Rapid contamination screening of river sediments by flash pyrolysis-gas chromatography–mass spectrometry (PyGC–MS) and thermodesorption GC–MS (TdGC–MS)

Journal of Analytical and Applied Pyrolysis57 (2000) 187–202

Rapid contamination screening of riversediments by flash pyrolysis-gas

chromatography–mass spectrometry(PyGC–MS) and thermodesorption GC–MS

(TdGC–MS)

Pierre Faure *, Patrick LandaisUMR 7566 G2R, Uni6ersite Henry Poincare-Nancy I, BP239,

54506 Vandoeu6re les Nancy Cedex, France

Received 14 February 2000; accepted 4 July 2000

Abstract

For 20 years, pyrolysis-gas chromatography–mass spectrometry (PyGC–MS) has beencurrently used in order to improve the knowledge on recent (soils and sediments) and fossilcomplex organic matter. Actually, PyGC–MS is also proposed as a rapid tool for theinvestigation of different types of sediment contaminations. Such rapid investigations al-lowed to increase the number and the frequency of the controls of river sediments, which aregenerally time and money consuming. However, during flash pyrolysis, the moleculesgenerated derive from both macromolecules breakdown and thermovaporization of freecompounds. Then, a methodology allowing the fractionation of these two types of effluentsshould be developed. Two river sediments showing different contamination degrees havebeen investigated in order to test the different modes of pyrolysis. The efficiency ofthermodesorption-gas chromatography–mass spectrometry (TdGC–MS) at low temperature(300°C) for the study of free molecules (PAH, hydrocarbons, …) is compared with the resultsderived from traditional analysis (extraction, liquid chromatography and GC–MS). On theother hand, pyrolysis of pre-thermodesorbed sediments is carried out in order to analyze theresidual organic matter. However, the use of thermodesorption instead of solvent extractionfor free organic matter removal is not always efficient especially for high molecular masscompounds. On the other hand, although heavy molecular mass compounds are frequently

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188 P. Faure, P. Landais / J. Anal. Appl. Pyrolysis 57 (2001) 187–202

underestimated, the use of TdGC–MS remains an efficient tool for the rapid screening forcontaminant investigation. Moreover, low molecular mass organic compounds which aregenerally lost during traditional pre-treatment (extraction followed by reconcentration steps)are detected after thermodesorption of the raw sediment. © 2001 Elsevier Science B.V. Allrights reserved.

Keywords: Flash pyrolysis; Thermodesorption; Free and solid organic matter; PAH; Sediment

1. Introduction

Among the different pollutants encountered in river sediments, organic contami-nants may be abundant and diversified. Although the transportation of pollutantsdepends on their physical occurrences (dissolved, adsorbed or particulate), asignificant proportion remains trapped in river sediments. This accumulation ofpollutants in sediments allows their environmental impact on fauna and flora to betemporarily limited. However, during river flood, pollutants can be liberated inwater and may induce subsequent environmental troubles. As a matter of fact, theanalysis of river sediments is necessary in order to evaluate the risk of contamina-tion that may occur during river floods. In the Rhin-Meuse watersheds, the wateragency regularly controls the water quality and the sediments pollutions (herbicides,pesticides, polycyclic aromatic hydrocarbons (PAH)). However, as far as theclassical determination of pollution degrees in river sediments is time and moneyconsuming, the frequency and the spatial extension of the analytical tests remainlimited.

Flash pyrolysis coupled with gas chromatography–mass spectrometry (GC–MS)has been frequently used by geochemists and biologists in order to analyze thecomplex fractions of organic matter which are not directly separable by chromatog-raphy [1–3]. During flash pyrolysis, the organic matter is fragmented in smallentities, which can be subsequently separated by gas chromatography and analyzedby mass spectrometry or specific detectors. The identification can be carried outthanks to a rich databank of specific molecular markers from fossil organic matter[1,2,4–7] and recent organic matter in soils [3,8] or sediments [9–12]. In the mostfavorable cases, the molecular signature of the generated compounds allows thesources for natural and anthropic organic contributions to be identified.

Moreover, organic matter analysis by PyGC–MS that necessitates limited pre-treatments (freeze-drying), is fast and appears to be well adapted for the rapidexamination of sediment contaminations.

The organic characterization by PyGC–MS of global river sediments that allowsa rapid evaluation of the organic contamination degree has already been carried outby Kruge et al. (1998) [12] and Kruge (1999) [13]. However, the different com-pounds identified in the pyrograms are inherited from both the thermal breakdown

189P. Faure, P. Landais / J. Anal. Appl. Pyrolysis 57 (2001) 187–202

of complex macromolecules and the thermodesorption of free molecules [14].Pollutants, which present a major risk for the environment because they are mobileand bio-available, generally correspond to the thermodesorbable organic fraction.Besides this, the determination of solid state contaminants is also important inorder to obtain a more complete sketch of the environmental problems.

The aim of this paper is to compare the different ways of analyzing sedimentaryorganic matter using pyrolysis methodologies, (i) pyrolysis of the raw sediment; (ii)thermodesorption of the raw sediment followed by pyrolysis and (iii) pyrolysis ofthe pre-extracted sediment. In order to evaluate the efficiency of thermodesorptionfor free contaminants, the extracted hydrocarbons fractions (saturated and aro-matic) have also been analyzed.

2. Methods and materials

2.1. Samples

The Rhin-Meuse Water Agency has collected river sediments coming from tworivers of Alsace-Lorraine (France) during summer 1994. These rivers (Rosselle andFensch, see localization in Fig. 1) were chosen because of their high contaminationdegrees (intense industrial activities) already pointed out in preliminary studies [15].The watersheds drained by these different rivers and their respective flows areshown in Table 1.

2.2. Sample preparation

The river sediments were freeze-dried and crushed (B500 mm). An aliquot ofthese samples was extracted in hot chloroform during 45 min. In order to removethe chloroform, the sediments were dried at ambient temperature over night.

The aliphatic, aromatic and polar fractions were isolated by liquid chromatogra-phy on a silica column with successive elution by pentane and by a mixture ofpentane and dichloromethane. Polar compounds were recovered with methanol/dichloromethane.

2.3. Flash pyrolysis-gas chromatography–mass spectrometry (PyGC–MS)

Pyrolysis of raw freeze-dried and chloroform-extracted sediments were performedwith a CDS Analytical 2000 pyroprobe. Samples were loaded in quartz tubes andheated at 615°C during 15 s. The generated products were analyzed by gaschromatography–mass spectrometry (HP 5890 Serie II GC coupled to a HP 5971mass spectrometer), using a split–splitless injector, a 60 m DB-5 J & W, 0.25 mmi.d., 0.1 mm film fused silica column. After cryofocusing (−30°C), the GC oven wastemperature programmed from −30 to 40°C at 10°C min−1 and 40–300°C at 5°Cmin−1 following by a stage at 300°C during 10 min (constant helium flow of 1.4 mlmin−1).


2.4. Flash thermodesorption-gas chromatography–mass spectrometry (TdGC–MS)

The thermodesorption of freeze-dried sediments was carried out with the samepyrolyzer. Thermodesorption experiments have already been applied to recentsediments in order to study PAH contaminations [16]. Because of the PAHthermostability, the temperature used was 350°C. In this work, thermodesorptionexperiments were carried out at a lower temperature (300°C), which seems to be a

Fig. 1. Localization of the different river sediment samples.

Table 1Identification and localization of the two sediments studied and river watershed surface and flow (withSB, watershed surface and DBT 1/5:flow of low water level find 1 year over 5)

DBT 1/5 (m3 s−1)River Sample locality SB (km2)

3.5FlorangeFensch 831.3190Rosselle Petite Rosselle


Table 2TOC and chloroform extract yield (% of total sediment and of TOC) of the two rivers sediments

Extract (% TOC)TOC (%) Extract (% of total sediment)River

61.02.504.1Fensch8.4Rosselle 8.9 0.75

good compromise between a maximum thermodesorption efficiency and a mini-mum bonds alteration. The GC–MS characteristics and temperature program wereidentical to the pyrolysis procedure described above.

2.5. Gas chromatography–mass spectrometry (GC–MS)

Aliphatic and aromatic hydrocarbons dissolved in hexane (4 mg ml−1) wereanalyzed by gas chromatography–mass spectrometry (HP 5890 Serie II GC coupledto a HP 5972 mass spectrometer), using the same capillary column and temperatureprogram as described above.

2.6. Pyrograms, thermograms and chromatograms peaks identification

Compounds were identified based on their mass spectra and GC retention timewith reference to the Wiley and US National Bureau of Standards computerizedmass spectral libraries. The identifications were also based on comparisons withpublished mass spectra of pyrolysis compounds of proteins, polysaccharides lipids,lignins and fossil organic matter [1,5,8,17,18].

3. Results and discussion

3.1. Global parameters

Although the total organic carbon (TOC) of the Fensch river sediment is low(4.1%), the bitumen yield is very high (60% of TOC, Table 2). On the contrary, theRosselle sediment is characterized by a high TOC (8.9%) whereas its extract yieldis limited (8.4% of TOC).

3.2. Pyrolysis of raw sediments

The Rosselle sediment pyrogram (Fig. 2a) is marked by the predominance ofmono-aromatics (1, 5, 11 and 15), di-aromatics (21, 24, 28 and 32), carboxylic acids(4, 6, 44 and 48), methoxy-phenols (25, 26), dimethoxy-phenol (35) and phenoliccompounds (17 and 19, numerals in brackets indicate peak numbers in the differentchromatograms). Heavy molecular mass compounds are principally characterizedby the occurrence of n-alkanes (*) showing an odd over even predominance in theC25–C31 range.


The pyrogram of the Fensch sediment is very different (Fig. 2b). It is chieflycharacterized by the occurrence of aromatic hydrocarbons, benzene (1); toluene (5);styrene (14); methyl styrene (16) and PAH containing 2 (18, 21, 24, 27, 28, 29, 30,32, 33), 3 (38, 39, 42), 4 (45, 46, 49, 52, 53) and 4+ (54, 56, 57, 58, 59) benzenerings. Oxygen bearing PAH (36, 41, 43) and sulfur bearing PAH (37) are alsoobserved.

Interpreting the data extracted from these two sediment pyrograms in terms oforganic macromolecule nature and organic contamination remains difficult becausethe different chromatographic peaks identified in these pyrograms may originatefrom the combination of both the thermodesorbed compounds and the moleculesresulting from organic macromolecules breakdown.

For example, it is fundamental to know if the PAH observed in the Fensch riversediment are free, adsorbed on the mineral matrix (bio-available) or bound to thesedimentary organic macromolecules (trapped). Depending on their status (free ortrapped), the impact of these carcinogenic compounds will be drastically different.On the other hand, if solid organic matter characterization is requested, thedifferent compounds identified in the sediment pyrograms (particularly the Rosselleriver) must exclusively derive from the breakdown of the macromolecules.

Fig. 2. Pyrograms of Rosselle (a) and Fensch (b) rivers sediments pyrolysed at 615°C (cf. identificationin Table 4).


In order to bring these geochemical characterizations to a successful conclusion,it seems more adequate to analyze separately the thermodesorbable compounds andthose originating from the breakdown of macromolecules. Then, four differenttypes of analysis have been carried out, (i) thermodesorption of raw sedimentproviding thermodesorbable compounds; followed by (ii) a flash pyrolysis; (iii) apyrolysis of the pre-extracted sample in order to record the distribution of themolecules exclusively derived from the breakdown of organic macromolecules and(iv) the direct injection of extracted hydrocarbons (aromatic and saturated). Thecomparison between thermodesorbed molecules and extracted hydrocarbons allowto evaluate the efficiency of thermodesorption for a rapid investigation of mobilecompounds. On the other hand, in order to avoid the extraction step generallycarried out before investigating solid organic matter, pre-thermodesorbed andpre-extracted sediment pyrograms are compared so as to examine the ability ofthermodesorption to totally remove free molecules.

3.3. Thermodesorption of raw sediments

The chromatogram of the Rosselle sediment obtained after thermodesorption(i.e. thermogram, Fig. 3a) is close to the pyrogram of the raw sediment (Fig. 2a).However, it is characterized by a lower abundance of heavy molecular masscompounds. As a matter of fact, the major compounds already identified in thepyrogram of the Rosselle sediment (Fig. 2a), especially alkyl-benzenes (5, 11, 15),naphthalene (21), alkyl-naphthalenes (24, 28), are desorbable molecules and notmacromolecules breakdown fragments. On the contrary, the methoxy-phenols (25,26, 35) observed in the pyrogram (Fig. 2a) are absent in the thermogram thussuggesting that these compounds derive from the breakdown of organicmacromolecules.

The pyrogram of the raw sample (Fig. 2a) does not allow the information on theorganic macromolecular structure to be obtained because the different moleculesinherited from the breakdown of macromolecules are partially masked by thethermodesorbable molecules. It is then necessary to first release the thermodes-orbable fraction in order to tentatively obtain informations on the organic macro-molecular structure. On the other hand, thermodesorption provides informations,which are generally deduced from the analysis of extractable fractions obtainedafter extraction and liquid chromatography. For example, the odd predominance ofheavy n-alkanes noticed in the pyrogram (Fig. 2a) is also observed in the ther-mogram (Fig. 3a).

n-Alkanes and isoprenoids (pristane and phytane) distribution extracted from thethermogram (m/z=57, Fig. 4a) confirms the predominance of odd over even heavyn-alkanes. This distribution is characterized by the preponderance of low molecularmass n-alkanes. The distribution of n-alkanes obtained from extracted saturatedhydrocarbons (Fig. 4b) is devoid of light n-alkanes suggesting a loss of these latterby evaporation during extraction and fractionation treatments. On the contrary, thepredominance of heavy molecular mass n-alkanes in extracted saturated hydrocar-bons underline that thermodesorption temperature (300°C) is not high enough to


Fig. 3. Thermograms of Rosselle (a) and Fensch (b) rivers sediments thermodesorbed at 300°C (cf.identification in Table 4).

vaporize heavy mass molecules (C\27). Such a specific signature (odd heavyn-alkanes predominance) generally encountered in aliphatic hydrocarbons isolatedby liquid chromatography characterizes the contribution of higher plants cuticularwaxes [19].

The pristane/nC17, phytane/nC18 and pristane/phytane ratios (Table 3) deducedfrom the extracted and thermodesorbed n-alkanes are very similar and can becalculated in thermograms as well as saturates chromatograms (Table 4).

The thermogram of the Fensch river sediment (Fig. 3b) is very similar to thepyrogram of the raw sediment (Fig. 2b). Aromatic hydrocarbons and especiallyPAH are the predominant compounds desorbed at 300°C. However, due to thethermodesorption temperature, the heaviest molecular mass PAH (54, 56, 57, 58,59) are less abundant or absent. Similarly, the absence of the low molecular masscompounds (1, 2, 5, 9, 10, 11, 14, 16) observed in the pyrogram of Fig. 2b probablyindicates that they originate from bonds breakdown of complex macromolecules.

The distribution of aromatic hydrocarbons extracted and isolated by liquidchromatography (Fig. 5) is very close to the corresponding thermogram (Fig. 3b).However, the heavy molecular mass PAH (54, 56, 57, 58) are clearly more


abundant in the extracted fraction. As observed for n-alkanes distribution in theRosselle sediment, the thermodesorption temperature (300°C) does not allow freeheavy molecules to be released.

The free PAH predominance in the pyrogram of the Fensch river (Fig. 2b) isconsistent with the high chloroform extraction yield (60%) calculated for the Fenschsediment. Such PAH mainly derive from two types of anthropic sources, (i)petrogenetic source (inherited from crude oil contamination) or (ii) pyrogeneticorigin (inherited from petroleum and coal combustion byproducts) [20]. The PAHdistribution of the Fensch river sediment does not allow to conclude on their originalthough the relative high proportion of substituted-PAH may underline a petroge-netic origin [21].

In terms of contamination screening, such results underline the necessity for athermodesorption step which allows to reveal organic contaminations that can besubsequently analyzed in detail using standard analyses (extraction, liquid chro-matography, gas chromatography, …). Moreover, thermodesorption allows to

Fig. 4. n-Alkanes and isoprenoids distribution (m/z=57) of Rosselle river sediments (a) after thermod-esorption at 300°C and (b) from extracted saturated hydrocarbons (axis numeral indicates the n-alkanescarbon number).

Table 3Pristane/nC17, phytane/nC18 and pristane/phytane ratios deduced from extracted and thermodesorbedhydrocarbons distributions of the Rosselle sediment

Pristane/phytanePristane/nC17 Phytane/nC18

Extracted hydrocarbons 1.56 0.55 3.423.150.57Thermodesorbed hydrocarbons 1.51


Table 4Identification of compounds recorded in the different chromatograms

MW (g mol−1)CompoundsNumber

Benzene1 782 84Thiophene3 C1-cyclohexane 98

604 Ethanoic acid92Toluene (C1-benzene)5

Propanoic acid 746112C2-cyclohexane7

888 Butanoic acid96Furancarboxaldehyde9

10 C1-pyrrole 81106C2-benzene11102Pentanoic acid12116Hexanoic acid13104Styrene14

C3-benzene 1201511816 C1-styrene

94Phenol17Indene 11618

10819 C1-phenol122C2-phenol20

Naphtalene 12821C1-methoxy-phenol (methyl-guaiacol) 13822

152C2-methoxy-phenol (ethyl-guaiacol)23142C1-naphtalene2415025 Vinyl-methoxy-phenol164C3-methoxy-phenol (isoeugenol)26154Byphenyl27156C2-naphtalene28

Acenaphtylene 1522915430 Acenaphtene168Dibenzofuran31

C3-naphtalene 1703216633 Fluorene182C1-dibenzofuran34

C3-dimethoxy-phenol (methoxyeugenol) 19435Fluorenone 18036

184Dibenzothiophene3738 Phenanthrene 178

178Anthracene39228Tetradecanoic acid40

Anthracenone 19441192C1-phenanthrene4220843 Anthacenedione256Hexadecanoic acid44

45 Fluoranthene 20220246 Pyrene218Benzonapthofurane47

Octadecanoic acid 2844849 216C1-pyrene and C1-fluoranthene


Table 4 (Continued)

CompoundsNumber MW (g mol−1)

50 Benzo[de]anthracenone 230Benzonapthothiophene 23451

52 228Benzo[a]anthraceneChrysene 22853Benzo-[b] & [k] fluoranthenes 25254

370Biomarker (cholestene)5556 Benzo[e]pyrene 25257 Benzo[a]pyrene 252

PAH of 276 and 278 g mol−158 276–278PAH of 300 and 302 g mol−159 300–302* n-Alkanes n-Alkenes

characterize lighter compounds (such n-alkanes) which are generally lost by evapo-ration during samples pre-treatments. On the contrary, heavy molecular masscompounds are only partially or nondesorbed at 300°C. Also, the combination ofthermodesorption with chloroform extract analysis allows to carry out a fullmolecular characterization of the free organic fraction containing light and heavymolecular compounds. On the other hand, thermodesorption may be first used forthe rapid screening of contaminants. However, when a contamination is pointedout, extract analysis must be carried out in order to avoid the heavy molecular massmoieties underestimation.

Fig. 5. Chromatogram of the extracted aromatic hydrocarbons of the Fensch river sediments (cf.identification in Table 4).


Fig. 6. Pyrogams of Rosselle (a) and Fensch (b) rivers sediments after thermodesorption at 300°C (cf.identification in Table 4).

3.4. Pyrolysis of raw sediments after thermo-desorption

In order to study the only contribution of solid organic matter in terms ofcontamination evaluation or structural determination, it is first necessary to removethe free organic fraction either by organic solvent extraction or by thermodesorp-tion. The comparison between thermodesorbed sediment and pre-extracted sedi-ments pyrolysates was carried out in order to discuss the efficiency of eachpreparative technique.

The pre-thermodesorbed Rosselle sediment pyrogram (Fig. 6a) is characterizedby a large variety of compounds. Among these different compounds, the majorspecific source markers correspond to the methoxy-phenol group (22, 23, 25, 26,35). These latter were already observed in the raw sediment pyrolysate but in lowerproportion. They are the typical pyrolysis products of lignin and degraded lignin[22] underlining terrestrial plant inputs. On the contrary, carboxylic acids (40, 44,48) which are inherited from lipids, originates from a large variety of organisms(higher plants, fungi and bacteria) containing these fatty acids [22]. Phenol andalkyl-phenols (17, 19, 20) are also relatively ubiquitous in pyrolysates. They can


derive from natural sources such as higher plants-derived products (pine needles,leafs, seeds) [23], lignin-derived products [22], marine organic matter [10,24] fossilorganic matter (coal, kerogen) [1,15] and industrial byproducts (coke residue) [15].On the other hand, mono-aromatic hydrocarbons (1, 5, 11), which correspond tolow molecular mass compounds, result from extensive thermal degradation ofindividual amino-acids, lignins [3], humic acids [25], kerogen and coal [1,15].

The pyrogram of the Fensch river sediment (Fig. 6b) shows a very highproportion of heavy molecular mass PAH (52, 53, 54, 56, 57, 58, 59). Thesecompounds because of their high vaporization temperature, were not desorbed at300°C and are probably desorbed during the pyrolysis carried out at 615°C. Forexample, the boiling point temperatures of chrysene (228 g mol−1), benzo(a)pyrene(252 g mol−1), dibenzo(a,h)anthracene (278 g mol−1) and coronene (300 g mol−1)are, respectively, 448, 495, 524 and 525°C. On the other hand, low molecular masscompounds such as aromatic (benzene, toluene, styrene) and oxygenated moieties(furancarboxaldehyde, phenol, C1-phenol) are observed. These compounds may beinherited from the breakdown of more complex organic molecules.

Fig. 7. Pyrogams of pre-extracted Rosselle (a) and Fensch (b) rivers sediments (cf. identification in Table4).


3.5. Pyrolysis of pre-extracted sediments

The pyrogram of the pre-extracted Rosselle sediment (Fig. 7a) is very close to thepyrogram obtained after thermodesorption (Fig. 6a). Such a result underlines theefficiency of thermodesorption to remove extractable compounds. Indeed, in thecase of the Rosselle river sediment, the free compounds show a limited molecularmass range implying a good efficiency of the thermodesorption at 300°C.

During pyrolysis, the Fensch river pre-extracted sediment (Fig. 7b) chieflygenerates PAH. It is difficult to determine if they come from the breakdown oforganic macromolecules or if they derive from residual molecules, which were notextracted. However, the absence of other organic compounds produced during theflash pyrolysis underlines a very low solid organic contribution in the Fensch riverwhich is confirmed by the low TOC value of this sample (Table 2). The proportionof low molecular mass compounds (5, 14, ) in the pre-extracted sample pyrogram(Fig. 7b) is clearly lower than in the pre-desorbed sample (Fig. 6b). It is suggestedthat these compounds are inherited from the breakdown of heavy PAH, which areabundant in the pre-thermodesorbed sample pyrogram (Fig. 6b). In this latter case,thermodesorption is not efficient to remove the compounds corresponding to theextractable organic matter.

4. Conclusion

Flash pyrolysis coupled with gas chromatography–mass spectrometry (PyGC–MS) has been applied to different river sediments in order to carry out the rapidinvestigation of organic pollutions. However, the major problem in the flashpyrolysis process results from contributions of both the thermovaporizablemolecules and the compounds inherited from macromolecules breakdown. The aimof this paper was to present different types of PyGC–MS applications allowing todeal with the rapid characterization of free contaminations and on the other handwith solid organic matter including natural and anthropic inputs.

Thermodesorption is an efficient step for the rapid determination of sedimentcontamination by free pollutants (especially for PAH) and can provide fundamentalinformations to environmental agencies for long term management of rivers andsediments.

However, heavy molecular mass molecules are not vaporizable at the thermodes-orption temperature used (300°C) implying an under-estimation of heavy contami-nants contribution. When such contaminations are detected, it is also necessary tocomplete the analytical scheme by using more conventional techniques (extraction,liquid chromatography, …). On the other hand, thermodesorption allows topreserve low molecular mass compounds, which are generally lost during tradi-tional pre-treatments.

In term of macromolecular characterization, thermodesorption before pyrolysis isnot always able to totally remove free molecules. Organic solvent extractionsremain the more efficient step to facilitate the examination of the solid residual


phases. The pyrolysis of pre-extracted sample provide information about the sourceof particulate organic matter, autochthonous (algae and bacteria) or allochthonousinputs which can be natural (soil fauna and higher plants) and anthropic (coal, cokedeposit, plastic byproducts, …).

In order to improve the pollution screening quantitative data are strongly needed.The use of an appropriate standard as proposed by Kruge (1999) [13] may allowquantitative data to be obtained. On the other hand, calibrated specific detectorssuch as flame ionization detector (FID) or atomic emission detector (AED) canprovide quantitative data and also allow to determine contamination degrees.Additional information can also be obtained when determining the weight loss afterthe different thermal treatments (thermodesorption, pyrolysis) and comparing thesequantitative data with those derived from solvent extraction of the sediments andfractionation of the extracts.

Acknowledgements

The authors acknowledge the ‘Agence de l’Eau Rhin-Meuse’ and particularly M.Babut for providing the sample of Fensch and Rosselle rivers sediments.

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Rapid contamination screening of river sediments by flash pyrolysis-gas chromatography–mass spectrometry (PyGC–MS) and thermodesorption GC–MS (TdGC–MS)