Evidence for Diffuse Contamination of River Sediments by Road

Mar 3, 2000 - Because of the intense road traffic in Alsace-Lorraine, main vehicle fuels and exhausts have been investigated. Unleaded and diesel fuel...
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Environ. Sci. Technol. 2000, 34, 1174-1181

Evidence for Diffuse Contamination of River Sediments by Road Asphalt Particles PIERRE FAURE,* PATRICK LANDAIS, LAURENCE SCHLEPP, AND RAYMOND MICHELS UMR 7566 G2R, “Ge´ologie et Gestion des Ressources Mine´rales et Energe´tiques”, and CREGU, Universite´ Henry Poincare´, BP 239, 54506 Vandoeuvre Le`s Nancy, Cedex, France

Saturated hydrocarbons analysis was carried out on different river sediments from Alsace-Lorraine in order to detect possible contaminations by petroleum byproducts. The distributions of n-alkanes from all studied samples are very similar and are characterized by an odd-over-even carbon number predominance, underlining the higher plant contributions. On the other hand, pentacyclic triterpanes and steranes occur in all river sediments and display similar signatures that are characteristic of a mature organic matter contribution inherited from anthropogenic contaminations. Among the different possible pollutants origins, point industrial sources seem unlikely because of the highly homogeneous biomarker signatures and the geographical repartition of the studied rivers. Because of the intense road traffic in Alsace-Lorraine, main vehicle fuels and exhausts have been investigated. Unleaded and diesel fuels, used engine oils, and engine exhausts cannot account for the biomarker distributions observed in river sediments. On the contrary, saturated hydrocarbons extracted from road asphalts are chiefly composed of polycyclic biomarkers with chromatographic signatures very close to those of river sediments. Moreover, microscopic investigations of river sediments allow us to identify asphalt particles and to confirm that the different rivers studied are contaminated by road asphalts. Such contaminations may distort biomarker signatures and GC-MS data and overprint the possible pollution by other petroleum byproducts.

Introduction The efficient identification of sources of contamination in natural environments is a major problem. It is then necessary to study specific markers which allow the major anthropogenic sources that are responsible for pollutions to be identified. Among organic pollutants, petroleum byproducts are often detected in marine environments (1, 2) as well as in continental systems (3-8). For example, approximately 750 000 ton of hydrocarbons is annually transported by rivers to the Mediterranean Sea (9). The ubiquity of most of the compounds involved in pollutions related to the petroleum byproducts requires investigations using adapted methodologies in order to tentatively identify the contaminant sources. For 40 years, petroleum organic geochemistry has developed analytical techniques and routines to study the fossil * Corresponding author telephone: 33 3 83 91 38 29; fax: 33 3 83 91 38 01; e-mail: [email protected]. 1174

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organic matter from sedimentary basins (10-12). The molecular analysis of extractable organic matter by gas chromatography-mass spectroscopy (GC-MS) is one of the main steps in fossil organic matter characterization. Numerous molecules or molecule families, named biological markers (or biomarkers), originating from living organisms have been identified in the fossil organic matter. Among the most frequently studied biomarkers, terpanes originate from bacteria lipidic membranes (procaryotes) (13). They correspond to bicyclic, tricyclic, tetracyclic, and pentacyclic compounds. The latter named hopanes (Figure 1a) are mostly formed from the C35 bacteriohopanepolyols that always constitute the major series in all hopanoid-producing bacteria (14, 15). Because of bacteria occurrence in all surface sediments, terpanes are frequently found in crude oils and kerogen extracts. Steranes (Figure 1b) that originate from sterols (16, 17) constituting the membrane of eucaryotic cells (18) are also frequently recorded in chromatographic analysis of fossil organic matter. All developed organisms (plankton, zooplankton, higher plants, or animals) contain relatively high amounts of sterols. As hopanes, steranes are ubiquitous because their precursors (sterols) are common in living organisms. Because of the relative chemical stability of their cyclic structure and their resistance toward biodegradation (19, 20), triterpanes and steranes are widely distributed in all sediments and often only slightly modified by diagenesis. They are therefore used as biomarkers to assess the maturation of a sediment (21, 22), for oil to source rock correlations (23-26), and for the tentative reconstruction of paleoenvironments (27-29). These two families of biomarkers (triterpanes and steranes) can also be used in the environmental field for characterizing petroleum byproduct contaminants encountered in polluted sites (30). These biomarkers are not affected by distillation processes, and their respective distributions remain unchanged (31). On the other hand, because polycyclic biomarkers are generally stable toward chemical and biological degradation processes, they still bear their source and maturity signatures after dissemination. Thus, the specific biomarker signatures should allow the petroleum pollutants encountered in polluted sites to be correlated to the source from which they are derived. The search for identical signatures from potential sources may help to reconstruct the pollution processes. Industrial activities in the Alsace-Lorraine region have been responsible for soils and rivers pollution. More specifically, coal extraction and processing, petroleum refining, and polymer manufacturing may constitute potential sources for sediments and soils contamination by organic pollutants. To evaluate the quality of river sediments, samples have been collected in different zones of the region. The aim of the present work is to characterize the saturated hydrocarbons extracted from the collected river sediments and to use the distribution of biomarkers in order to tentatively identify the main sources of organic pollution.

Experimental Section Samples. Different sediments coming from rivers of AlsaceLorraine (France) have been collected by the Water Agency Rhin-Meuse. The samples localization is shown in Figure 2. The watersheds drained by these different rivers and their respective flows (Table 1) are representative of the different river types generally encountered in Alsace-Lorraine: important rivers (Rhine, Moselle, Meurthe, Ill, and Meuse) and smaller ones (Rosselle, Fensch, Sarre, and Thur). 10.1021/es9909733 CCC: $19.00

 2000 American Chemical Society Published on Web 03/03/2000

FIGURE 1. (a) Pentacyclic triterpane and (b) sterane structures and (c) examples of different stereochemical isomarizations (r hydrogen atoms are below, and β hydrogen atoms are above the plane of the molecule, and R and S are the possible configurations of the asymmetric carbon atom). Extraction-Fractionation. The bitumen fraction was recovered by sediment extraction in a chloroform/methanol mixture (50/50) for 45 min at 60 °C. Asphaltene precipitation in pentane and liquid chromatography of the extracts on alumina and silica gel columns allowed the aliphatic hydrocarbons to be isolated (32). Blanks tests were carried out in order to confirm the absence of laboratory contaminants. Gas Chromatography-Mass Spectrometry (GC-MS). Aliphatic hydrocarbons were analyzed by GC-MS (HP 5890 series II GC coupled to a HP 5971 mass spectrometer), using an on-column injector, a 60 m DB-5 J&W, 0.25 mm i.d, 0.1 µm film fused silica column. The temperature program was from 60 to 130 °C at 15 °C/min and from 130 to 300 °C at 3 °C/min, followed by an isothermal stage at 300 °C for 15 min (constant helium flow of 1 mL/min). Electron impact mass spectra were achieved in both full-scan and single-ion monitoring (SIM). Mass fragmentograms of the fragments m/z ) 191 (hopanes) and m/z ) 217+218 (steranes) were recorded. Biomarkers were identified by examination of their mass spectra and their respective distributions and by comparison with published data (29, 31, 33-34).

Results and Discussion River Sediments. The saturated hydrocarbons of the different river sediments have been analyzed. Their distribution are very similar. The saturated hydrocarbon distributions of two river sediments (Ill and Meuse 1), which are representative of all the studied sediments, are shown in Figure 3, panels a1 and a2. They are characterized by the predominance of n-alkanes and by the occurrence of lower intensity peaks of polycyclic biomarkers. n-Alkanes. The distribution of the n-alkanes of river sediments show a marked odd-over-even predominance in the C24-C32 range. By way of comparison, the saturated hydrocarbon distributions of a typical forest soil mainly composed of beach leafs and resinous needles is shown in Figure 4. The n-alkanes odd predominance already observed in higher plant cuticular waxes (35) characterizes this sample. This suggests that all river sediments exhibit a major higher plant input. This is confirmed by microscopic observation of the sediments, which reveals that the organic fraction is almost exclusively constituted by seeds, leafs, and woody debris. Furthermore, information derived from flash pyrolysis GC-MS of the sediments (8) confirms the above statements as far as the pyrograms are dominated by methoxyphenols that are typical of lignin and degraded lignin contribution (36).

Polycyclic Biomarkers. The pentacyclic triterpane (m/z ) 191) and the sterane (m/z ) 217+218) distributions have been studied for all the samples. The pentacyclic triterpane distributions (m/z ) 191) of all the river sediments are very close and are characterized by the predominance of the 17R(H),21β(H)-30-norhopane and the 17R(H),21β(H)-hopane associated with the progressive decrease of homohopanes pairs with carbon number increase as shown in Figure 3, panels b1 and b2 (Table 3). All the pentacyclic triterpane distributions show the occurrence of gammacerane, which is generally observed in hypersaline sedimentary deposits (37). The presence of gammacerane underlines a common origin for the chloroform-soluble fraction of the organic matter. The hop(22)29-ene (a pentacyclic hopene) is also observed in most of the samples. This compound is typical of a biogenic input (38) and has already been observed in subaquatic recent sediments (ferns and procaryotes) (33, 39). The m/z ) 191 distribution of a reference sediment sampled in the upper waters of the Thur River (Figure 5, Table 3) is characterized by the single occurrence of this hop(22)29-ene. The biologically produced hopanes precursors carry a 22R configuration that is gradually converted to a mixture of 22R and 22S diastereoisomers (Figure 1c). The proportions of 22R and 22S can be calculated for all of the C31-C35 compounds (40, 41). The 22S/(22R+22S)- C31:C35 hopane ratios of the river sediments are shown in Table 2. Such values, which are similar for all samples, are characteristic of an organic material that has reached the oil window (29, 42). The sterane distributions (m/z ) 217+218) of the different samples exhibit the predominance of C27-C29 groups (Figure 3, panels c1 and c2, Table 4). A triangular diagram showing the relative proportions of the C27-C29 steranes is currently used to determine the environment of deposition of the organic matter (43, 44). In the triangular diagram shown in Figure 6, the river sediments group in the same zone of the diagram, thus suggesting a common origin for all the studied steranes. The isomerization of 5R(H),14R(H),17R(H),20R configuration (RRRR) inherited from living organisms is gradually converted during thermal maturation in other possible stereoisomers RRRS, RββS, and RββR until an equilibrium ratio is reached. The C29 sterane isomerization ratios 20S/(20S +20R) and ββ/(ββ+RR) (22, 44) increase progressively with maturity level until equilibrium values (0.52-0.55 and 0.670.71, respectively) (46). The diagram 20S/(20S+20R) versus ββ/(ββ+RR) C29 steranes of the river sediments is shown in Figure 7. The different samples show similar maturation levels as compared to the large scattering obtained when plotting in this diagram with different crude oils of variable maturity. The analysis of both pentacyclic triterpanes and steranes extracted from river sediments reveals: (i) very similar distributions of all the samples collected. The occurrence of a specific triterpane (gammacerane) as well as the relative proportions of C27-C29 steranes suggest a common organic source for these two families of biomarkers. (ii) the isomerization indices calculated on both steranes and pentacyclic triterpanes correspond to a thermal maturity level that is compatible with the oil genesis window, thus suggesting that they are derived from fossil organic matter. These two observations strongly suggest that all the studied river sediments have been contaminated by hydrocarbons derived from a similar type of organic matter. Petroleum Byproducts. To put forward a proposal that could explain the recorded contaminations, different hypothesis have been reviewed. The contribution of point source pollutions from petrochemical industries or refineries seems unlikely because of the homogeneous polycyclic biomarker signatures of all the river sediments. They can generate such biomarker distributions (8) but do not explain VOL. 34, NO. 7, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 2. Localization of the different river sediment samples.

TABLE 1. Identification, Localization of the Different Sediments Studied and River Watersheds Surface, Flow,a and Total Organic Carbon Contentb sample code

river

Thur

Thur

Rosselle Sarre Moselle1 Meurthe Ill Meuse 1 Moselle2 Moselle3 Meuse 2 Rhin

Rosselle Sarre Moselle Meurthe Ill Meuse Moselle Moselle Meuse Rhin

sample locality Barrage Kruth-Wildenstein Petite Rosselle Herbitzheim Bainville Bouxie` re-aux-Dames La Wantzenau Nouzonville Ars-sur-Moselle Moulins les Metz Revin Barrage d'Iffezheim

SBc (km2) 26.6 190 878 1 750 3 085 4 754 7 820 7 867 7 883 9 376 45 515

DBT 1/5 total org (m3/s) C (%) 0.425 1.3 1.8 6.9 8.5 28 20.4 18.8 18.8 23.8 510

ndd 8.5 2.3 1.9 1.5 5.2 4.4 2.4 2.2 4.9 1.5

a DBT 1/5: flow of low-water level find 1 year over 5. b Weight % of sediment. c SB, river watershed surface. d nd, not determined.

their occurrence in all the collected samples. Similarly, the absence of any pollution marker in the upper waters of the Thur River sediment (Figure 5, Table 3) collected far away from any road rules out any significant contribution of windblown dust or atmospheric organic contaminants. Then, it seems necessary to relate these contaminations to more diffuse sources. Among the different sites studied, the sediments sampled from the Thur River are interesting. As a matter of fact, the Thur River is located in a deep valley of the Vosges Mountains (glacial carved valley) mainly surrounded by coniferous and beech forests and devoid of any industrial activities (Figure 2). Contrary to the sample 1176

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collected upstream (Figure 5, Table 3), their chromatographic fingerprints bear the same characteristics as the other sediments and display the same terpane and sterane distributions. Then, it can be considered as a reference sample that can only be contaminated by road traffic-derived pollutants. The other studied sites are located in industrial developed zones and associated with an important road network. Vehicle traffic generates petroleum byproducts that may be taken into account in explaining the widespread contamination observed in the sampled sediments: Gasoline. The analysis of two different types of gasoline (unleaded and diesel fuel) by gas chromatography does not allow the identification of any biomarkers. These petroleum products correspond to light distillation fractions and do not contain heavy molecules as polycyclic biomarkers (47, 49). Used Engine Oil. Used engine oils of two vehicle types have been analyzed by GC-MS (unleaded and diesel engine) and show similar characteristics. The saturated hydrocarbon distributions of the unleaded fuel engine is shown in Figure 8, panel a1. It is characterized by an intense unresolved complex mixture (UCM) probably formed by iso- and cycloalkanes that are not separated in the chromatographic conditions used in this study (49) and by the occurrence of n-alkanes in the C22-C32 range without any predominance (Figure 8, panel a1, Tables 3 and 4). Some polycyclic biomarkers are observed in low abundance as shown in Figure 8, panels b1 and c1, but the yield of these compounds is very low as compared to the UCM. Their contribution to the polycyclic biomarkers observed in river sediments is unlikely because an intense UCM should also be observed in the

FIGURE 3. (a1 and a2) Saturated hydrocarbons, (b1 and b2) pentacyclic triterpanes (m/z ) 191), and (c1 and c2) steranes (m/z ) 217+218) distributions of the Ill and Meuse 1 River sediments (see identification in Tables 3 and 4).

FIGURE 5. Pentacyclic triterpanes (m/z ) 191) distributions of a reference sediment sampled in the upper waters of the Thur River. FIGURE 4. Saturated hydrocarbons distribution of beach leafs and resinous needles (full scan). river sediments chromatograms as well as even carbonnumbered n-alkanes. Furthermore, the dissemination of used engine oils may not account for such a widespread contamination.

Engine Exhausts. Numerous authors have studied engine exhausts (47, 50-52). Because they do not originate from gasoline or diesel fuels, pentacyclic triterpanes and steranes are introduced into the exhausts via the engine oil. However, the unresolved organic mixture (UCM) represents between 84.6% (catalyst-equipped autos) and 90.3% (heavy-duty diesel trucks) of the elutable organic mass (46). As for used engine VOL. 34, NO. 7, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 2. 22S/(22S+22R)-C31-C35 Hopanes Isomerization Ratios of River Sediments and Road Asphalts 22S/(22S+22R)-C31 hopanes

22S/(22S+22R)-C32 hopanes

22S/(22S+22R)-C33 hopanes

22S/(22S+22R)-C34 hopanes

22S/(22S+22R)-C35 hopanes

Thur Rosselle Sarre Moselle 1 Meurthe Ill Meuse 1 Moselle 2 Moselle 3 Meuse 2 Rhine

0.57 0.57 0.56 0.55 0.55 0.56 0.57 0.55 0.55 0.56 0.55

0.63 0.59 0.60 0.59 0.58 0.61 0.60 0.59 0.60 0.60 0.59

0.64 0.61 0.62 0.63 0.64 0.61 0.62 0.61 0.61 0.60 0.60

0.61 0.62 0.60 0.66 0.58 0.60 0.62 0.63 0.62 0.65 0.62

0.64 0.60 0.66 0.67 0.63 0.66 0.70 0.65 0.62 0.56 0.65

av SD

0.56 0.009

0.60 0.013

0.62 0.014

0.62 0.021

0.64 0.039

road asphalt 1 road asphalt 2 road asphalt 3

0.57 0.56 0.56

0.59 0.57 0.59

0.62 0.59 0.60

0.60 0.59 0.60

0.60 0.62 0.61

av SD

0.57 0.005

0.58 0.009

0.60 0.017

0.60 0.005

0.61 0.007

sample code

TABLE 3. Pentacyclic Triterpanes Identification in Chromatograms of Figure 3, Panels b1 and b2, and of Figure 7, Panels b1 and b2 symbol

name

carbon no.

1 2 3 4 5 6 7 G 8 9 10 11 12 13 14 15 H

18R(H)-22,29,30-trisnorhopane 17R(H)-22,29,30-trisnorneohopane 17R(H),21β(H)-30-norhopane 18R(H)-30-norneohopane 17R(H),21β(H)-hopane 22S-17R(H),21β(H)-30-homohopane 22R-17R(H),21β(H)-30-homohopane gammacerane 22S-17R(H),21β(H)-30-bishomohopane 22R-17R(H),21β(H)-30-bishomohopane 22S-17R(H),21β(H)-30-trishomohopane 22R-17R(H),21β(H)-30-trishomohopane 22S-17R(H),21β(H)-tetrakishomohopane 22R-17R(H),21β(H)-tetrakishomohopane 22S-17R(H),21β(H)-pentakishomohopane 22R-17R(H),21β(H)-pentakishomohopane hop(22)29-ene

C27 C27 C29 C29 C30 C31 C31 C30 C32 C32 C33 C33 C34 C34 C35 C35

FIGURE 6. Triangular diagram of the relative proportion of C27-C29 steranes of the different river sediments, road asphalts, and used engine oils.

TABLE 4. Sterane Identification in Chromatograms of Figure 3, Panels c1 and c2 symbol

name

carbon no.

1

5R(H),14β(H),17R(H)- + 5R(H),14R(H),17R(H)pregnane 5R(H),14β(H),17R(H)- + 5R(H),14R(H),17R(H)homopregnane 20S-5R(H),14R(H),17R(H)-cholestane 20R-5R(H),14β(H),17β(H)-cholestane 20S-5R(H),14β(H),17β(H)-cholestane 20R-5R(H),14R(H),17R(H)-cholestane 20S-5R(H),14R(H),17R(H)-24-methylcholestane 20R-5R(H),14β(H),17β(H)-24-methylcholestane 20S-5R(H),14β(H),17β(H)-24-methylcholestane 20R-5R(H),14R(H),17R(H)-24-methylcholestane 20S-5R(H),14R(H),17R(H)-24-ethylcholestane 20R-5R(H),14β(H),17β(H)-24-ethylcholestane 20S-5R(H),14β(H),17β(H)-24-ethylcholestane 20R-5R(H),14R(H),17R(H)-24-ethylcholestane

C21

2 3 4 5 6 7 8 9 10 11 12 13 14

C22 C27 C27 C27 C27 C28 C28 C28 C28 C29 C29 C29 C29

oil, the intense UCM of the exhausts may appear in the n-alkane distributions observed in river sediments, which is not the case. Thus, whatever their source, the different engine exhausts cannot explain the occurrence and the distribution of 1178

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FIGURE 7. 20rrrS/(20rrrS+20rrrR)-C29 sterane versus (ββ/ (ββ+rr)-C29 sterane diagram comparing a series of immature and mature crude oils with river sediments, road asphalts, and used engine oil. polycyclic biomarkers in the river sediments. On the other hand, Pieri et al. (31) have already studied the distribution of aliphatic compounds extracted from road asphalts and have shown that asphalt contains significant concentrations of polycyclic biomarkers. Road Asphalts. Three different road asphalts have been studied. They have been sampled in the vicinity of the Thur

FIGURE 8. (a1 and a2) Aliphatic (m/z ) 57), (b1 and b2) pentacyclic triterpanes (m/z ) 191), and (c1 and c2) steranes (m/z ) 217+218) distributions of a used engine oil and a road asphalt (see identification in Tables 3 and 4). River on two different roads. All these asphalts are totally extractable by chloroform and display similar characteristics that have been already recorded in other studies on road asphalts (31). A characteristic saturated hydrocarbon distribution of road asphalts is shown in Figure 8, panel a2. High amounts of pentacyclic triterpanes and steranes are observed while the UCM intensity remains limited (Figure 8, panels b2 and c2, Tables 3 and 4). On the other hand, n-alkanes are generally not observed (Figure 8, panel a2). The pentacyclic triterpane distributions of these asphalts are similar to the sediment ones. Especially, the specific pentacyclic triterpane (gammacerane) is observed in the three road asphalts. The 22S/(22R+22S)-C31:C35 hopane ratios calculated for the three road asphalts show values similar to those obtained for the river sediments (Table 2). The sterane distributions of road asphalts are very similar to those recorded from river sediments extracts. In the C27C29 steranes triangular diagram, the road asphalts plot in a part of the diagram which overlaps that of the river sediments (Figure 6). The diagram showing the plot of the C29 sterane isomerization ratios, 20S/(20S+20R) vs ββ/(ββ+RR) (Figure 7), indicates that the maturity level reached by the asphalts is very close to that deduced from the analysis of the steranes from the river sediments. It should also be pointed out that, as expected, used engine oil samples fall in the same region as road asphalts on Figures 6 and 7. Thus, the hopane and sterane distributions of road asphalts as well as used engine oil show similar characteristics

to those of river sediments. First, the deposition conditions parameters (occurrence of gammacerane, distribution of steranes in the C27-C29 triangular diagram) are similar. Second, the maturity indices based on isomerization ratios of hopanes and steranes show that road asphalts and used engine oil studied and river sediment contaminants have reached the same maturity level. On this basis, used engine oil as well as road asphalts can be considered as potential contaminants for the sediments analyzed in this work. However as already discussed, gas chromatograms of n-alkanes from the sediments do not exhibit any distribution that can be related to that of used engine oil (Figure 8). An intense biodegradation of the used oil engine could have removed these n-alkanes. However, this biodegradation must occur before the incorporation of the used engine oil in the sediment. Otherwise, the n-alkanes from the natural input should also be biodegraded. Furthermore, the intense biodegradation of the used engine oil should also induce some changes in the distribution of the steranes and hopanes (33) that is not observed in the present work. The alteration of the used engine oil on the road prior to incorporation into the sediment should be associated with an air oxidation. It has already been shown that such an alteration provokes the preferential alteration of the biomarkers (53), which is not observed in the different samples studied. Even if additional quantitative data should be available to confirm this hypothesis, it is strongly suggested that the specific biomarker distributions observed in all the VOL. 34, NO. 7, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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Literature Cited

FIGURE 9. Road asphalt particles in the coarse fraction (>620 µm) of the Thur River sediment (magnification ×8). river sediments studied may be inherited from road asphalt contamination. To understand the dispersion mode of road asphalt, the river sediments have been observed under microscope. In the coarse granulometric fraction (>620 µm) of the Thur sediments, asphalt particles have been identified (Figure 9). To confirm the origin of the particles, they have been impregnated with a drop of chloroform. The particles are quickly dissolved and replaced by a brown halo. In the others rivers, sediment particles are generally too small to be identified under an optical microscope. However, chloroform impregnation of these sediments allows a brown halo to be detected, thus suggesting the presence of small asphalt particles. On the contrary, the microscopic observation of the sediments does not allow us to detect impregnation figures related to oil pollution. Clearly, the contamination results in a particulate transport that can only be of concern, in this case road asphalt particles or particles resulting from the insolubilization of engine oil after severe surface alteration. In this last case, the observed particles should no longer be chloroform-soluble. Thus, the microscopic observations confirm the occurrence of a contamination by road asphalts with a predominant dispersion mode occurring as a solid phase. Such a type of diffuse contamination introduces an organic background in river sediments marked by the occurrence of polycyclic biomarkers. The characterization of specific petroleum byproducts in river sediments by using these biomarkers and the subsequent identification of the possible pollution sources are required to take into account this anthropic background that may occur in all industrialized zones. As a matter of fact, it may distort the interpretation of GC-MS data and overprint the message of other petroleum derivatives. Thus, detailed inspection of both the analytical data and the microscopic information should be carried out before establishing any pollutant source correlations for petroleum byproducts. Further studies are still needed in order to more precisely quantify the input of such contaminants and to evaluate their contribution to sediment anthropization.

Acknowledgments This research benefited from the financial support and the sampling capacities of the Agence de l’Eau Rhin-Meuse. P.F. was been supported by an MENRT doctoral grant and by a Region de Lorraine postdoctoral fellowship. We particularly acknowledge C. Breuzin and M. Babut of the Agence de l’Eau Rhin-Meuse for information concerning the different rivers studied and thoughtful discussions. 1180

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Received for review August 18, 1999. Revised manuscript received December 13, 1999. Accepted December 29, 1999. ES9909733

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