¹³⁷Cs in fishes and water in Finnish lakes - considerations for radiological risk assessment

STUK - Radiation and Nuclear Safety Authority, PO Box 14, 00881 Helsinki, Finland

Abstract

The deposition from Chernobyl in spring 1986 was most unevenly distributed in Finland and elevated the ¹³⁷Cs contents of fishes in Finnish lakes significantly. High activity concentrations of ¹³⁷Cs still occur in fish from certain lakes in the areas of the highest deposition. Activity concentrations of ¹³⁷Cs in perch varied from 20 to 7 800 and those in lake water from 4 to 330 Bq/m³ in 1998 and 2002. Concentration factors (Bq/kg in perch / Bq/kg in lake water) ranged from 1 300 to 30 000 in the lakes studied. Ecological halftimes of ¹³⁷Cs in perch in certain lakes, monitored regularly since 1986, and representing different types in terms of environmental transfer, were estimated as examples. The longest halftimes of ¹³⁷Cs in perch were approximately 8 years and the shortest approximately 3 years determined for the time period of 1988-2002. Except for estimation of radiation doses to people eating fish, data on changes of activity concentrations in various parts of the aquatic system are also needed when estimating radiation doses to fish and other biota. Slow recovery of the habitat and feed from ¹³⁷Cs results in higher exposure of biota than in case of rapid activity decrease.