By Hilde Elise Heldal
When Sellafield increased emissions of Tc-99 in 1994-95, the news attracted a lot of attention in Norway. At the end of the 1990s, levels of Tc-99 in sea water, kelp and lobster along the Norwegian coast started to increase. High levels of emissions continued until 2003, but since 2004 emissions have been back down at the pre-94 levels.
As a result of this, we have been expecting to see a reduction of T-99 levels in the marine environment. Levels of T-99 are still significantly above pre-94 levels, but samples taken in 2006 show that levels are on their way back down. Last week there was a radioactive leak at the facility. (external link) Provided that the leak was as small as has been claimed, we do not expect it to show up in our readings.
Old Norwegian kelp
Lobster and kelp have been notable as taking up more Tc-99 than other marine organisms. The monitoring of Tc-99 levels has therefore concentrated on them. In lobster collected from Værlandet in the county of Sogn og Fjordane we have observed a reduction in Tc-99 concentrations from 2004 to 2006, although there is quite a lot of variation in concentration levels from year to year.
The Norwegian Radiation Protection Authority and Institute for Energy Technology have long time-series of Tc-99 levels in kelp from Hillesøy and Utsira respectively. Both of the time-series showed a reduction in concentration levels from 2005 to 2006.
Old annual shoots of Norwegian kelp may contain relatively high concentrations of Tc-99. (Photo: Hilde Elise Heldal)
In 2005-06 more detailed studies were carried out at the Institute of Marine Research on the distribution of Tc-99 in Norwegian kelp (Ascophyllum nodosum). The Tc-99 concentration in annual shoots increases with the age of the shoot. This means that older annual shoots of Norwegian kelp may still contain relatively high concentrations of Tc-99.
In a study of the distribution of Tc-99 in the ecosystem around Norwegian kelp, we found that snails that graze directly on the kelp contain higher concentrations of Tc-99 than snails that live on rocks close to Norwegian kelp. In other words, animals that graze on Norwegian kelp take up Tc-99.
Not above the intervention level
We have never found concentrations in marine organisms along the Norwegian coast that exceed the EU Food Intervention Level for nuclear accidents, which is 1250 Bq/kg. We do not believe that the Tc-99 pollution has constituted a health hazard to seafood consumers. However, the pollution has caused concern amongst both Norwegian consumers and overseas importers of Norwegian seafood. It is therefore good to see that the levels are now falling.
Waiting for more recent data
The recently released report presents data from the national monitoring programme for radioactive pollution in Norwegian coastal and offshore areas (RAME) (external link). The programme is coordinated by the Norwegian Radiation Protection Authority, and the Institute of Marine Research is a major contributor. The report also presents monitoring data for other radioactive elements in the marine environment (caesium-137, strontium-90, plutonium-239+240, americium-241 and radium-226). The report shows that the levels of all of these elements have been fairly stable in recent years. Analysing several of these elements is very time-consuming, and it will therefore take some time before we are able to present the data in a final report.
In 2008, the Institute of Marine Research took samples of sea water from the North Sea and Barents Sea, as well as samples of lobster, kelp and sea water from Værlandet. We have already started analysing these samples, and the results will be available in the spring of 2009.