17 
5.3 Sr-90 
Traditionally, strontium-90 has been, together with 
Cs-137, the other intensively monitored artificial 
radionuclide in radioecological studies because 
it is one of the most important fission products 
and its half-life is almost as long (28.5 years) as 
that of Cs-137. In the atmospheric weapons tests 
during the 1950s and 1960s, the dominant fallout 
nuclides were Cs-137 and Sr-90 in an activity ratio 
of about 1.6. Consequently, Sr-90 was intensively 
monitored in the environment after that. In recent 
years, the frequency of analysis of strontium 
has been significantly reduced. One reason is 
the laborious and time-consuming analytical 
method for Sr-90; however, in addition, there is 
less interest in strontium because its share in the 
Chernobyl fallout was much smaller than that of 
Cs-137. The total input of Sr-90 from the Cherno 
byl fallout into the Baltic Sea area was estimated 
at 80 TBq (decay corrected to 1991), while it was 
4 100-5 100 TBq for Cs-137 (Nies et al„ 1995). 
Although the acquisition of recent data on Sr-90 
in the Baltic Sea sediments was set as a target 
for the Sediment Baseline Study, relatively few 
results were reported to the database during the 
project. Furthermore, due to the wide diversity of 
the data reported (e.g., the length of the sediment 
props analysed varied from 3 cm to 40 cm), it was 
difficult to estimate the total current inventory of 
Sr-90 in the seabed of the Baltic Sea. Typical total 
amounts of Sr-90 in sediments were from about 
50 Bq nr 2 to 200 Bq nr 2 . A rough estimate of the 
total inventory was calculated as 26 TBq, which is 
about two times higher than that (12 TBq) given by 
Salo et al. (1986) for the beginning of the 1980s. 
This seems to be in agreement with the deposition 
values and the concentrations in sediments. 
5.4 Tc-99 
The concentrations of technetium-99 were low in 
the sediments of the Baltic Sea. In four samples 
analysed, the activity concentrations of Tc-99 in 
surface layers of the sediments (0-10 cm) varied 
between 0.040 Bq kg -1 and 1.3 Bq kg -1 d.w. The 
highest value was in the Belt Sea and the lowest 
in the Gulf of Finland. 
Long-lived radionuclides in the seabed of the Baltic Sea