Polycyclic aromatic hydrocarbons in recent sediments and mussels (Mytilus edulis) from the Western Baltic Sea: occurrence, bioavailability and seasonal variations
Introduction
The widespread occurrence of polycyclic aromatic hydrocarbons (PAHs) in recent sediments has been well documented (Youngblood and Blumer, 1975, Neff, 1979). These compounds have mainly anthropogenic origins (Wakeham et al., 1980), including the combustion of fossil or recent organic matter and the release of hydrocarbon related to petroleum explorations. Natural PAHs can be produced by forest fires, related to natural seeps of petroleum, or derived from biogenic precursors (diagenesis). Each source is characterised by a specific molecular pattern and it is, therefore, possible to determine which source generated these compounds.
The bioavailability of sediment-associated hydrocarbons depends on compound physico-chemical properties, sediment characteristics and characteristics of the different organisms (Knezovich et al., 1987, Landrum and Robbins, 1990). The main parameter governing sediment-associated compound bioaccumulation is the hydrophobic character of the compound. The lowest molecular weight and most water-soluble compounds are the most bioavailable (Hellou et al., 1993, Djomo et al., 1996). Sediment organic carbon content (Knezovich et al., 1987), grain-size distribution (Harkey et al., 1994), interstitial water (Harkey et al., 1995), sediment ageing (Landrum et al., 1992, Kesley et al., 1997), and PAH origin (Murray et al., 1991) are parameters influencing contaminant bioavailability. Exposure of organisms to pollution depends on water turbidity (Foster et al., 1987, Pruell et al., 1987), location of the organism in the water column (Roesijadi et al., 1978) and on feeding modes (Bjorseth et al., 1979, Swartz et al., 1990, Porte and Albaigés, 1993, Hickey et al., 1995). Several models have been developed to predict organism residue content induced by contaminants adsorbed on sediments (Di Toro et al., 1991), but because of the complexity of the phenomena governing xenobiotic uptake and depuration, it is difficult to predict organism residue content of xenobiotics (Baron, 1990).
The present work is focused on samples (sediments and mussels) from the Western Baltic Sea. Up to now, few papers report PAH occurrence in the Baltic Sea (Ehrhardt and Heinemann, 1975, Law and Andrulewicz, 1983, Broman et al., 1990, Witt, 1995). The interest of the present work is thus to provide information on the occurrence and fate of PAHs in German and Polish areas.
The sampling stations were chosen as related to pollution gradients. Some sediments close to very industrialised sites (Kiel harbour, Warnemünde harbour) are exposed to an important anthropogenic input while the sediments collected far from the coast are subjected to a lower pollution level. Fourteen parent PAH compounds among the 16 PAHs recommended as priority pollutants by the Environmental Protection Agency (EPA) were analysed. Seventeen additional aromatic compounds (alkylated and parent compounds) were studied because of the additional information they provide on PAH origin and fate.
Sediments were sampled to quantify PAHs and to estimate pollution levels in the different sites as well as the origins of the contamination. In the Baltic Sea the mussels are located on the bottom of the sea and are, therefore, the chosen bivalve to study sediment pollution impact on organisms. Mussels were collected and the PAH concentration of their tissues gave information on the contamination burden of organisms living in contact with the sediments. The comparison between mussel and sediment PAH concentrations gave information on the bioavailability of these pollutants, on the mussel exposure pathways and on the metabolic capacities of these bivalves. Finally, the sampling of sediments and mussels at different periods, but at the same stations, allows for the study of possible seasonal variations in sediment contamination level, mussel contaminant uptake and mussel metabolic efficiency.
Section snippets
Sampling
The samples were collected during three cruises which took place in the same area (27–31 March 1995, 23–27 October 1995 and 22–28 August 1996). The sites can be divided into four groups (Kiel, Warnemünde, Peenemünde, Oder areas) (Fig. 1, Table 1). Five samples from the Kiel harbour to the open sea constitute the Kiel gradient. Four stations from the Warnemünde harbour to the open sea form the Warnemünde transect. The third transect is constituted by four sites from Peenemünde towards the open
Contaminant levels
The surface sediments present a wide range of total parent PAH concentrations, from 3 to 30 000 ng/g of dry matrix if the three cruises are considered (Table 2). Comparable pollution levels were measured in the surface sediments of the Baltic Sea (Law and Andrulewicz, 1983, Witt, 1995). The two sets of sediments of Kiel and the Oder are polluted at high levels (30–30 000 ng/g) while the Peenemünde and the Warnemünde sediment pollution levels are quite low (3–1600 ng/g). The same contamination
Conclusions
Sediments and mussels have been sampled in various areas of the Baltic Sea to study sediment PAH occurrence along transects and their relation with filter-feeding organisms.
Over the three cruises that took place on three different transects from the coast to the open sea, we have observed contamination gradients in the sediments and the mussels. The sample contamination levels are high close to the pollution sources and decrease with increasing distance from the sources. The Oder river
Acknowledgements
EU (BIOMAR project, contracts EV5VCT94-550 and ENVCT96-31) are acknowledged for financial support, P.D. Hansen, U. Fiedler and Kiel Institute for the shipping facilities as well as the crew members, J.F. Narbonne for interesting discussions about the results, and S. Thompson for her careful reading of the manuscript.
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