Environ. Sci. Technol. 2000, 34, 5067-5075
The Aegean Sea Oil Spill. 2. Temporal Study of the Hydrocarbons Accumulation in Bivalves CINTA PORTE, XAVIER BIOSCA, DOLORS PASTOR, M O N T S E R R A T S O L EÄ , A N D J O A N A L B A I G EÄ S * Department of Environmental Chemistry, CID (CSIC), Jordi Girona, 18-26, 08034 Barcelona, Spain
Aliphatic and aromatic hydrocarbons were determined in tissues of mussels (Mytilus edulis), clams (Tapes semidecussata), cockles (Cardium edule), and oysters (Ostrea edulis), collected 3, 6, 9, 12, and 34 months after the Aegean Sea oil spill occurred in the Galicia coast (NW Spain) in December 1992. Petroleum uptake was confirmed by the presence of an unresolved complex mixture of hydrocarbons containing fossil markers, such as triterpanes and saturated and aromatic steranes. These markers were useful in assessing the spatial and temporal evolution of the spilled oil in the area, resulting in the pregnane derivatives particularly enriched in the bivalve tissues. The distribution of parent 3-6-ring polycyclic aromatic hydrocarbons reflected the concurrence of oil residues and combustion products, possibly from the tanker fire. These distributions were depleted in higher ring components with respect to those found in sediments, indicating a lower bioavailability of the pyrogenic components but a longer persistence in time. Qualitative and quantitative differences in bioaccumulation were found among bivalves, sampling sites and over time. Aliphatic and aromatic hydrocarbons also exhibited different bioaccumulation trends. A significant decline of the hydrocarbon contents was particularly evident from 3 to 6 months after the accident, although incidental increases, probably related to the resuspension of the polluted sediments by stormy weather, were observed.
Introduction On December 3, 1992, the Aegean Sea tanker, transporting 79 000 tons of a light crude oil (Brent type, North Sea), ran aground off La Corun ˜ a on the Galicia coast (NW Spain). The tanker immediately leaked oil, and a series of explosions set it on fire, that could not be completely extinguished before 6 days. The winds and sea currents drove the petrogenic and pyrolytic hydrocarbons toward the north and east (see Figure 1) affecting an area of 60 km2 and 200 km of coastline. This coastline is highly broken, forming a large suite of estuaries (“rias”) which provide advantageous conditions for shellfish growing and culturing. Therefore, soon after the incident a monitoring program was established by the Spanish authorities in order to assess * Corresponding author phone: +34-93-4006152; fax: +34-932045904; e-mail:
[email protected]. 10.1021/es000064+ CCC: $19.00 Published on Web 11/10/2000
2000 American Chemical Society
the spatial and temporal evolution of petrogenic and combustion compounds in bivalves from several locations along the coast and inside the estuarine areas, where bivalves are commercially produced and oil was less exposed to weathering. Sampling of mussels (Mytilus edulis), clams (Tapes semidecussata), cockles (Cardium edule), and oysters (Ostrea edulis) took place 3, 6, 9, 12, and 34 months after the accident, in the stations indicated in Figure 1. Among the enormous variety of hydrocarbons present in the marine environment (1), acyclic isoprenoids, steranes, and terpanes have been suggested as passive tags for source recognition of oil spills by mass fragmentography (2). Steranes and triterpanes have been found particularly suitable for source identification of petroleum residues in coastal sediments (3-5) and stranded tar balls (6, 7). However, less interest has risen on their use in bivalves affected by oil spills (8, 9). Although these compounds are not known to be toxic to marine organisms, they are useful in marine pollution monitoring from different standpoints. They are as follows: (a) hydrophobic, so likely bioaccumulated and giving a measure of the organisms exposure; (b) related to the origin of the oil, so of diagnostic value for the identification of the hydrocarbons source; (c) quite resistant to degradation, so of particular interest in the assessment of temporal trends; and (d) easily determined by GC-MS. Therefore, these chemical markers will be extensively used in the present study. On the other hand, polycyclic aromatic hydrocarbons (PAHs) are ubiquitous components in the marine environment, and the ratios between parental and alkylated are used for differentiating hydrocarbon sources (10). PAHs originated at high temperatures (combustion) are dominated by the parent species, in contrast with crude oils, that contain a wide range of alkyl-derivatives. As part of the oil spilled by the Aegean Sea was burned, the relative distribution of alkylated and dealkylated species will also be a parameter of interest in the appraisal of the extension of the spillage impact on the biotic compartment. A previous study concerning the distribution and fate of hydrocarbons from the Agean Sea oil in coastal sediments (11) has shown the usefulness of the chemical marker approach. Taking into account the information available, the present study is aimed for a deeper insight into the impact of the oil on bivalves and the assessment of the natural cleaning processes of the coastal environment, involving both petrogenic and pyrolytic hydrocarbons.
Experimental Section Sample Collection and Preparation. Mytilus edulis (4.35.7 cm length; 1.9-2.2% lipids fresh weight), Tapes semidecussata (3.7-4.6 cm length; 1.4-1.5% lipids), Cardium edule (2.8-3.4 cm length; 1.0-1.1% lipids), and Ostrea edulis (5.87.5 cm length; 1.6-1.8% lipids) were collected from indigenous populations along the Galicia coast. Sampling was performed 3, 6, 9, 12, and 34 months after the accident, in the stations indicated in Figure 1. These included reference stations, north and south of the tanker wreck site (1. Malpica; 2. Leira; 14. Meira´s), stations differently affected by the spill, in the estuaries of La Corun ˜ a (3. Pasajes; 4. Mera), Betanzos (5. Lorbe´; 7. Perbes), Ares (8. Pontedeume; 9. Redes), and El Ferrol (10. La Palma; 11. Barallobre; 12. Xubia; 13. Carin ˜ o), and a farming site (6), in open waters, in the “rias” of Ares and Betanzos. VOL. 34, NO. 24, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Map of the area of study showing the grounding site of the Aegean Sea (*), the movements of the oil spill and the pyrolytic material, and the bivalve sampling stations. Whole bivalve tissues were separated from the shells, wrapped in clean aluminum foil, and stored at -20 °C until chemical analysis. Individuals from each station (10-20) were pooled, homogenized, and freeze-dried. Chemical Analysis. Approximately 2 g of freeze-dried tissues was spiked with squalane and deuterated pyrene as surrogates, saponified with 100 mL of methanolic 6 N KOH at 40 °C overnight, and extracted with 3 × 100 mL hexane: dichloromethane (4:1) to obtain the total organic extracts. These were further resolved by column chromatography (5% water-deactivated silica-alumina) in two fractions, eluted with n-hexane (alkanes + alkenes) and n-hexane:dichloromethane (9:1 and 8:2) (mono- and polycyclic aromatics, respectively) (12). The first fractions were analyzed by capillary GC-FID using a Carlo Erba model Mega 5300, equipped with a 30 m × 0.25 mm ID CP-Sil 5 CB fused silica column (Chrompack, Middleburg, The Netherlands), temperature programmed from 60 to 100 °C at 15 °C/min and from 100 to 300 °C at 6 °C/min, with a final hold-up during 10 min. The injector and detector temperatures were 270 and 310 °C, respectively. The carrier gas was hydrogen. Resolved components (RH) were quantified by comparison with an external standard mixture containing C14, C15, C16, C22, C23, C24, C28, C32, and C36 n-alkanes. The unresolved complex mixture (UCM) of hydrocarbons was quantified using the response factor of the n-alkane eluting in the zone of maximum response (usually C20-C26). These fractions were also analyzed by computerized gas chromatography-mass spectrometry (GC-MS) for the determination of the fossil marker profiles (hopanes m/z 191, and steranes m/z 217/218). The instrument was a Fisons 800 GC interfaced to a Fisons MD 800 MS, operating with the same chromatographic conditions reported previously, except the carrier gas that was helium. The aromatic fractions were combined and also analyzed by GC-MS in the selected ion monitoring (SIM) mode with the acquisition of the parent ions for phenanthrene + anthracene (178), dibenzothiophene (184), fluoranthene + pyrene (202), benz[a]anthracene + chrysene (228), benzo[b]+[k]fluoranthenes (252), benzo[a]pyrene (252), indeno[1,2,3-cd]pyrene + benzo[ghi]perylene (276), and dibenz[ah]anthracene (278). Full ion scan acquisition was also 5068
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performed for confirmation and for the determination of the alkylated series of the m/z 178, 184, and 228 parent compounds as well as the aromatized sterane derivatives (m/z 231, 245, and 253) (11). The percentage of lipids (fat) were determined by Soxhlet extraction of the freeze-dried samples with hexane:dichloromethane (4:1). Analytical Performance. The above-reported methods included the processing of blanks, duplicates, and standard mixtures between batches of four samples. Squalane and deuterated pyrene were used as surrogates for calculating the recoveries that were >80%. The GC injections were performed with an automatic injector to improve reproducibility that was
