EN
AChE activities were measured in blue mussels gills and flounder muscles samples collected off Poland – the Gulf of Gdańsk (4 sampling stations) and off Lithuania – the Klajp˙eda area (3 sampling stations), in 2001 (June and October) and 2002 (April and October). The AChE activities [nmol min−1 mg protein−1] were in the range: 15–38 (in blue mussels) and 94–315 (in flounder), and agreed well with those reported for flounder in other coastal Baltic areas, and other European seas. Sources of contaminants in the study area are rather localized in the Gulf of Gdańsk, (mouth of the Vistula due to runoff, ports, sewage discharges), while an accidental oil spill occurred off Lithuania, in the course of the study (November 2001). Geographical and temporal AChE levels changes followed the contamination pattern. AChE activities and gradients in the study area are well documented and confirmed in this study. The study confirms the potential use of AChE as biomarker of organic pollution.