Occurrence and transport of polycyclic aromatic hydrocarbons in the water bodies of the Baltic Sea

Between 1992 and 1998, 313 seawater samples were collected in the surface microlayer, the surface water and the deep water of the Baltic Sea. Fifteen individual parent polycyclic aromatic hydrocarbons (PAHs) were analyzed at 41 different coastal and offshore stations. The study has provided the most comprehensive information available to date about PAHs in different water bodies of the Baltic Sea. In general, the levels of the PAHs in Baltic Sea water were below 20,000 pg/l for the sum of 15 PAHs. Higher concentrations were found in estuarine samples. One local source in the southern Baltic Sea is the River Oder. Hot spots were observed mainly in the western Baltic Sea. In particular, high concentrations of the two- and three-ring PAHs were detected. Phenanthrene, fluoranthene and pyrene were the major components in surface water of the Baltic Sea. PAH composition profiles were compared to establish whether different water bodies of the Baltic have characteristic PAH patterns originating from characteristic inputs. Cluster analysis was used as pattern recognition technique. Four characteristic water bodies can be identified in the surface water in February (Mecklenburg Bight (MB), Pomeranian Bight (PB), the eastern (EZOS) and western central Baltic Sea (WZOS)). After the spring algae bloom, these patterns disappeared. This may be due to the cleaning of the water column after the bloom by large quantities of settling particulate matter that takes the PAHs with it to the sediment. A seasonal variation of the PAH concentrations was observed with the largest amounts in February followed by November, reflecting the increase of PAH sources during winter.