Current status and trends for radioactive substances

Pollution
Typography

The issue of present and potential radioactive contamination in the marine environment has received considerable attention in Norway. The Norwegian marine monitoring programme (RAME) focuses on monitoring of radioactivity both in coastal areas and in the open sea. This programme also includes monitoring of discharges from Norwegian sources and collection of discharge data relevant for the long-range transport of radionuclides from various sources (NRPA, 2011).

 

Overall, the activity concentrations of such radionuclides as 99Tc, 90Sr, 137Cs, 239+240Pu, 241Am and 226Ra in the Barents Sea are similar or slightly lower than have been observed in recent years. Presently, a general tendency to decrease is indicated for all the radionuclides. This can be explained by reduced discharges, radioactive decay and other processes such as sedimentation and dilution (NRPA, 2011).

Radioactivity in sea water and sediments

The main source of 99Tc in Norwegian waters is liquid discharge from the reprocessing plant at Sellafield in UK. From the Irish Sea, 99Tc is transported by ocean currents to the North Sea and via the Norwegian Coastal Current up to the Barents Sea. The activity concentration of 99Tc in the Barents Sea in 2008 and 2009 ranged from 0.03 to 0.44 Bq m-3. The highest concentrations were found in coastal water. The activity concentrations found in the North Sea and the Barents Sea are generally lower than those observed in 2002, 2003 and 2005 (NRPA, 2005; NRPA, 2007). The reason for this is the reduced discharge of 99Tc from Sellafield (Fig. 4.4.2.3).

Strontium-90 is a fission product with a physical half-life of 29 years. Similar to 99Tc, 90Sr is a conservatively behaving element in the marine environment. The main sources of 90Sr in the Barents Sea are discharge of liquid waste from reprocessing plants (mainly Sellafield), fallout from atmospheric nuclear weapons tests conducted mainly in the 1950s and 1960s and outflow of water from the Baltic Sea. In the Barents Sea the activity concentration in surface water ranged from 0.7 Bq m-3 to 1.5 Bq m-3. Results show that the activity concentration of 90Sr in sea water is slowly decreasing. One explanation for this is the reduced discharges from Sellafield over the last 10 years (Fig. 4.4.2.4a,b).

Figure 4.4.4.3. Annual liquid discharge of 90Sr from Sellafield and Cap de la Hague in the period 1999 to 2009 (data from OSPAR, NRPA, 2011).

Figure 4.4.4.3. Annual liquid discharge of 90Sr from Sellafield and Cap de la Hague in the period 1999 to 2009 (data from OSPAR, NRPA, 2011).

 

Figure 4.4.2.4a Activity concentration (Bq m-3) of 99Tc in surface water samples collected in the Barents Sea in 2008 (NRPA, 2011).

Figure 4.4.2.4a Activity concentration (Bq m-3) of 99Tc in surface water samples collected in the Barents Sea in 2008 (NRPA, 2011).

 

Figure 4.4.2.4b Activity concentration (Bq m-3)90Sr (b) in sea water samples collected in the Barents Sea in 2009 (NRPA, 2011).

Figure 4.4.2.4b Activity concentration (Bq m-3); 90Sr (b) in sea water samples collected in the Barents Sea in 2009 (NRPA, 2011).

Caesium-137 is a fission product with a half-life of 30 years. The main sources of 137Cs in the Barents Sea are fallout from atmospheric nuclear weapons tests in the 1950s and 60s, outflowing water from the Baltic Sea and 137Cs remobilised from the Irish Sea sediments. Runoff from land, from the areas with the highest Chernobyl fallout can also contribute locally in coastal water. Like 99Tc and 90Sr, 137Cs is also a conservatively behaving radionuclide in sea water. Observed levels of 137Cs in surface water in the Barents Sea in 2009 showed an activity concentration in the range from 1.5 to 2.3 Bq m-3. This is generally similar or lower than the activity concentrations observed in the same area in the period 2002 to 2006. Cs-137 has also been analysed in surface sediments (upper 2 cm layer) from the Barents Sea and showed activity concentrations between 0.8 and 7.0 Bq kg-1 (d.w.) (Fig. 4.4.2.5a,b).

Figure 4.4.2.5a Activity concentration (Bq m-3) of 137Cs in surface water samples collected in the Barents Sea in 2009 (NRPA, 2011).

Figure 4.4.2.5a Activity concentration (Bq m-3) of 137Cs in surface water samples collected in the Barents Sea in 2009 (NRPA, 2011).

 

Figure 4.4.2.5b Activity concentration (Bq m-3) of 137Cs in surface water (a) and in sediment (Bq kg -1 d.w.)(b) samples collected in the Barents Sea in 2009 (NRPA, 2011).

Figure 4.4.2.5b Activity concentration (Bq m-3) of 137Cs in surface water (a) and in sediment (Bq kg -1 d.w.)(b) samples collected in the Barents Sea in 2009 (NRPA, 2011).

Plutonium-239 (a half-life of 24 110 y) and 240Pu (a half-life of 6 563 y) belong to the transuranium elements. The behavior of plutonium in the marine environment is complex due to its different possible oxidation states. The main sources of 239+240Pu in the Northern Norwegian marine waters are the global fallout from atmospheric nuclear weapons tests in the 1950s and 1960s and remobilised plutonium from the Irish Sea sediments. Observed levels of 239+240Pu in the Barents Sea in 2008 and 2009 ranged from 1.4 to 12.4 mBq m-3 (Fig. 4.4.2.6a,b). The activity concentrations of 239+240Pu are similar to those found in 2002 and 2005 (NRPA, 2011).

Figure 4.4.2.6a Activity concentration (mBq m-3) of 239+240Pu in surface water and (a) and 241Am in sea water (b) samples from the Barents Sea in 2008 (NRPA, 2011).

Figure 4.4.2.6a Activity concentration (mBq m-3) of 239+240Pu in surface water and (a) and 241Am in sea water (b) samples from the Barents Sea in 2008 (NRPA, 2011).

 

Figure 4.4.2.6b Activity concentration (mBq m-3) of 239+240Pu in surface water and (a) and 241Am in sea water (b) samples from the Barents Sea in 2008 (NRPA, 2011).

Figure 4.4.2.6b Activity concentration (mBq m-3) of 239+240Pu in surface water and (a) and 241Am in sea water (b) samples from the Barents Sea in 2008 (NRPA, 2011).

Americium-241 belongs to the transuranium elements and has a physical half-life of 432 years. Main sources of 241Am in the environment are fallout of 241Pu from nuclear weapon tests in the 1950s and 1960s and the discharge of 241Am and 241Pu from reprocessing plants. The measured activity concentrations of 241Am in the Barents Sea in 2008 and 2009 ranged from 1.0 to 9.0 mBq m-3 (Fig. 4.4.2.7). The observed levels of 241Am are similar to those found in 2002 and 2005 (NRPA, 2011). Radium-226 is a naturally occurring radionuclide with a physical half-life of 1 600 years. In the marine environment 226Ra is naturally supplied from both the sediments and by river water to the oceans. The activity concentrations of 226Ra observed in the Barents Sea in 2009 ranged from 0.9 to 2.4 Bq m-3. This is similar to those found in 2005 in the same area (NRPA, 2006; NRPA, 2011).

Figure 4.4.2.7 Activity concentration (Bq m-3) of 226Ra in surface water from the Barents Sea in 2009 (NRPA, 2011).

Figure 4.4.2.7 Activity concentration (Bq m-3) of 226Ra in surface water from the Barents Sea in 2009 (NRPA, 2011).

 

Radioactivity in biota

99Tc, 137Cs and 239+240Pu in seaweed

Seaweed is a useful bioindicator for accumulation of radioactive substances in the marine environment. It has a high ability to concentrate radionuclides from the sea water and is easy accessible in most coastal areas. Fucus vesiculosus has been widely used as a bioindicator for 137Cs and 99Tc. The accumulation of 137Cs in brown algae is, however, not as pronounced as for 99Tc. The uptake of 137Cs also depends on the salinity of the surrounding sea water, with higher uptake at lower salinities (Carlsson and Erlandsson, 1991).

Fucus vesiculosus collected at the permanent coastal stations along the Norwegian coastline in 2008 and 2009 showed an activity concentration of 99Tc in range from 35 to 115 Bq kg-1 (d.w.). For most stations the levels were lower in 2008 and 2009 compared to observed levels in the period 2002 - 2007. The monitoring results showed that the levels of 99Tc in seaweed have decreased at most sampling sites due to the reduced discharge of 99Tc from Sellafield (NRPA, 2011). The activity concentration of 137Cs in Fucus vesiculosus sampled at the coastal stations in 2008 and 2009 was in the range from < 0.2 to 3.3 Bq kg-1 (d.w.). Data from monthly monitoring at Utsira indicates that the levels of 137Cs in seaweed are slowly decreasing. One can also see a slowly decreasing trend in the activity concentration of 239+240Pu in the seaweed samples collected at Utsira in period from 1980 to 2009 (NRPA, 2011).

137Cs in fish, molluscs and crustacenas

Different types of fish and other commercially important species have been sampled in the Barents Sea since 1990s. The activity concentration of 137Cs in cod caught in two areas of the Barents Sea in 1990s was below 1 Bq kg-1 (w.w.), samples collected in recent years (2008 and 2009) showed levels below 0.5 Bq kg-1 (w.w.). Overall, the monitoring results of fish for period 1992-2009 showed a slightly decreasing trend of 137Cs concentration in fish species from the Barents Sea and indicated low activity concentrations in general. Cs-137 activity concentrations in crustaceans and mollusks caught in Norwegian marine waters in 2008 and 2009 were below 1.5 Bq kg-1 (w.w.).

References

AMAP. 2004. AMAP Assessment 2002: Persistent Organic Pollutants in the Arctic. Arctic Monitoring and Assessment Programme (AMAP), Oslo, Norway. xvi +310 pp.

Carlsson L. and Erlandsson B., 1991 Carlsson L, Erlandsson B. Effects of salinity on the uptake of radionuclides by Fucus vesiculosus L. Journal of Environmental Radioactivity 1991; 13: 309-322.

NRPA, 2005. NRPA. Radioactivity in the marine environment 2003. Results from the Norwegian National Monitoring Programme (RAME). StrålevernRapport 2005:20. Østerås: Norwegian Radiation Protection Authority, 2005.

NRPA, 2006. NRPA. Radioactivity in the marine environment 2004. Results from the Norwegian National Monitoring Programme (RAME). StrålevernRapport 2006:14. Østerås: Norwegian Radiation Protection Authority, 2006.

NRPA, 2007. NRPA. Radioactivity in the marine environment 2005. Results from the Norwegian National Monitoring Programme (RAME). StrålevernRapport 2007:10. Østerås: Norwegian Radiation Protection Authority, 2007.

NRPA, 2011. NRPA. Radioactivity in the marine environment 2008 - 2009. Results from the Norwegian National Monitoring Programme (RAME). StrålevernRapport 2011:4. Østerås: Norwegian Radiation Protection Authority, 2011.