Chernobyl radioactivity persists in fish

After the accident at the Chernobyl nuclear reactor in 1986, the concentration of radioactive caesium ( 134 Cs and 137 Cs) in fish was expected to decline rapidly. The estimated ecological half-life (the time needed to reduce the average caesium concentration by 50%) was 0.3 to 4.6 years 1 , 2 . Since 1986, we have measured radiocaesium in brown trout ( Salmo trutta ) and Arctic charr ( Salvelinus alpinus ), both of which are widely eaten in Scandinavia, in a lake contaminated by Chernobyl fallout 3 , 4 . We have measured radiocaesium in nearly 4,000 fish, taking samples 2-4 times every year from spring to autumn. We find that the decline in radiocaesium was initially rapid for 3-4 years and was then much slower. About 10% of the initial peak radioactivity declines with an ecological half-life of as long as 8-22 years.