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.
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