Some radioactive substances are absorbed by plants and animals from the soil or water that they live in. In this way, these substances also enter the food chains that make up our diet.
Natural radioactivity in food
Natural radioactivity has always been present in the environment, and hence in our food. Most of these substances originate from bedrock but are transferred into the food chains. All of us therefore receive a certain radiation dose from the food we eat.
Contamination from artificial radioactivity
The Chernobyl accident in 1986 is the main source of radioactive contamination in Norwegian food. The radioactive substance caesium-137 has been the most problematic in the long term, as it has a half-life of 30 years and is readily absorbed into the food chains.
The vast majority of foods now contain low levels of caesium-137. Seafood generally has a very low content. Most agricultural products also have low levels.
Wild food products such as game, freshwater fish, mushrooms and berries from areas heavily affected by contamination from the Chernobyl accident usually contain more radioactive caesium than agricultural products. This is because fertilising and ploughing leads to less radioactive caesium being absorbed by plants on cultivated land than on nutrient-poor uncultivated land. Livestock grazing on contaminated uncultivated land, including sheep and semi-domesticated reindeer, also contain higher levels of radioactive caesium.
Because most people eat only small amounts of wild food products compared to other foods, this has little effect on the radiation dose for most people. For people with very high consumption of semi-domesticated reindeer, game and other wild foods from contaminated areas, the government has issues specific recommendations on the intake of radioactive caesium.
Maximum permitted levels and measures to reduce radioactive contamination in food
After the Chernobyl accident, the Norwegian authorities introduced maximum permitted levels for radioactive caesium. The maximum permitted levels apply only to food for sale:
|Category||Maximum permitted level for radioactive caesium (Bq/kg)|
|Milk and dairy products and food for infants and young children||370|
|Meat and meat products of semi-domesticated reindeer, game and wild freshwater fish||3000|
In the first few years after the accident, large amounts of meat and milk had to be disposed of because they were above the maximum permitted levels. Various types of measures were therefore quickly developed to reduce the levels in meat and milk to prevent them from exceeding the maximum permitted levels and having to be disposed of.
In the reindeer herding and sheep farming sectors, measures are still needed in some areas to prevent caesium-137 levels from exceeding the maximum permitted levels and to limit exposure for vulnerable groups. Every year, sheep herds in selected municipalities must be brought down onto cultivated land and given clean feed for a certain number of weeks before they can be slaughtered, in order to bring the levels in the meat down below the maximum permitted level.
The graph below shows the number of sheep given clean feed.
Click on the blue arrows to make the picture larger.
Health risk associated with radioactivity in food
The substances that contribute most to the radiation dose from food in the population include potassium-40, polonium-210, carbon-14 and lead-210. In some instances, radon can provide a significant dose contribution through the intake of drinking water from groundwater sources.
The average radiation dose of the population in Norway is estimated at 5.2 mSv per year from all types of natural and artificial sources. The radiation dose from the intake of natural radioactivity in food and drink makes up approximately 10 % of this dose. Nowadays, radioactive contamination in food has very little effect on the radiation dose for most people, and accounts on average for less than 1% of the total radiation dose.
People who eat very large amounts of wild food products from the areas that were most contaminated after the Chernobyl accident can still receive a significant part of their radiation dose from food. In practice, these are mostly reindeer herders with a traditional very high intake of reindeer meat.
- Report from the Norwegian Scientific Committee for Food Safety: Risk assessment of radioactivity in food.