Radioactivity on land and in freshwater

Chernobyl accident the largest source of contamination

Norway was heavily affected after the Chernobyl nuclear accident in 1986. This is still by far the largest source of radioactive contamination in Norwegian land areas and freshwater systems.

We find the most radioactive contamination in the areas where it rained when the air masses carrying radioactive substances from Chernobyl passed over Norway. This was mainly in northwestern parts of Eastern Norway, northern Trøndelag, and southern Nordland, but there can be wide variations even over short distances. 

The radioactive fallout contained various radioactive substances. Most substances decayed quickly and are no longer a problem.

The radioactive substance caesium-137 decays slowly, with a physical half-life of 30 years, and is therefore still present in the Norwegian environment. In the most contaminated areas of Norway, very high levels of caesium-137 were measured in fungi, lichen, reindeer and freshwater fish after the Chernobyl accident.  

Transferred into the food chains

Caesium-137 is still being absorbed from the soil by fungi and plants and transferred up the food chains to herbivores and predators. Fungi generally absorb more caesium-137 from the soil than plants. There are also large differences between species. Varying amounts of contamination and different soil characteristics also have a major bearing on how much radioactivity ends up in fungi and plants.

Wild animals and livestock that graze on rough pasture in contaminated areas usually contain more radioactive contamination than cultivated plants and livestock kept on cultivated pasture. That is why measurements and other measures are still carried out to reduce caesium-137 levels in reindeer and sheep. 

Reindeer particularly exposed to radioactive fallout

After the nuclear tests and the Chernobyl accident, particularly high levels of radioactive caesium were found in reindeer. This is because the reindeer eat mainly lichen in winter, and lichen can absorb large amounts of fallout directly from the surface.

Most of the initial contaminated lichen has now been grazed down and new lichen contains less contamination. Today, reindeer often pick up at least as much caesium-137 through plants and fungi, which are still absorbing radioactive caesium from the soil. 

The authorities have issues specific recommendations for the intake of radioactive caesium aimed at people with a high consumption of reindeer meat or other wild food products. The DSA in particular monitors the radioactivity exposure among reindeer herders from contaminated areas.

The graph below shows caesium-137 concentrations (Bq/kg fresh weight) in wild reindeer from Rondane, located in the central part of southern Norway. 

Click on the blue arrow to make the picture larger.

Vulnerable freshwater systems 

Freshwater fish can absorb large amounts of radioactive caesium, especially in nutrient-poor lakes. Although much of the contamination is carried out of the lakes and down the waterways, there are constant new inflows from run-off from the land and release of contamination stored in the sediments. 

Natural radioactivity 

Soil, plants and animals also contain various natural radioactive substances, originating mainly from bedrock. The presence of natural radioactive substances today has a far greater bearing on the radiation doses received by the general population than radioactive contamination.