Short- and long-term patterns of 137Cs in fish and other aquatic organisms of small forest lakes in southern Finland since the Chernobyl accident

We summarize the patterns of Cs-137 activity concentrations and transfer into fish and other biota in four small forest lakes in southern Finland during a twenty-year period following the Chernobyl accident in April 1986. The results from summer 1986 showed fastest accumulation of Cs-137 into planktivorous fishes, i.e. along the shortest food chains. Since 1987, the highest annual mean values of Cs-137 have been recorded in fish occupying the highest trophic levels, for perch (Perca fluviatilis) 13,600 Bq/kg (ww) and for pike (Esox lucius) 20,700 Bq/kg (ww). At the same time, activity concentrations of Cs-137 in crustacean zooplankton and Asellus aquaticus have ranged between 1000 and 19,500 Bq/kg (dw). In 2006, 5-28% of the 1987 Cs-137 activity concentration levels were still present in perch and pike. Since 1989 their Cs-137 activity concentrations in oligohumic seepage lakes have remained significantly higher than in polyhumic drainage lakes due to the increased transfer of Cs-137 into fish in the seepage lakes with lower electrolyte concentrations, longer water retention times and lower sedimentation rate. (C) 2011 Elsevier Ltd. All rights reserved.