Oxygen

Environ. Sci. Technol. 1996, 30, 2495-2503

Aliphatic and Polycyclic Aromatic Hydrocarbons and Sulfur/Oxygen Derivatives in Northwestern Mediterranean Sediments: Spatial and Temporal Variability, Fluxes, and Budgets IMMACULADA TOLOSA,† JOSEP M. BAYONA, AND J O A N A L B A I G EÄ S * Environmental Chemistry Department, Centro de Investigacioń y Desarrollo (C.S.I.C.), Jordi Girona 18-26, E-08034 Barcelona, Spain

The spatial and temporal distribution of aliphatic and polycyclic aromatic hydrocarbons (PAHs) and sulfur/oxygen derivatives in sediments from the NW Mediterranean basin were investigated. Along the Continental Shelf and slope, an unresolved complex mixture (UCM) of aliphatic hydrocarbons and alkylated PAHs, indicative of petrogenic inputs, were predominant. Long-chain n-alkanes derived from terrestrial plant waxes (n-C27, n-C29, and n-C31) and parent PAHs, which are typical of high-temperature combustion processes, were evenly distributed in the whole basin and largely prevailing in the deepest areas. Perylene, a geochemically derived PAH, was found highly abundant in the areas influenced by river discharges. The highest anthropogenic hydrocarbon inputs were found near the cities of Marseille and Barcelona, being the contribution of the Rhone River ca. 25 times higher than that of the Ebro. Fluxes of PAHs in the deep basin were consistent with a predominant atmospheric input. These results account for an accumulation rate in the NW Mediterranean sediments of 2700 t/year of petrogenic unresolved hydrocarbons (UCM) and 60 t/year of pyrolytic PAHs. Analyses of dated sediment cores from the Rhone and Ebro prodeltas exhibited maximum accumulation rates of PAHs in the 1920-1940 and the 1975-1990 periods, although with a steep decrease since 1985 in the Rhone area.

Introduction The NW Mediterranean Sea is a subbasin of the Mediterranean that covers a surface of 280 000 km2 (Figure 1) with * Corresponding author fax: 34-3-2045904; e-mail address: [email protected]. † Present address: IAEA Marine Environment Laboratory, B.P. 800, MC-98012 Monaco.

S0013-936X(95)00647-X CCC: $12.00

 1996 American Chemical Society

a maximum depth of 2800 m (1). The average salinity is relatively high (38.5‰) due to the low freshwater inputs and to the high evaporation rates of water, which is compensated for with a net influx of lower salinity Atlantic surface water. The implication of these hydrogeographical features in the accumulation of land-based contaminants, and particularly hydrocarbons in the basin, has deserved a major concern and prompted the adoption of a specific protocol within the Barcelona Convention for the protection of the Mediterranean. In fact, the basin receives extensive discharges from the surrounding industrialized countries, particularly through the Rhone and Ebro Rivers, with average flow rates of 1710 and 250 m3/s, respectively. Barcelona and Marseille with 2.5 and 1.0 million inhabitants, respectively, are the main coastal urban centers that discharge their primary treated wastewaters onto the Continental Shelf through submarine outfalls. Coastal sewage dumping, continental runoff, river outflows, and accidental oil spills are the expected contributors of hydrocarbons to this marine region. These anthropogenic sources merge together with natural inputs, such as terrestrial plant waxes and marine phytoplankton, biomass combustion, and diagenetically produced aromatic compounds from biogenic precursors (2). Atmospheric deposition, including both natural and anthropogenic hydrocarbons, may also contribute to the marine hydrocarbon budget (3). These sources and the physicochemical properties of the individual components determine the species present in the different marine compartments and their ultimate fate. In this respect, their transport and accumulation to bottom sediments through the association with fecal pellets and rapidly sinking particles are significant processes of removal from the water column (4). The use of several molecular markers and related indices derived for n-alkanes (5) and PAHs (6) has been proposed for assessing the relative contributions to the environment of hydrocarbon sources, namely, biogenic, diagenetic, petrogenic, and pyrogenic (7). In this paper, we have used these concepts to assess the spatial and temporal variability of hydrocarbons in sediments from the NW Mediterranean and the importance of the latter as a sink for these compounds. Although the literature on sedimentary hydrocarbons in this region is rather abundant, it is largely focused on coastal areas (8-15), and no data are available for the whole basin. Therefore, in this work a special attention was focused in areas reflecting both the potential point sources, such as the Rhone and Ebro deltas and the Continental Shelf, and the end-members of the transport and depositional pathways, such as the continental slope and the deep basin. Data on fluxes and budgets are also relevant for constructing a hydrocarbon mass balance to better interpret the impact of pollution in this particular area. These have been computed from 210Pb-dated sediments. Furthermore, two dated cores from the Ebro and Rhone prodeltas were analyzed to find out the historical trends of the hydrocarbon inputs in the area.

Experimental Section Sampling. Sediments from water column depths ranging from 11 to 2700 m at the stations indicated in Figure 1 were

VOL. 30, NO. 8, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. Area of study and sampling site locations.

box-cored during several oceanographic cruises (from 1987 to 1991). The geographical coordinates of these sites, sample characteristics, and sampling procedure are described in detail elsewhere (16). Briefly, subsamples were obtained with a stainless steel tubing (6 cm i.d. × 40 cm long) provided with PTFE stoppers. Simultaneously, surface sediment (1 cm) was taken with a metallic spatula and stored in a cleaned jar. Samples were frozen at -20 °C immediately after collection and stored in vertical position to avoid mixing of the soft top layer during transportation. Geochronological (210Pb) data were obtained on subsamples obtained with a PVC pipe (6 cm i.d; 30 cm length) (17, 18). Further details about sedimentation and mixing rates have also been reported (16). Materials. Squalane, n-C14, n-C22, n-C32, n-C36, perdeuterated pyrene, anthracene, fluoranthene, chrysene, benzo[a]pyrene, and benzo[ghi]perylene were obtained from Fluka (Buchs, Switzerland). All solvents used were of pesticide grade or better. Diethyl ether was obtained from Carlo Erba Farmitalia (Milan, Italy). n-Hexane, methanol, and dichloromethane were purchased from Scharlau (Barcelona, Spain). Florisil (60-100 mesh), sodium sulfate and isooctane were obtained from Merck (Darmstadt, Germany). Analytical Procedures. Freeze-dried sediments (10 g) were spiked with squalane (1.3-8.8 µg) and perdeuterated pyrene (7-1000 ng) as analyte surrogates for aliphatic and aromatic hydrocarbons, respectively. Spiked sediments were Soxhlet extracted with dichloromethane/methanol (2: 1) for 36 h. Organic extracts were concentrated to 0.5-1 mL in a rotary evaporator, adsorbed onto 2 g of anhydrous sodium sulfate, and dried under a gentle stream of nitrogen.

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The adsorbed organic extracts were transferred on top of a glass column (35 cm × 0.9 i.d.) packed with 5 g of activated (120 °C) Florisil. The following fractions were collected: F-I, 40 mL of n-hexane (aliphatic hydrocarbons); F-II, 20 mL of 10% diethyl ether in n-hexane (aromatic hydrocarbons from two to four aromatic rings and dibenzothiophenes derivatives); F-III, 50 mL of 25% diethyl ether in n-hexane (aromatic hydrocarbons with more than four aromatic rings and sulfur/oxygenated PAHs derivatives). Recoveries for the overall procedure carried out with spiked sediments were higher than 80% with RSD below 20% (n ) 5). The aliphatic fraction (F-I) was analyzed by capillary GC-FID using a Fisons 5300 GC equipped with an AS 200 autosampler. Samples were injected in the splitless mode at 300 °C, and the detector temperature was held at 330 °C. A bonded 5% diphenyl dimethyl polysiloxane (DB-5) coated (0.25 µm thickness) on a 30 m × 0.25 mm i.d. fused silica capillary column (J&W Scientific, Folsom, CA) was used. The oven temperature was programmed from 60 to 310 °C at 6 °C/min and kept at 310 °C for 15 min. Hydrogen was the carrier gas at 2 mL/min. Peak and UCM areas were measured using a Nelson data acquisition system (Perkin-Elmer). Quantitation of n-alkanes was based on an external calibration mixture containing n-C14, n-C22, n-C32, and n-C36 according with the response factor of the closest eluting compound. On the other hand, the response factor applied for the UCM quantitation was the same so that the external standard eluted in its maximum abundance. Results were corrected by surrogate recoveries. Confirmatory analyses were performed by gas chromatography/mass spectrometry (GC/

MS) scanning from 40 to 550 amu every second under the analytical conditions indicated below. The aromatic fraction was analyzed by GC/MS using a Hewlett-Packard 5995 with a HP 300 data acquisition system. Electron impact (EI) mass spectra were obtained at 70 eV at ionization energy. Helium was the carrier gas at 30 cm/s. Temperatures were as follows: injector 300 °C, transfer line 300 °C, ion source 180 °C, and analyzer 230 °C. PAH analyses were performed in the selected ion monitoring mode according to the following acquisition program: m/z 178, 184, 192, 198, 206, 202, 216, 218, 226, 228, 234, 252, 276, 278, 300, and 302 (dwell time of 50 ms per single ion). Identification of the individual PAHs has been achieved by co-injection of standards, by diagnostic ion matching against molecular ion, and by comparison of retention indices with those obtained from the literature (19, 20). The concentrations of individual PAHs were obtained by external standard quantitation (anthracene, 178; fluoranthene, 202; pyrene-d10, 212; chrysene, 228; benzo[a]pyrene, 252; benzo[ghi]perylene, 276) using the response factor of the standard exhibiting the closest retention index. Reported concentrations are corrected for surrogate recoveries. The identification of polycyclic aromatic ketones and quinones was performed by negative ion chemical ionization (NICI) GC/MS in an INCOS-50 Finnigan instrument. The chromatographic conditions were identical to those described above for EI-GC/MS. The ion source and mass analyzer were held at 120 °C. Methane was used as the reagent gas at 0.055 Torr in the analyzer. A tentative identification of these compounds was done by comparing the mass spectra with those previously reported (21, 22).

Results and Discussion Aliphatic Hydrocarbons. The aliphatic hydrocarbon fraction of the NW Mediterranean surficial sediments showed variable distributions of resolved components overlying an unresolved complex mixture (UCM) of hydrocarbons. Representative GC profiles are illustrated in Figure 2. Among the resolved components, the n-alkanes were the most prominent. Marine phytoplanktonic hydrocarbons characterized by low odd carbon numbered n-alkanes (nC15 and n-C17) were identified only as trace constituents in sediments from the Continental Shelf (mainly in the river mouths). Conversely, the long-chain n-alkane homologs (n-C27, n-C29, and n-C31), derived from epicuticular waxes of higher plants, were largely predominant in the whole area as indicated by n-C25-C40 carbon preference indices (CPI25-40) higher than 3 (Table 1). This may be the result of several factors: (1) the low productivity of the Mediterranean, particularly the open sea waters (23); (2) the preferential preservation of terrestrial over planktonic hydrocarbons in the marine environment, due to the more refractory matrix of continental sources (24); (3) the incidence of the atmospheric inputs, being the long-chain alkanes of the major components of the Mediterranean aerosol (25). These features reflect that the NW Mediterranean basic may act as a sink for terrestrially derived organic matter. On the other hand, a slight but consistent difference in the maximum carbon number of terrestrial alkanes was observed between the coastal and the deep sea sediments (Table 1). Samples close to the river mouths exhibited profiles maximizing either at n-C29 or n-C31 alkanes, whereas the distribution in deep sediments clearly

FIGURE 2. Chromatographic GC-FID profiles of aliphatic hydrocarbons in different marine sediments. A, BC8 (slope); B, BC5 (Gulf of Lions); C, A1 (off Barcelona). Numbers allocated on the peak apex denote the carbon number of the homologous serie of n-alkanes; P, pristane; F, phytane; LABs, linear alkylbenzenes; *, triterparne hydrocarbons; i.s., internal standard.

maximized at n-C31. This feature can be attributed to the preferential transport of fine particles, enriched in the higher carbon numbered n-alkanes (26) to the deep basin, whereas the coarse ones are preferently deposited in the shallow areas. A similar trend was already observed by other authors in the Rhone prodelta (27). In the proximity of urban (Marseille and Barcelona) and riverine (Rhone and Ebro) discharges, the ubiquitous continental component (n-C27, n-C29, and n-C31) is diluted by different proportions of fossil hydrocarbons, characterized by an homologous series of n-alkanes with CPI∼1. Moreover, a series of resolved components in the lower part of the chromatogram, corresponding to linear alkylbenzenes (LABs) (Figure 2C), indicates contributions from


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TABLE 1

Concentrations (Dry Wt) of n-Alkanes (n-ALK) and Unresolved Complex Mixture (UCM) in Sediments from the NW Mediterranean Seaa area prodeltab

Rhone Ebro prodeltac Barcelonad Gulf of Lionse Ebro shelf & slopef Catalan coastg Western deep basinh Eastern deep basini

TOC (%)

[n-ALK] (µg g-1)

[UCM] (µg g-1)

CPI25-40

n-C31/n-C29

P/F

C17/P

C18/F

1.0-2.1 0.7-1.2 1.8 0.8-1.2 0.4-0.7 0.8-1 0.8-1.1 0.7-1.5

10-27 (17.4) 1.1-1.8 (1.5) 7.7 0.8-2.3 (1.2) 0.3-1.1 (0.6) 1.1 (1.1) 1.1-1.7 (1.4) 1-1.2 (1.1)

76-275 (162) 8-17 (13) 488 7-17 (14) 0-15 (9) 17-23 (20) 7-13 (11) 8-11 (9)

2.6-4.3 (3.4) 4.4-7.6 (5.3) 1.5 1.6-5.5 (3.8) 3.5-5 (4.2) 2.4-4 (3.2) 3.1-4 (3.5) 3-4 (3.5)

na 0.78-1.15 (0.98) 1.17 1.02-1.27 (1.14) 1.05-1.31 (1.21) 0.89-1.36 (1.13) 1.16-1.32 (1.23) 1.24-1.37 (1.28)

na 2.2-5.1 (3.8) 1.4 2.7-5.5 (3.7) 1.9-2.9 (2.4) 1-1.4 (1.2) 1.8-2.7 (2.3) 1.7-3.1 (2.4)

1.1-2 (1.6) 1-1.3 (1.1) 0.8 1.3-2.3 (1.6) 1.2-1.9 (1.6) 0.8-5 (2.9) 1.2-2.1 (1.5) 1.2-1.8 (1.5)

na 1.4-2.2 (2) 0.6 3.1-5.6 (4.3) 2.6-3 (2.8) 0.9-5.3 (3.1) 2-4.8 (3.2) 1.8-3.8 (2.9)

a Additional parameters are given: carbon preference index of C -C 25 40 n-alkanes (CPI25-40), pristane/phytane (P/F), n-C17/pristane (C17/P), n-C18/ phytane (C18/F). Average values are given in parentheses. na, not available. b After Lipiatou and Saliot (13): RD5-RD11 stations. c BC7, BC11, C1, d e D1, and D2 stations. A1 station. TY8, TY14, TY23, BC4, BC5, and BC6 stations. f BC9, D3, and BC8 stations. g A2 and BC10 stations. h TY19, TY27, and BC12. i BC14, BC15, TY3, and TY17 stations.

domestic anionic surfactants (28). The concurrence in these samples of a UCM of hydrocarbons, which consists in a complex mixture of alicyclic hydrocarbons (29), is a positive indication of chronic/degraded petroleum contamination (30). A solid confirmation of this pollution was obtained from the m/z 191 mass fragmentograms, which exhibited a series of extended C32-C35 hopanes (22S and R) characteristic of oil-derived hydrocarbons (31). The contribution of petrogenic sources can also be evaluated using the relative concentrations of isoprenoids, particularly pristane (P) and phytane (F). In general, P/F values close to 1, such as in the Catalan Coast (Table 1), indicate a petrogenic source. However, this ratio can be affected by the occurrence of zooplankton-originated pristane. Thus, maximum values of P/F were found in the Ebro prodelta (2.2-5.1) and the Gulf of Lions (2.7-5.5), consistent with the above recognized higher abundance of planktonic indicators. On the other hand, the n-C17/ pristane and n-C18/phytane ratios, which elucidate the microbial degradation of n-alkanes (32), are always higher than 1 except in the stations from the Barcelona coast, where a clear evidence of biodegradation was observed. The concentrations of total n-alkanes is quite uniform in all sediments (about 1 µg g-1 dry wt) (Table 1) except in the vicinities of industrial areas such as Barcelona and Marseille (7 and 17 µg g-1 dry wt, respectively). It is interesting to notice that the n-alkane concentrations from the Rhone prodelta (10-27 µg g-1 dry wt) (13) are 1 order of magnitude higher than the ones from the Ebro (1.1-1.8 µg g-1 dry wt). Similarly, the spatial distribution of UCM exhibits the highest concentration near the above two cities with a negative gradient in seaward transects. Sediments from the Ebro prodelta exhibit moderate levels, comparable with those of the Gulf of Lions. Polycyclic Aromatic Hydrocarbons (PAHs). Twentytwo individual PAHs from phenanthrene to coronene and the corresponding alkylated species were determined in the collected sediment samples. Representative profiles of the major components, in urban and riverine areas and the deep sea basin, are illustrated in Figure 3. The general distribution reflects a high contribution of pyrolytic sources because of the predominance of parent PAHs (mainly structures with more than four rings) over their alkylated derivatives. This is particularly apparent in the deep sea samples. Nevertheless, a higher contribution of alkylated PAHs (mainly alkylphenanthrenes) is also evident in samples off Barcelona as well as in the Rhone and Ebro

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deltas. This pattern is attributed to petrogenic sources (33) and/or to exhaust emissions from the noncatalyst automobiles and heavy-duty diesel trucks (34). In the Ebro Delta, the main component is perylene, a naturally derived PAH (35), as will be discussed below. Table 2 shows the concentrations and relative contribution of PAHs depending on their sources: pyrolytic, fossil, and diagenetic. Pyrolytic PAHs include all parent compounds except phenanthrene, anthracene, and perylene. These last three compounds are not included in this group because of their unspecific origin: pyrolytic and/or fossil for the first two (36) and diagenetic and/or pyrolytic for perylene (35). Although pyrene and chrysene have also multiple origins, they are included in the pyrolytic class because of the predominant pyrolytic profile observed in the analyzed samples. On the other hand, alkylated PAHs and phenanthrene/anthracene are included in the fossil PAHs because the low-temperature pyrolytic processes, which also generate these compounds, are considered not relevant in the region. Finally, the natural/diagenetic PAHs are represented by perylene and retene. The highest concentrations of pyrolytic and fossil PAHs were found in sediments from the Rhone prodelta and offshore Barcelona, whereas 1 order of magnitude lower levels were encountered in the Ebro prodelta and other coastal sites far from urban/industrial inputs, which exhibit values comparable to the ones reported in nonpolluted areas of the Adriatic Sea (37) and the Spanish (38) and French (8) coasts. High concentrations of perylene (>100 ng g-1 dry wt) were found in the Llobregat and Ebro prodeltas, where its contribution represents up to 52% of the total PAHs. Although perylene is also produced by pyrolytic processes, whenever its content is higher than 10% of the whole mixture, it can be considered as originated from the diagenetic processes of continental organic matter in anoxic conditions (35). In the Rhone prodelta, however, perylene accounted for only 2-5% of the anthropogenic PAHs, but other naturally derived PAHs such as tetrahydrochrysenes were also detected (39). These compounds were present only at trace levels in the Ebro and Llobregat Deltas (38). Retene, another naturally derived PAH, was also found at high levels near the Rhone River mouth (13-68 ng g-1) (39) whereas in the Ebro Delta the levels were significantly lower (0.2-4.1 ng g-1). The differences observed between the French (Rhone) and the Spanish (Ebro and Llobregat) deltas regarding the occurrence of naturally derived PAHs could

FIGURE 3. PAH distribution in sediments from the northwestern Mediterranean Sea. F, phenanthrene; C1F, methylphenanthrenes; C2F, dimethylphenanthrenes; A, anthracene; Fl, fluoranthene; P, pyrene; C1Fl, methylfluoranthenes; BaA, benz[a]anthracene; Cr, chrysene/triphenylene; Bfl, benzofluoranthenes; BeP, benzo[e]pyrene; BaP, benzo[a]pyrene; IP, indeno[1,2,3-cd]pyrene; Bper, benzo[g,h,i]perylene; Per, perylene. TABLE 2

Concentrations of PAHs (Percent Contribution in Parentheses) and Sulfur (S-PACs) and Oxygen (O-PACs) Derivatives in Sediments from the NW Mediterranean Sea (in ng/g Dry Wt) PAHs

S-PACs

O-PACs

area

pyrolytica

fossilb

diageneticc

DBTsd

BNTse

NTFsf

BNFsg

Rhone prodeltah Ebro prodeltai Barcelonaj Gulf of Lionsk Ebro shelf & slopel Catalan Coastm Western deep basinn Eastern deep basino

1225-2427 (61) 62-191 (37-59) 3705 (77) 420-764 (76-87) 58-232 (73-83) 336-479 (84-88) 434-604 (76-86) 147-569 (80-90)

705-741 (34) 14-47 (10-14) 538 (11) 33-122 (8-12) 12-63 (11-20) 39-45 (8-10) 67-112 (10-17) 24-75 (6-15)

111-162 (5) 53-141 (19-52) 594 (12) 8-61 (1-6) 2-4 (0.6-5) 3-5 (0.5-1) 4-10 (0.6-2) 1-7 (0.6-1)

245-429 0.1-2 7.5 2.5-7 0.3-2.4 0.9-1.7 1.3-4.3 1-3.8

30-89 0.7-5 70 10-22 1-11 9-10 11-15 4-12

nap nd -0.7 4 nd-1 nd-0.6 nd-0.3 0.4-0.5 0.02-0.6

na 0.7-8 98 6-19 2-7 6-10 9-11 3-10

a Include fluoranthene, pyrene, benzo[a]fluorene, benzo[b]fluorene, benzo[c]phenanthrene, benz[a]anthracene, chrysene and triphenylene, benzo[j+b+k]fluoranthenes, benzo[a]fluoranthene, benzo[e]pyrene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, benzo[ghi]perylene, benzo[ghi]fluoranthene, dibenz[a,h]anthracene, benzo[b]chrysene, and coronene. b Include alkylated PAHs, phenanthrene, and anthracene. c Include perylene and retene. d Include dibenzothiophene and methyldibenzothiophenes. e Benzonaphthothiophenes. f Naphthothiophenes. g Benzonaphthofuranes. h After Lipiatou and Saliot (10, 11): RD5, RD6, RD7, RD8, RD10, and RD11 stations. i BC7, BC11, C1, D1, and D2 stations. j A1 station. k TY8, TY14, TY23, BC4, BC5, and BC6 stations. l BC9, D3, and BC8 stations. m A2 and BC10 stations. n TY19, TY27, and BC12. o BC14, BC15, TY3, and TY17 stations. p na, not available; nd, not detected.

be related either to the concurrence of precursors coming from vegetation of the drainage basins or to the different depositional conditions. In all cases, a steep decrease of concentrations in seaward transects allowed the recognition that a significant portion of the deposition of these continental inputs takes place in the Continental Shelf at water depths shallower than 70 m. Particularly noticeable are the relatively high concentrations of pyrolytic PAHs observed in the deep basins, suggesting as a potential source the atmospheric deposition from PAH-enriched air masses coming from northern Europe. The individual composition of PAH components in aerosol and sediment samples and the atmospheric and

sedimentary flux calculations support this assumption. In fact, PAHs originated in combustion processes are associated to small (submicron) particles that can be long-range transported far from their sources (3). After deposition on the water surface, these particles can be efficiencly transported to the deep sediment through vertical transport by zooplankton fecal pellets (4). The Mediterranean aerosol (40) and the deep sea sediments exhibit similar PAH distributions, which are generally depleted in the most photoreactive components (e.g., benzo[a]anthracene and benzo[a]pyrene), reflecting the “weathering” of an aerosol after long-range transport (41). The BaA/(BaA + Cr) ratio, for instance, varies from 0.52-0.37 in the coastal zone (e.g.,


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FIGURE 4. Mass fragmentograms of the corresponding molecular ions of polycyclic aromatic ketones by GC-MS-NICI. 1, 9H-fluoren9-one; 2, anthrone or phenanthrone; 3, 4H-cyclopenta[def]phenanthren-4-one; 4, benzo[a]fluoren-9-one; 5, benzo[c]fluoren-9-one; 6, benzo[b]fluorene-7-one; 7, 7H-benz[de]anthrancen-7-one; 8, benzopyrenones; 9, indenopyrenones; 10, dibenzofluorenones.

Barcelona, Rhone, and Ebro prodeltas) to 0.30-0.27 in the deep sea samples. The last section of this paper will address the coupling of the corresponding atmospheric and sedimentary depositional fluxes. Although the contributions of diagenetic and fossil PAHs are relatively important in areas influenced by river discharges and urban activities, the ubiquitous representation of pyrolytic inputs in NW Mediterranean sediments may also be associated to the fact that the combustiongenerated PAHs appear to be more strongly associated with particles than the petroleum-derived ones, thus becoming less available for degradation (42). Sulfur/Oxygenated Heterocyclic Compounds. Sulfur and oxygen PAH derivatives were identified in all samples. Among them, dibenzothiophenes (DBTs) and benzonaphthothiophenes (BNTs) were the predominant compounds (Table 2). Although the DBT series cannot be univocally assigned to petrogenic or pyrolytic sources (43), the high concentrations found in the Rhone prodelta, concurrently with those of alkylphenanthrenes, suggest a common petrogenic origin. In turn, benzonaphthothiophenes, mainly represented by the benzo[b]naphtho[2,1-cd]thiophene, were even more abundant in all samples and more evenly distributed in the whole basin. These are indicators of coal and diesel combustion sources (44-47). However, as other abundant compounds in coal samples like naphthothiophenes (NTFs) were present at much lower levels (Table 2), we may assume a major petrogenic combustion source for BNTs. Regarding the oxygenated polycyclic aromatic compounds (PACs), benzonaphthofurans (BNFs) were found in all sediment samples. These are found in a variety of sources, such as lignite combustion (48), lubricating oils (48, 49), and coal tar (50). However, their presence in deep sediments at concentrations even higher than those of coastal sites (Ebro Delta) suggests, as the majority of parent PAHs, a pyrolytic source. Polycyclic aromatic ketones and quinones were detected in all sediments by negative chemical ionization mass spectrometry in concentrations ranging from 1 to 24 ng g-1

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in the case of fluorenone derivatives (22). Figure 4 illustrates current profiles of these ketones. They are mostly originated by the combustion of fossil fuels or wood (45, 51) and, therefore, have been identified in urban particulate matter (52). Moreover, they can be formed by photooxidation during atmospheric transport of soot particles (45, 53). Urban runoff has been recognized as the prevalent source of these compounds in coastal sediments (54), although a direct atmospheric deposition of aerosol particles cannot be overlooked. Particularly, the alkylated homologs of fluorenone are typical of diesel and noncatalyst automobile exhausts (34, 55, 56). However, the different distributions reported between urban particulate matter and coastal sediments might indicate that some oxidation and selective degradation processes may take place during sedimentation (22). Historical Trends. Two dated sediment cores from the Rhone and Ebro Continental Shelves (BC4 and BC9 in Figure 1) were selected for assessing the historical trends of the deposition of aliphatic and aromatic hydrocarbons in the region. The depth profiles of the different components are indicated in Table 3. The n-alkane concentrations exhibit a similar trend in both cores, representing an increase by a factor of 2 during the last 100 years. In the case of the Ebro, this increase has been accompanied by a reduction of the CPI25-40, indicating a certain contribution of petrogenic hydrocarbons. In fact, the UCM of aliphatic hydrocarbons shows a steep increase by a factor of 10 in that period. In the Rhone area, however, this increase started earlier, in the 1920s, and achieved almost a stabilization in the 1960s until the present time. PAHs reflect the chronological record on the sediment core more accurately than aliphatic hydrocarbons because they are less prone to degradation or remineralization (57). Their distribution patterns in the different core horizons are dominated by pyrolytic sources, although the fossil contribution increases relatively in the lower sections. The PAH concentrations raise exponentially in both cores in the early 1900s, at the beginning of the industrial development. During the period of 1920-1940, a submaximum of concentration is observed that could be related to the increasing combustion of coal. A slight decrease in the period 1940-1960 is attributed to the substitution of coal for oil and liquified gases at most of the home heaters. In fact, it is well-known that coal home combustion is an inefficient combustion process leading to higher PAHs levels than industrial coal or petroleum derivatives (58). A subsequent maximum appears later, in the 1970s, in accordance with data from sediment cores collected in other European sites (10, 59-62). The PAH concentrations in the Ebro area remain fairly constant since 1960 whereas in the Rhone area they increase considerably during the period 1975-1990. Analysis of the surficial sediments shows, however, a significant decrease of the PAH during the last 5 years (1985-1990) in both areas. This decline could be partially attributed to improvements in emission controls and to the continuous substitution of oil fuels by liquefied gases for space heating and electricity generation. Fluxes of anthropogenic hydrocarbons (UCM, PAHs, and sulfur/oxygen PACs) were calculated for both areas (Table 4) using the concentration data from Table 3, and sedimentation rates and sediment densities were provided by Zuo (17, 18). The UCM fluxes were similar at the end of last century in both areas, increasing more significantly in the Rhone during the 1920-1960 period but being exceeded

TABLE 3

Concentrations of Hydrocarbons and Sulfur/Oxygen Heterocycles (in ng/g Dry Wt) in Sedimentary Column from the BC4 and BC9 Samples Located, Respectively, in the Rhone and Ebro Continental Shelfa

a

BC4 (Rhone)

1840-1980 (30-22 cm)

1920-1940 (14-10 cm)

1940-1960 (10-6 cm)

1960-1975 (6-3 cm)

1975-1990 (3-0 cm)

1985-1990 (1-0 cm)

n-alkanes CPI25-40 UCM pyrolytic PAHs fossil PAHs diagenetic PAHs S-PACs O-PACs

830 4.3 1798 132 (72) 37 (20) 5 (3) 6 (3) 5 (3)

959 3.3 8992 1146 (87) 112 (8) 19 (1) 28 (2) 19 (1)

962 4.2 9683 1089 (86) 113 (9) 21 (2) 27 (2) 20 (2)

1066 4.1 12040 1214 (84) 147 (10) 26 (2) 36 (3) 23 (2)

1699 4.4 11110 1712 (82) 240 (11) 48 (2) 60 (3) 39 (2)

967 5.4 13340 420 (87) 34 (7) 12 (3) 12 (3) 6 (1)

BC9 (Ebro)

1880-1920 (22-14 cm)

1920-1940 (14-10 cm)

1940-1960 (10-6 cm)

1960-1975 (6-3 cm)

1975-1990 (3-0 cm)

1985-1990 (1-0 cm)

n-alkanes CPI25-40 UCM pyrolytic PAHs fossil PAHs diagenetic PAHs S-PACs O-PACs

458 4.9 1072 27 (77) 5 (14) 2 (5) 1 (2) 1 (2)

548 4.4 3676 216 (84) 21 (9) 7 (3) 5 (2) 4 (2)

534 3.4 5632 197 (85) 18 (9) 4 (2) 5 (3) 4 (2)

564 3.7 6655 301 (87) 25 (8) 6 (2) 6 (2) 4 (1)

854 2.8 11795 293 (83) 32 (11) 7 (2) 8 (3) 5 (2)

498 4.1 12056 221 (83) 25 (11) 2 (1) 7 (3) 5 (2)

Percentage contributions to the total PAHs are given in parentheses.

TABLE 4

Fluxes of Hydrocarbons (ng cm-2 yr-1) through Sedimentary Record BC4 (Rhone) UCM PAHs pyrolytic fossil diagenetic S-PACs O-PACs BC9 (Ebro) UCM PAHs pyrolytic fossil diagenetic S-PACs O-PACs

1840-1980 (30-22 cm)

1920-1940 (14-10 cm)

1940-1960 (10-6 cm)

1960-1975 (6-3 cm)

1975-1990 (3-0 cm)

1985-1990 (1-0 cm)

387

1630

1714

1986

1732

2055

28 8 1 1 1

208 20 3 5 3

193 20 4 5 3

200 24 4 6 4

267 37 7 9 6

65 5 2 2 1

1880-1920 (22-14 cm)

1920-1940 (14-10 cm)

1940-1960 (10-6 cm)

1960-1975 (6-3 cm)

1975-1990 (3-0 cm)

1985-1990 (1-0 cm)

289

941

1374

1624

2760

2952

7 1 0 0 0

48 5 2 1 1

43 4 1 1 1

66 6 1 1 1

59 8 2 2 1

46 6 1 2 1

by the Ebro in the last decade due to the stabilization of the inputs in the former area. Concurrently, the fluxes of PAHs and sulfur/oxygen PACs in the Rhone sedimentary column were 4-6 times higher than in the Ebro, although they were similar in the surface sediment, thus reflecting the high reduction of hydrocarbon inputs in the Rhone area over the last 5 years. Estimates of Sedimentary Fluxes and Budgets. Depositional fluxes of aliphatic and aromatic hydrocarbons estimated from their concentrations in surficial sediments, sediment densities, and sedimentation rates calculated by 210Pb dating (17, 18) are reported in Table 5. The Rhone prodelta exhibits accumulation rates ca. 25 times higher than those in the Ebro prodelta, whereas those corresponding to the Barcelona coast exhibit intermediate values. The Gulf of Lions and the Ebro Continental Shelf and slope show comparable values but at levels much lower than the ones mentioned above. On the other hand, the fluxes in the western deep sea basin were higher than in the eastern part, probably due to the vicinity of the continent and to

the effect of the Liguro-Provenç al current, which is carrying more contaminants from the Gulf of Lions and the Rhone prodelta westwards. Interestingly, the mean PAH fluxes for the whole deep sea basin are comparable to those estimated for the atmospheric deposition (dry and wet) in the NW Mediterranean (3-16 ng cm-2 yr-1) (3, 63), which are of the same order of the atmospheric dry deposition found in remote areas from United States (0.3-17 ng cm-2 y-1) (64, 65). Moreover, they are very close to those estimated from particle interceptor traps in the deep water column (66), clearly suggesting that atmospheric transport is the main source of PAHs to the deep Mediterranean basin and confirming the refractory behavior of pyrolytic PAHs during sedimentation. Conversely, atmospheric n-alkane fluxes (71-442 ng cm-2 y-1) (3, 63) are slightly higher than those estimated from the sediments, probably reflecting the relevance of degradation processes affecting these hydrocarbons before being incorporated into the deep sediments.


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TABLE 5

Deposition Fluxes of Hydrocarbons in Surface Sediments from the NW Mediterranean Seaa area

n-alkanes (ng cm-2 yr-1)

UCM (µg cm-2 yr-1)

PAHs (ng cm-2 yr-1)

Rhone prodeltab Ebro prodeltac Barcelona offshored Gulf of Lionse Ebro shelf & slopef Catalan coastg Western deep basinh Eastern deep basini

5000-18000 (11000) 270-697 (471) 1231 71-153 (113) 93-117 (101) 113 46-63 (53) 10-27 (18)

38-220 (110) 1.8-7.3 (4.3) 78 0.6-2.0 (1.4) 0-2.9 (1.4) 2.2 0.26-0.7 (0.5) 0.08-0.2 (0.14)

491-1798 (1067) 12-75 (39) 501 29-68 (50) 16-39 (24) 30 16-19 (17) 1-10 (5)

a Average values are given in parentheses. b After Lipiatou and Saliot (13): RD5, RD6, RD7, RD8, RD10, and RD11 stations. c BC7, BC11, C1, D1, and D2 stations. d A1 station. e TY8, TY14, TY23, BC4, BC5, and BC6 stations. f BC9, D3, and BC8 stations. g A2 station. h TY19, BC10, TY27, and BC12 stations. i BC14, BC15, TY3, and TY17 stations.

TABLE 6

Annual Accumulation Rates of Hydrocarbons in Surficial Sediments from the NW Mediterranean Sea area

surface (km2)

UCM (t/yr)

PAHs (t/yr)

Rhone prodeltaa Ebro prodeltab Barcelona offshorec Lion Gulfd Proven¢encal coaste Ebro shelf & slopef Ligurian seag Catalan coast & Valencia gulfh Western deep basini Eastern deep basinf NW Mediterranean

640 700 112 21360 21640 12600 53000 8500 64000 98000 280552

704 30 87 299 303 176 477 153 320 137 2686

6.8 0.3 1.2 10.7 10.8 3 7.7 2.2 11 5 60

a From Lipiatou and Saliot (13): RD5, RD6, RD7, RD8, RD10, and RD11 stations. b BC7, BC11, C1, D1, and D2 stations. c A1 station. d TY8, TY14, TY23, BC4, BC5, and BC6 stations. e Assuming the same fluxes as Lion Gulf. f BC9, D3, and BC8 stations. g UCM flux from Monaco sediment (10) and PAHs fluxes from sediment straps of Monaco (67). h Fluxes from the shelf & slope Ebro and A2 station. i Concentrations reported from the Valencia Gulf sediments (38) are close the ones found in the Ebro Continental Shelf and slope and Catalan coast: TY19, BC10, TY27, and BC12. j BC14, BC15, TY3, and TY17 stations.

The inputs of anthropogenic hydrocarbons (UCM and PAHs) over the last 5-10 years to the NW Mediterranean surficial sediments were estimated from the fluxes calculated above and from the mean surface areas defined in Table 6. Considering that the mass of contaminants accumulated on the estaurine sediments is the result of the contaminant river loadings, we may conclude that the amount of hydrocarbons transported by the Rhone River is 1 order of magnitude higher than that carried by the Ebro. The UCM accumulation in the Rhone prodelta closely agrees with previous estimates of petroleum hydrocarbons transported by the Rhone River (800 T yr-1) (68). Furthermore, PAHs carried out by the Rhone and Ebro Rivers (5.3-12 and 1.3 T yr-1, respectively) are similar (69, 70) to those accumulated in the sediments, indicating a higher mobility of these compounds in both prodeltas. Other estimates focused on some restricted areas of the basin are in fairly good agreement with the ones given in Table 6. Petroleum (UCM) and pyrolytic (PAHs) hydrocarbon inputs in the Gulf of Lions were estimated by Lipiatou and Saliot (13) in 410 and 6.2 T yr-1, respectively, through the sediment load deposited in an area of 15340 km2. Based on sediment fluxes, an input of 7.8 T yr-1 of

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9


PAHs was also calculated for an area of 790 km2 in the Rhone prodelta (3). Considering these values, our data suggest that the hydrocarbons inventories previously reported for the west Mediterranean (71) are overestimated. In any case, the values given in Table 6 for aliphatic and aromatic hydrocarbons are the first based on field data covering the whole basin and show the importance of scavenging processes of riverine pollutants in the coastal zone and the predominance of atmospheric deposition in the deep sea basin.

Acknowledgments Financial support was obtained from the Environment Program of the EU under the Project EROS-2000 (Contract EV4V0111F) and by the Research Funding Spanich Agency (CICYT, Grant NAT 93-0693). I.T. acknowledged a Ph.D. fellowship from the Catalan Education Ministry (Generalitat de Catalunya). Personnel on-board R/V Marion Dufresne, R/V Garcia del Cid, and R/V Tyro are kindly acknowledged for their helpful assistance.

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Received for review October 23, 1995. Revised manuscript received March 18, 1996. Accepted April 4, 1996.X ES950647X X

Abstract published in Advance ACS Abstracts, June 1, 1996.


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Oxygen

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