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  stations. ­
  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  sediments. ­
  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.