24 
200 TBq in 2006, corresponding to half of the 
90 Sr inventory in 1985, the year before the 
Chernobyl accident. Concentrations of 90 Sr 
decrease slowly with time, and its behaviour 
in seawater is different from 137 Cs. 90 Sr is 
more soluble in water, and its effective half- 
life in seawater is longer than that of 137 Cs, at 
around 20 years during 1987-2006. 
239,240p u 
Concentrations of 239 24 °Pu were very low, 
generally varying from 1 to 10 mBq/m 3 . 
99 Tc 
99 Tc was only analyzed for the Bornholm 
Sea, the Arkona Sea, the Kattegat and the 
Sound. Concentrations varied from 0.04 to 
3 Bq/m 3 , with the highest levels detected 
in the Kattegat. The main source of "Tc is 
inflows of contaminated waters from the North 
Sea originating from the Sellafield nuclear 
reprocessing plant. 99 Tc concentrations have 
decreased during the study period, and levels 
in the Kattegat in 2006 were 6 times lower 
than in 1999. 
3 H 
The tritium concentration in surface water was 
only reported in 1999 and 2000, when it varied 
from 1,000 to 2,000 Bq/m 3 . 
3A.6 Conclusions 
137 Cs concentrations are the main indicator 
of the radioactive status of the waters of the 
Baltic Sea. The highest concentrations during 
the report period were found in the Baltic 
Proper and the Bothnian Sea. The general 
trend is steadily decreasing. It is estimated 
that the pre-Chernobyl target value of 15 
Bq/m 3 will be reached between 2020 and 
2030. First estimates for effective half-lives 
for different parts of the Baltic Sea have 
range between 9 and 15 years. An updated 
calculation of the total inventory of 137 Cs in the 
seawater of the Baltic Sea resulted in a figure 
of 870 TBq for 2006. 
With regard to 137 Cs, the Baltic Sea is still one 
of the most contaminated areas of the World 
Ocean, even 20 years after the Chernobyl 
accident. 
References 
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