference material, and asewage sludge (uncertified material)

PAH IMEP-21 Uncertified material

Mean S.D. (%) CV Recovery (%) Recovery (%)

Ace n.d. – – n.d. 61Phe 621.9 11.9 746 83 74Flu 82.8 6.6 90 92 66Pyr 897.8 12.8 1,280 70 90Fth 1,038.8 5.6 916 113 95B[jbk]F 915.2 3.3 1,110 83 99B[a]P 379.0 2.4 383 99 92B[ghi]P 534.8 2.8 508 105 105InP 252.3 9.4 370 68 90

Samples have been extracted in triplicate; n=3

Ace Acenaphthene, Phe phenanthrene, Flu fluorene, Pyr pyrene, Fth fluoranthene, B[jbk]F benzo[jbk]fluoranthene, B[a]P benzo[a]pyrene, B[ghi]P benzo[ghi]perylene, InP indeno[1,2,3-cd]pyrene, S.D. standard deviation, CV certified value, n.d. not detected

Table 2 Content of single PAHs (μg kg−1 dry mass) and Σ PAHs in peat samples along the bog profile. Peat dry density and 210Pbage dating are also reported

Peatsamples

Averagedepth (cm)

Dry density(g cm−3)

PAHs Σ PAHs(μg kg−1)

Σ PAHs(mg m−2)

Peat agedating

Ace Phe Flu Pyr Fth B[jbk]F B[a]P B[ghi]P InP

LOD

10 2 12 12 14 12 11 15 15

2T 01 1.5 0.029 n.d. 38.2 119.0 230.4 n.d. n.d. n.d. n.d. n.d. 387.5 0.245 2,005±02T 02 −0.5 0.033 n.d. 75.2 n.d. 243.1 n.d. n.d. n.d. n.d. n.d. 318.3 0.116 2,004±02T 10 −8.0 0.077 n.d. 48.5 75.2 113.5 n.d. 1.6 n.d. n.d. n.d. 238.8 0.153 1,990±22T 12 −9.9 0.077 n.d. n.d. n.d. 290.3 n.d. n.d. n.d. n.d. n.d. 290.3 0.248 1,986±22T 13 −11.0 0.079 n.d. 2.8 n.d. 293.2 n.d. n.d. n.d. n.d. n.d. 296.0 0.261 1,982±22T 21 −19.3 0.058 n.d. 43.4 n.d. 601.6 n.d. n.d. n.d. n.d. n.d. 645.0 0.417 1,959±32T 29 −28.4 0.101 n.d. 49.0 81.4 362.8 80.0 45.7 149.9 476.6 n.d. 1,245.5 1.424 1,929±62T 30 −29.6 0.117 n.d. 26.3 92.0 244.1 n.d. 57.9 309.5 535.3 n.d. 1,265.1 1.691 1,919±62T 31 −30.8 0.114 n.d. 10.8 71.9 120.3 n.d. 12.5 139.2 n.d. n.d. 354.6 0.479 1,901±102T 35 −35.9 0.160 n.d. 3.7 n.d. 73.3 n.d. n.d. n.d. n.d. n.d. 77.0 0.150 1,828±202T 42 −44.6 0.114 n.d. n.d. n.d. 84.1 n.d. n.d. n.d. n.d. n.d. 84.1 0.1252T 50 −54.4 0.092 n.d. n.d. n.d. 87.0 n.d. n.d. n.d. n.d. n.d. 87.0 0.1202T 61 −68.3 0.047 n.d. n.d. n.d. 145.1 n.d. n.d. n.d. n.d. n.d. 145.1 0.0832T 79 −89.4 0.097 n.d. n.d. n.d. 84.5 n.d. n.d. n.d. n.d. n.d. 84.5 0.0782T 87 −98.3 0.103 n.d. n.d. n.d. 70.9 n.d. n.d. n.d. n.d. n.d. 70.9 0.084 2,040±70 14C

year BP

Ace Acenaphthene, Phe phenanthrene, Flu fluorene, Pyr pyrene, Fth fluoranthene, B[jbk]F benzo[jbk]fluoranthene, B[a]P benzo[a]pyrene, B[ghi]P benzo[ghi]perylene, InP indeno[1,2,3-cd]pyrene, n.d. compound not detectable, LOD limit of detection (μg kg−1 )

Plant Soil (2009) 315:35–45 39

Results

Samples characterization and elemental composition

The chemical nature of organic matter is one of themajor factors affecting the PAHs sorption to soils andsediments (Chefetz et al. 2000). The peat sampleswere found to contain 53.1% C, 6.3% H, 1.4% N,39.1% O, 0.1% S, and an ash content of 1.9%(average values). Corresponding HA showed 57.8%C, 5.6% H, 2.2% N, 33.2% O, 0.2% S, and an ashcontent of 1.7% (average values). Compared to HA,peat samples generally exhibit higher O/C ratio(considered to be an indicator of carbohydrates and

carboxylic content), H/C ratio (suggesting a morealiphatic character), and C/N ratio, according toprevious works (Zaccone et al. 2007b, 2008a).

Lead concentration in peat shows highest values inthe first 50 cm (31.2 μg g−1, average value), with amain peak of 89.8±9.0 μg g−1 at ca. 29 cm. Aremarkable decrease in its concentration towards deeperpeat regions, with average values of 3.7 μg g−1 below50 cm, was observed.

Arsenic trend is similar to the Pb one, with higherconcentration values between 8 and 45 cm of depth.In detail, two clear peaks of 7.0±1.5 μg g−1 arepresent at ca. 26 and 29 cm; then, As concentrationdecreases with depth becoming undetectable between

4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.000

50

100

150

200

250

300

350

400

450

500

550

600

650

700

Time-->

Ion 178.00 (177.70 to 178.70): [BSB1]FANA0169.D

4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.000

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

2200

2300

2400

2500

2600

2700

Time-->

Ion 178.00 (177.70 to 178.70): [BSB1]FANA0046.D

Phe Phe

4.00 6.00 8.00 10.00 12. 00 14.00 16.00 18.00 20.00

40000

60000

80000

100000

120000

140000

160000

180000

200000

220000

240000

260000

Time-->

Abundance

TIC: [BSB1]FANA0046.D

4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.000

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

65000

70000

75000

80000

Time-->

Abundance

Abundance Abundance

TIC: [BSB1]FANA0169.D

peat

peat

HA

HA

Fig. 2 Example of total ion chromatograms (on the top) and extracted ion chromatograms (on the bottom) for a peat and a HA sample

40 Plant Soil (2009) 315:35–45

55 and 90 cm. In the deeper layers, that is below90 cm of depth, it is again detectable, although itsconcentrations are close to the LOD.

PAHs concentration in peat and corresponding HA

The concentrations of the studied PAHs in peatsamples are presented in Table 2, while examples oftotal ion chromatograms and extracted ion chromato-grams for both peat and HA are showed in Fig. 2.

Amongst the nine PAHs analyzed in the peatsamples, seven of them were detected along theprofile (concentrations expressed as μg kg−1 dryweight), while Ace and InP were always below theLOD. In particular, Pyr, which averages around202.9 μg kg−1, was the predominant species in peatsamples, accounting for ca. 20–100% of the totalPAHs (sum of nine species, Σ PAHs) throughout theprofile. Phenanthrene and Flu (33.1 and 87.9 μg kg−1,average values) were found only in the first 30 cm ofdepth, while B[ghi]P, B[a]P, B[jbk]F and Fth weredetected “exclusively” between 28 and 31 cm ofdepth, although at different extents (i.e., 505.9, 199.5,29.4, and 80.0 μg kg−1, average values).

The Σ PAHs trend shows highest concentrationsbetween 20 and 30 cm of depth (1,051.9 μg kg−1,average value), with a clear peak of 1,265 μg kg−1 at29.6 cm of depth, corresponding to AD 1,919±6. Adramatic decrease in PAHs towards deeper peatregions (with an average of ca. 78 μg kg−1 between90 and 98 cm of depth) and a significant reductiontowards the peat surface (306.2 μg kg−1, averagevalue) were also observed (Fig. 3a).

The HA fraction along the profile represents 76.8 gkg−1 of the bulk peat in the first few centimetres ofdepth and the yield increases downcore to a maxi-mum of 324.0 g kg−1 (around 50–60 cm), indicativeof an increasing level of humification with depth.Although the HA extraction yields (EYHA=g HA/kg

dry peat) showed quite high values (246.5 g kg−1 inaverage) when compared with soil or sedimentsamples, the main problem occurred in PAHs deter-mination in HA was the “relatively” high LOD (ca.200 μg kg−1) due to the “relatively” low quantity ofhumic material recovered.

In fact, amongst the nine PAHs analyzed in the HAsamples, only Phe, and sporadically Pyr and Fth, weredetected throughout the profile. In particular, Pyr wasdetected only in the first few centimetres (250.4 and

687.2 μg kg−1 in the living layer and at 0.5 cm ofdepth, respectively), while Fth was detected in theliving layer (1,335.1 μg kg−1) and at 30 cm of depth(284.0 μg kg−1). On the contrary, Phe was observedin almost all HA samples and its concentration rangedbetween 2,011.8 μg kg−1, in the living layer, and210.3 μg kg−1 around 50–60 cm of depth, showing anaverage of 626.2 μg kg−1.

Discussion

PAHs temporal trends in peat

The Σ PAHs trend shows a large band between 36 cm(corresponding to the Industrial Revolution period)and 10 cm of depth (AD 1986). A clear peak (ca.1,250 μg kg−1) is appreciable at 28–30 cm of depth,corresponding to ca. AD 1920–1930 (Fig. 3a): in fact,between the 1920 and the 1940, the coal imports toSwitzerland reached their maximum levels (Müller1982) and an increasing of the industrial activityoccurred in the north-west of Italy. During theseyears, the estimated Σ PAHs deposition flux reachedvalues of 0.195 versus 0.027 mg m−2 year−1 duringthe first years of XXth century. Thus, the temporalchanges in Σ PAHs concentrations seem to beconsistent with the history of Swiss coal consump-tion, also according to Berset et al. (2001). In fact, Pb,As and S, elements which are commonly enriched incoals, show distribution patterns similar to PAHs,reaching their greatest concentrations (89.8±4.5, 7.0±1.5 and 1,967±187 μg g−1, respectively) at a depth of26–31 cm, which corresponds to the peak in totalPAHs (Fig. 3a). In addition, S concentrations aresignificantly correlated with Pb and As ones (R2=0.72and 0.64, respectively, p<0.001, n=91), thus con-firming similar main sources. Also the depositionfluxes of these elements seem to be consistent withthe Σ PAHs trend. In fact, all of them show anincrease since 1,828±20 (Industrial Revolution time)that reaches, during the years 1919–1940, valuesaveraging around 12.63±0.83 mg m−2 year−1 for Pb,0.97±0.16 mg m−2 year−1 for As, and 295.4±64.8 mgm−2 year−1 for S (Fig. 3b).

A dramatic decrease in PAHs towards deeper peatregions and a significant reduction towards the peatsurface were also observed. In detail, the presence ofPAHs (around 70 μg kg−1) in peat sample at 98 cm of

Plant Soil (2009) 315:35–45 41

depth (corresponding approx. at 2,040±70 14C yearBP) indicates mainly natural sources and could beassumed as background value, whereas the observedgeneral decrease in PAHs during the last decades canbe attributed to the substitution of coal as main energysource by hydroelectric power, natural gas, or nuclearpower, to the decline of heavy industry, and tosimultaneous improvements in emission controlmeasures for large scale combustion of fossil fuels(Sanders et al. 1995; Berset et al. 2001; Dreyer et al.2005). In fact, the Σ PAHs deposition flux estimatedfor the 1980–1990 period averaged around 0.080±0.019 mg m−2 y−1, that is ca. 2.5 times lower thanduring 1920–1930s.

As previously reported, Pyr is the major PAHsdetected throughout the bog profile, accounting foralmost 93–100% of total PAHs between 10 and 20 cmand below 35 cm of depth. If one plots the pyrogenicPAHs (Pyr + Fth + B[a]P + B[jbk]P + B[ghi]P) and theΣ PAHs trends vs. depths, they look very similar(R2=0.98, p<0.001, n=15), thus suggesting theburning of wood or coal as dominant source or,

below 36 cm of depth, as “exclusive” one. In the first8 cm and between 28 and 31 cm of depth, (i.e. thesection in which a peak in Σ PAHs occurs), pyrogenicPAHs account for 48–76% and 77–91% of total PAHs,respectively, suggesting additional anthropogenicsources of these organic contaminants (e.g., residentialheating, road traffic, industrial waste incinerators). Inparticular, in the upper 10 cm of the profile,corresponding to the 1990–2005 period, Phe and Fluaccount for 10–24 and 30–32% of Σ PAHs, respec-tively, thus giving a petrogenic contribute (Phe + Flu)that averages around 39%. These data could suggest asignificant release of uncombusted petroleum productssuch as unburned lubricating oils by road vehicleexhaust and/or spillages of petroleum and its refinedproducts. Actually, an unexpected Phe deposition fluxvalue of 0.044 mg m−2 year−1 was observed in theliving layer. Although there is no evidence for PAHsbiosynthesis by mosses (Galuszka 2007), that domi-nate the bog surface (Fig. 1), this result seems tosuggest a biogenic source (Phe production) besidescombustion processes (Flu and Pyr production).

0 200 400 600

1919

1828

2005

1901

1801

0 600 1200 1800 2400

1919

2005

1828

1961

0 2 4 6 8

1828

2005

19291919

1949

0 20 40 60 80 100

19191828

2005

1982

µg g -1 µg g-1 µg g -1

[Pb][As]

[S]

0,0 0,4 0,8 1,2 1,6

1919

1828

2005

1929

1945

1801

1901

-100

-80

-60

-40

-20

00 5 10 15

Dep

th (

cm)

1901

1828

2005

1919

1986

1801

1929

mg m-2 y-1mg m-2 y-1mg m-2 y-1

Pb depositionflux

As depositionflux

S depositionflux

b)

-100

-80

-60

-40

-20

00 350 700 1050

Dep

th (

cm) 1901

1828

2005

19191929

2040±70 14C yr BP

a)

PAHsPyr

µg kg-1

1400

Σ

1901

Fig. 3 Distribution of Σ PAHs, pyrene, Pb, As and S in peat samples (a) and corresponding deposition fluxes (b) along the 2T profile.210Pb age dating is reported in italic

42 Plant Soil (2009) 315:35–45

In conclusion, the total PAHs concentrationprofile seems to be generally consistent withchanges in organic contaminant emission, especial-ly deriving from coal utilization, thus supportingthe statement of ombrotrophic bogs as record ofatmospheric depositions. Results clearly show alsoa dominance of high molecular weight PAHs (fourto six rings), thus suggesting a significant pyrogen-ic origin, and that, among them, Pyr is the majorspecies detected throughout the profile, accountingfor 20–100% of Σ PAHs.

PAHs determination in HA

As reported above, amongst the nine PAHs analyzedin the HA samples, only Phe, and sporadically Pyrand Fth, were detected throughout the profile.

In particular, Phe was observed in almost all HAsamples and its concentration ranges between2,011.8 μg kg−1, in the living layer, and 210.3 μgkg−1 around 50–60 cm of depth. Plotting Pheconcentrations in HA against those in peat along thecore (Fig. 4), it is possible to observe a similarshape, especially in the upper part of the profile,with a main peak at 0.5 cm of depth that could berelated to a biogenic origin besides combustion

processes (Fernández et al. 1999). Although onlylimited data were obtained about all the studiedPAHs, results clearly show higher concentration ofPhe in HA rather than in bulk peat samples (626.2 vs26.4 μg kg−1, average values). Several mechanismshave been proposed about the “aging” of chemicalsin soils, including partitioning into or onto humicmatter (Chiou et al. 1979, 1983). In addition, Boganand Sullivan (2003) demonstrated that Phe in agingtests showed considerable evidence of sequestrationin soils and that its degradation decreases with theincrease of the organic matter content. Consequently,the sequestration of Phe in the stable, recalcitrant HAmolecules rather than in other compounds ofcorresponding peat samples could provide to Phe acertain “physico-chemical protection” against micro-bial degradation.

Compared to Phe, only a small fraction of Pyrseems to be sequestered by HA. In fact, expressingPyr concentrations in HA (when detected) as μg kg−1

of peat, this pollutant shows concentration values of18.9 and 52.0 μg kg−1peat, thus accounting for ca. 8–21% of total Pyr in peat.

Thus, HA play an important role in Phe persis-tence/binding in peat soils, while other PAH com-pounds, such as Phy, B[a]P and B[ghi]P, althoughoccurring at high concentrations in bulk peat, areprobably associated to different peat compounds, suchas humin (i.e., the insoluble fraction of HS) or non-humic substances (e.g., lipids), both removed duringHA isolation.

Although the procedure of fraction separationinvolves dissolution of HS in alkaline solution andacid precipitation to form HA aggregates, and thusone may argue that this procedure possibly produces achemical artefact or alters the existing distribution ofthese compounds, this study provides direct data onthe contribution of HA to the PAHs adsorption.Anyway, (i) the low solubility of PAHs in aqueoussolution, (ii) the similar Phe trend in both peat andHA along the profile, together with (iii) a commonmain peak in Phe, Pyr and Fth concentrations around0.5 cm of depth, seem to suggest a certain stratifica-tion of these pollutants, probably due to theirentrapment into the stable, recalcitrant HA fraction,rather then redistribution phenomena occurred duringHA isolation. Thus, given the physico-chemical andbiological stability of HA with time, they hold a mainrole in limiting the vertical migration of PAHs

0 700 1400 2100[Phe]HA (µg kg -1)

-100

-80

-60

-40

-20

0

0 20 40 60 80

[Phe]peat (µg kg -1)

Phe peat

Phe HA

Fig. 4 Distribution of Phe in peat (black line) andcorresponding HA (grey line) along the 2T profile

Plant Soil (2009) 315:35–45 43

throughout the profile, thus supporting the role ofombrotrophic bogs as proxy of hydrophobic organicpollutant atmospheric depositions during centuries, atleast at national or regional scale.

However, further investigations on physico-chem-ical adsorption and sequestration processes of PAHsby HA along undisturbed cores and on the possibleinfluence of extraction processes on PAHs distribu-tion will provide additional insights on the fate/behaviour of these widespread organic pollutants.

Acknowledgements The authors would like to gratefullyacknowledge Prof. W. Shotyk, University of Heidelberg, forproviding the peat samples and allowing XRF analysis in hisInstitute. Discussions with Prof. N. Senesi, Prof. M.D.R.Pizzigallo, University of Bari, and Dr. César Plaza, ConsejoSuperior de Investigaciones Científicas of Madrid, were helpfuland appreciated. We are grateful also to anonymous reviewersfor their valuable suggestions and critical comments on themanuscript.

References

Appleby PG, Oldfield F (1978) The calculation of lead-210 datesassuming a constant rate of supply of unsupported 210Pb tothe sediment. Catena 5:1–8. doi:10.1016/S0341-8162(78)80002-2

Appleby PG, Shotyk W, Fankhauser A (1997) Lead-210 agedating of three peat cores in the Jura Mountains, Switzer-land. Water Air Soil Pollut 100:223–231. doi:10.1023/A:1018380922280

Berset JD, Kuehne P, Shotyk W (2001) Concentrations anddistribution of some polychlorinated biphenyls (PCBs) andpolycyclic aromatic hydrocarbons (PAHs) in an ombro-trophic peat bog profile of Switzerland. Sci Total Environ267:67–85. doi:10.1016/S0048-9697(00)00763-4

Bogan BW, Sullivan WR (2003) Physicochemical soil parametersaffecting sequestration and mycobacterial biodegradation ofpolycyclic aromatic hydrocarbons in soil. Chemosphere52:1717–1726. doi:10.1016/S0045-6535(03)00455-7

Cheburkin AK, Shotyk W (1996) An energy-dispersive minip-robe multielement analyzer (EMMA) for direct analysis ofPb and other trace elements in peats. Fresenius J AnalChem 354:688–691

Chefetz B, Deshmukh AP, Hatcher PG, Guthrie EA (2000)Pyrene sorption by natural organic matter. Environ SciTechnol 34:2925–2930. doi:10.1021/es9912877

Chiou CT, Peters LJ, Freed VH (1979) A physical concept ofsoil–water equilibria for nonionic organic compounds.Science 206:831–832. doi:10.1126/science.206.4420.831

Chiou CT, Porter PE, Schmedding DW (1983) Partitionequilibria of nonionic organic compounds between soilorganic matter and water. Environ Sci Technol 17:227–231. doi:10.1021/es00110a009

Clymo RS (1983) Peat. In: Gore AJP (ed) Mires: swamp, bog,fen and moor, ecosystems of the world, 4A. Elsevier, NewYork, pp 159–224

Clymo RS (1984) The limits to peat bog growth. Philos Trans RSoc Lond Ser B 303:605–654. doi:10.1098/rstb.1984.0002

Cocozza C, D’Orazio V, Miano TM, Shotyk W (2003)Characterization of solid and aqueous phases of a peatbog profile using molecular fluorescence spectroscopy,ESR and FT-IR, and comparison with physical properties.Org Geochem 34:49–60. doi:10.1016/S0146-6380(02)00208-5

Conte P, Zena A, Pilidis G, Piccolo A (2001) Increasedretention of polycyclic aromatic hydrocarbons in soilsinduced by soil treatment with humic substances. EnvironPollut 112:27–31. doi:10.1016/S0269-7491(00)00101-9

Dahle S, Savinov VM, Matishov GG, Evenset A, Næs K(2003) Polycyclic aromatic hydrocarbons (PAHs) inbottom sediments of the Kara Sea shelf, Gulh of Ob andYenisei Bay. Sci Total Environ 306:57–71. doi:10.1016/S0048-9697(02)00484-9

Damman AWH (1978) Distribution and movement of elements inombrotrophic peat bogs. Oikos 30:480–495. doi:10.2307/3543344

Dreyer A, Radke M, Turunen J, Blodau C (2005) Long-termchange of polycyclic aromatic hydrocarbon deposition topeatlands of Eastern Canada. Environ Sci Technol39:3918–3924. doi:10.1021/es0481880

Feldmeyer-Christe E (1990) Etude phyto-écologique destourbières des Franches-Montagnes (canton du Jura et deBerne, Suisse). Matér levé géobot Suisse 66:163 pp

Fernández P, Vilanova RM, Grimalt JO (1999) Sediment fluxesof polycyclic aromatic hydrocarbons in European highaltitude mountain lakes. Environ Sci Technol 33:3716–3722. doi:10.1021/es9904639

Galuszka A (2007) Distribution patterns of PAHs and traceelements in mosses Hylocomium splendens (Hedw.) B.S.G. and Pleurozium schreberi (Brid.) Mitt. from differentforest communities: a case study, south-central Poland.Geoderma 67:1415–1422

IARC (International Agency for Research on Cancer) (1983)IARC monographs on the evaluation of the carcinogenicrisk of chemicals to human. Polynuclear aromatic com-pounds, Part I, Chemical, environmental, and experimentaldata. World Health Organization, Geneva, Switzerland

Johnson L, Damman AWH (1993) Decay and its regulation inSphagnum peatlands. In: Miller NG (ed) Advances inbryology, Band 5, Biology of Sphagnum, pp 249–296

Joray M (1942) L’Étange de la Gruyère, Jura bernois. Étudepollenanalytique et stratigraphique de la tourbière. In:Matériaux pour le levé géobotanique de la Suisse, 25.Hans Huber, Berne

Krauss M, Wilcke W, Martius C, Bandeira AG, Garcia MVB,Amelung W (2005) Atmospheric versus biological sourcesof polycyclic aromatic hydrocarbons (PAHs) in a tropicalrain forest environment. Environ Pollut 135:143–154.doi:10.1016/j.envpol.2004.09.012

Martínez-Cortizas A, Pontevedra-Pombal X, Garcia-Rodeja E,Novoa-Munoz JC, Shotyk W (1999) Mercury in aSpanish peat bog: archive of climate change andatmospheric metal deposition. Science 284:939–942.doi:10.1126/science.284.5416.939

44 Plant Soil (2009) 315:35–45

Moore P, Webb JA, Collinson ME (1991) Pollen analysis, 2ndedn. Blackwell Scientific, London, 216 pp

Müller K (1982) Die Bielerseesedimente 1878–1978. Ph.D.thesis, University of Berne

Nadal M, Schuhmacher M, Domingo JL (2004) Levels ofPAHs in soil and vegetation samples from TarragonaCounty, Spain. Environ Pollut 132:1–11. doi:10.1016/j.envpol.2004.04.003

Page DS, Boehm PD, Douglas GS, Bence AE, Burns WA,Mankiewicz PJ (1999) Pyrogenic polycyclic aromatichydrocarbons in sediments record past human activity: acase study in Prince William Sound, Alaska. Mar PollutBull 38:247–260. doi:10.1016/S0025-326X(98)00142-8

Pereira WE, Hostettler FD, Luoma SN, van Geen A, Fuller CC,Anima RJ (1999) Sedimentary record of anthropogenicand biogenic polycyclic aromatic hydrocarbons in SanFrancisco Bay, California. Mar Chem 64:99–113.doi:10.1016/S0304-4203(98)00087-5

Qiao M, Wang C, Huang S, Wang D, Wang Z (2006)Composition, sources, and potential toxicological signifi-cance of PAHs in the surface sediments of the MeiliangBay, Taihu Lake, China. Environ Int 32:28–33.doi:10.1016/j.envint.2005.04.005

Rapaport RA, Eisenreich SJ (1988) Historical atmosphericinputs of high molecular weight chlorinated hydrocarbonsto eastern North America. Environ Sci Technol 22:931–941. doi:10.1021/es00173a011

Robertson A (1998) Petroleum hydrocarbons. In AMAPassessment report: Arctic pollution issues. Arctic Moni-toring and Assessment Programme (AMAP), Oslo, Nor-way, pp 661–716

Sanders G, Jones KC, Hamilton-Taylor J, Dorr H (1995) PCBand PAH fluxes to a dated UK peat core. Environ Pollut89:17–25. doi:10.1016/0269-7491(94)00048-I

Senesi N, Miano TM (1995) The role of abiotic interaction withhumic substances on the environmental impact of organicpollutants. In: Huang PM, Berthelin J, Bollag JM, McGillWB, Page AL (eds) Environmental impact of soilcomponent interaction, natural and anthropogenic organ-ics. CRC Lewis, Boca Raton, pp 311–335

Shotyk W, Cheburkin AK, Appleby PG, Fankhauser A,Kramers JD (1996) Two thousand years of atmosphericarsenic, antimony, and lead deposition recorded in a peatbog profile, Jura Mountains, Switzerland. Earth Planet SciLett 145:1–7. doi:10.1016/S0012-821X(96)00197-5

Shotyk W, Weiss D, Appleby PG, Cheburkin AK, Frei R,Gloor M et al (1998) History of atmospheric leaddeposition since 12,370 14C yr BP from a peat bog, JuraMountains Switzerland. Science 281:1635–1640.doi:10.1126/science.281.5383.1635

Srogi K (2007) Monitoring of environmental exposure topolycyclic aromatic hydrocarbons: a review. EnvironChem Lett 5:169–195. doi:10.1007/s10311-007-0095-0

Stevenson FJ (1994) Humus chemistry. genesis, composition,reactions, 2nd edn. Wiley, New York

Swift RS (1996) Organic matter characterization. In: Sparks DLet al (ed) Methods of soil analysis. Part 3. Chemical methods.Soil Science Society of America book series 5. Soil ScienceSociety of America, Madison, WI, pp 1018–1020

Thiele-Bruhn S, Brümmer GW (2005) Kinetics of polycyclicaromatic hydrocarbon (PAH) degradation in long-termpolluted soils during bioremediation. Plant Soil 275:31–42.doi:10.1007/s11104-004-0265-9

van Geel B (1978) A palaeoecological study of Holocene peat bogsections in Germany and the Netherlands. Rev PalaeobotPalynol 25:1–120. doi:10.1016/0034-6667(78)90040-4

VenkatesanMI (1988) Occurrence and possible sources of perylenein marine sediments—a review. Mar Chem 25:1–17.doi:10.1016/0304-4203(88)90011-4

Wardenaar ECP (1987) A new hand tool for cutting peatprofiles. Can J Bot 65:1772–1773

Weber JH (1988) Binding and transport of metals by humicmaterials. In: Frimmel FH, Christman RF (eds) Humicsubstances and their role in the environment. Wiley,Chichester, UK, pp 165–178

Wilcke W (2000) Polycyclic aromatic hydrocarbons (PAHs) insoil—a review. J Plant Nutr Soil Sci 163:229–248.doi:10.1002/1522-2624(200006)163:3<229::AID-JPLN229>3.0.CO;2-6

Yang HH, Lee WJ, Chen SJ, Lai SO (1998) PAH emission fromvarious industrial stacks. J Hazard Mater 60:159–174.doi:10.1016/S0304-3894(98)00089-2

Yunker MB, Macdonald RW (2003) Alkane and PAH deposi-tional history, sources and fluxes in sediments from theFraser River Basin and Strait of Georgia, Canada. OrgGeochem 34:1429–1454. doi:10.1016/S0146-6380(03)00136-0

Zaccone C, Cocozza C, Cheburkin AK, Shotyk W, Miano TM(2007a) Highly organic soils as “Witnesses” of anthropo-genic Pb, Cu, Zn, and 137Cs inputs during centuries. WaterAir Soil Pollut 186:263–271. doi:10.1007/s11270-007-9482-1

Zaccone C, Miano TM, Shotyk W (2007b) Qualitativecomparison between raw peat and related humic acids inan ombrotrophic bog profile. Org Geochem 38:151–160.doi:10.1016/j.orggeochem.2006.06.023

Zaccone C, Cocozza C, D’Orazio V, Plaza C, Cheburkin AK,Miano TM (2007c) Influence of extractant on quality andtrace elements content of peat humic acids. Talanta73:820–830. doi:10.1016/j.talanta.2007.04.052

Zaccone C, Said-Pullicino D, Gigliotti G, Miano TM (2008a)Diagenetic trends in the phenolic constituents ofSphagnum-dominated peat and its corresponding humicacid fraction. Org Geochem 39:830–838. doi:10.1016/j.orggeochem.2008.04.018

Zaccone C, Cocozza C, Cheburkin AK, Shotyk W, Miano TM(2008b) Distribution of As, Cr, Ni, Rb, Ti and Zr betweenpeat and its humic fraction along an undisturbed ombro-trophic bog profile (NW Switzerland). Appl Geochem23:25–33. doi:10.1016/j.apgeochem.2007.09.002

Plant Soil (2009) 315:35–45 45