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3B Radionuclides In Sediments 
Jukka Mattila and Erkki Mus 
STUK, Radiation and Nuclear Safety Authority, Finland 
3B.1 Introduction 
Sediments play a significant role, when 
monitoring the state of the environment 
and radioactivity in the Baltic Sea. Many 
radionuclides tend to bind to sediment 
particles, and are accumulated in bottom 
sediments. They can therefore be analysed 
quite easily from sediment samples. At a 
proper monitoring station and in favourable 
conditions, sediment layers have stored 
continuous deposition of suspended matter 
and radionuclides for long time periods, 
which allows us to study the history and total 
amounts of certain radionuclides in sediments. 
In recent years several published articles have 
used radioactivity in sediments for monitoring 
and scientific purposes. Both natural and 
artificial radionuclides have been used, e.g. 
in estimations of sediment accumulation 
rates and in the dating of sediments (e.g. 
Jensen et al. 2003, Mattila et al. 2006). 
Radionuclides have also been used as tracers 
in intercomparisons of sediment sampling 
devices (Mus et al. 2000). The concentrations 
and amounts of transuranic elements (e.g. 
plutonium activities) in the environment of the 
Baltic Sea have been summarized during the 
reporting period (Ikaheimonen 2003). 
This report is a summary of the studies carried 
out as part of MORS-PRO on radioactivity in 
Baltic Sea sediments during the years 1999- 
2006, and is a sequel to the previous reports 
of Mus et al. (1995 and 2003). Most recently 
the report “Long-lived radionuclides in the 
seabed of the Baltic Sea” summarized the 
inventories of 137 Cs, gave new knowledge 
about artificial radioactivity in sediments, 
and took steps towards estimations of the 
amounts of natural radioactivity (e.g. 40 K and 
226 Ra activities) in the surface sediments of the 
Baltic Sea (Mus et al. 2007). 
3B.2 Material and methods 
Data has been based on the HELCOM 
database, into which the Contracting Parties 
have submitted their annual results. Additional 
data from STUK, outside of the HELCOM/ 
MORS monitoring programme, has also 
been used in the inventory calculations. The 
total number of sediment samples reported 
over the period 1999-2006 was 3,934. 
The sampling techniques used by different 
countries have been described previously 
(Mus et al. 2003). The sediment types and the 
bottom morphologies have been described 
previously in many articles (Winterhalter 1972, 
Wnterhalter et al. 1981, Nus et al. 2003). The 
methods used in the radionuclide inventories 
are described in Salo et al. (1986), Nus et al. 
(2003) and Nus et al. (2007). In general, the 
sediment inventories were based on mean 
total amounts of radionuclides in sediments 
(Bq nr 2 ) and the surface areas of different 
basins, taking into account the surface areas 
and the activities in soft and hard bottoms, 
respectively. 
3B.3 Sources of artificial radioactivity 
Over the period 1999-2006, no major events 
occurred that would have significantly 
increased artificial radioactivity in sediments in 
the Baltic Sea. In general, the main sources of 
artificial radionuclides were still the fallout from 
the Chernobyl accident in 1986 and the global 
fallout from atmospheric nuclear weapons 
testing in the 1950s and 1960s (Liming and 
llus 2003). Europe’s two nuclear reprocessing 
plants (Sellafield in the UK and La Hague 
in France) have had a minor influence on 
radioactivity in the southern Baltic Sea. 
Nuclear power plants and research reactors 
have only resulted in small local inputs to 
radionuclide concentrations in sediments 
in the vicinity of these facilities. Rivers are 
meanwhile still bringing radionuclides from 
their drainage areas into the sea. 
3B.4 Results and discussion 
The amounts of artificial radionuclides in 
bottom sediments did not increase noticeably 
during the years 1999-2006. Most of the 
artificial radioactivity was due to 137 Cs, which 
Baltic Sea Environment Proceedings No. 117