16 
5.2 K-40 
Potassium-40 is a naturally occurring primordial 
radionuclide and forms a major source of 
radioactivity in the environment. Average activity 
concentrations of K-40 (Bq kg -1 dry weight) in the 
surface sediments (0-10 cm) of the Baltic Sea are 
shown in Figure 5. The spatial differences are due 
to the type of sediment at different sampling sta 
tions. Higher concentrations tend to occur in finer 
sediments. Typical activity concentrations of 
K-40 in soft sediments of the Baltic Sea are 
600-1 100 Bq kg -1 dry weight. 
In general, K-40 is quite evenly distributed in 
the seabed. Consequently, since samples are 
usually taken only from the surface layers of the 
sediments and the lengths of the sediment cores 
vary considerably, it is not relevant to evaluate 
the total inventory of K-40 in the Baltic Sea 
sediments based on the results from the surficial 
sediments only. In spite of that, supposing that 
the total amounts of K-40 would be equal on 
soft and hard bottoms (a not-proven starting 
hypothesis), a rough estimate results in a total 
inventory of about 8 500 TBq of K-40 in the 
0-10 cm surface layer of the Baltic Sea sedi 
ments. This is about four times higher than the 
total inventory of Cs-137 given above. 
Figure 5. 
Average activity 
concentrations of 
K-40 (Bq kg- 1 d.w.) 
in surface sediments 
(0-10 cm) at different 
sampling stations 
in the Baltic Sea at 
the beginning of the 
2000s.