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What radionuclides can be found in food?
- All foods contain natural radionuclides.
- In addition, the Chornobyl accident and the atmospheric nuclear weapons tests gave rise to artificial radionuclides in food.
- The natural radioactivity in foods is mainly caused by the potassium isotope potassium-40 and the long-lived radionuclides of the uranium-radium decay chain and the thorium decay chain.
- Among artificial radionuclides, especially caesium-137 is important for the radiation exposure to man in Germany nowadays.
The natural radioactivity in foods contributing to the radiation exposure to man is mainly caused by the potassium isotope potassium-40 and the long-lived radionuclides of the uranium-radium decay chain and the thorium decay chain. Relevant are
- uranium-238,
- uranium-234,
- radium-226,
- radium-228,
- lead-210,
- polonium-210 and
- the thorium isotopes thorium-230, thorium-232 and thorium-228.
Among artificial radionuclides, caesium-137 plays an important role as to food from forests.
How do plants and animals take up radionuclides?
Radionuclides have, in part, similar chemical characteristics as nutrients. Therefore, plants and animals also take up radioactive matter with the nutrients they need for growth. The level of specific activities in foods depends
- on the radioactivity content of the used source media (soils, water),
- on the availability of the nutrients and other substances from soil and water, and
- on other conditions at the site of the plant or animal production.
Certain plants or parts of them, such as Brazil nuts and some mushrooms species, for example wood hedgehog, enrich radionuclides to a high degree.
Some plants or parts of them, such as Brazil nuts, and some mushroom species, such as wood hedgehog, enrich certain radionuclides to a high degree.
Foods can also be radioactively contaminated via the air. From soils and rocks, for example, radon-222 gets into the atmosphere and decays into its radioactive decay products, which attach to suspended particulates. These can deposit on leaf surfaces and be taken up in the leaves. Of special importance are here the long-lived decay products of radon-222, the radionuclides lead-210 and polonium-210 of which higher activity levels, particularly occur in leafy vegetables.
In the past artificial radionuclides deposited from the atmosphere onto plant-based food and animal feed in Germany after the Chornobyl accident and the atmospheric nuclear weapons tests.
Compared with muscle meat, offal - especially livers and kidneys - has higher levels of natural radionuclides, because these organs filter the harmful substances during metabolism.
Where do the radionuclides deposit?
Natural radionuclides can also accumulate in fish and shell fish (among others in the soft tissue of clams, prawns, lobsters and shrimps), in particular lead-210 and polonium-210.
Depending on the plant species and the respective development and nutritional condition of the plant at the time of harvesting, the mineral distribution in the plant parts varies. These distributions influence the activity levels in plant-based foods. For example, the activity concentrations of the radium isotopes radium-226 and radium-228 in cereal grains are higher than those in vegetables or fruit.
Via plants and animals radionuclides get into the human food chain. The specific activity decreases in the food chain – with the exception of fish.
Potassium: Engine of the human metabolism
In the human body, a constant portion of potassium must be constantly present in order for the metabolism to work. Hence, the human body regulates its potassium content continuously. We can cover our potassium need entirely with our diet.
The element potassium contains naturally occurring 0.0117 per cent potassium-40 with an activity of 31.6 becquerel per gram of potassium. Since this share is always the same, the potassium-40 activity can be calculated from the potassium content.
Depending on age, gender and other factors, the potassium-40 activity of the human body is between about 40 and 60 becquerel per kilogram of body weight. The effective dose due to potassium-40 is on average 0.165 millisievert per year for adults and 0.185 millisievert per year for children.
Potassium is vital for all organisms and considerable amounts of it are mostly present in them:
- In plant-based foods, specific activity levels between 50 becquerel per kilogram of fresh mass in fruit and 380 becquerel per kilogram of fresh mass in ripe peas or beans can be found.
- The values are similar for products of animal origin (about 50 becquerel per litre in cow milk up to about 100 becquerel per kilogram of fresh mass in muscle meat, liver and kidneys of cattle).
- As a result of their manufacturing processes, milk powder and smoked sausage contain higher activities (above 180 becquerel per kilogram of fresh mass).
- The activity level in edible mushrooms varies between almost 10 and more than 1,000 becquerel per kilogram of fresh mass in Germany.
Caesium-137: Legacy of the Chornobyl accident and the atmospheric nuclear weapons tests
The Chernobyl accident particularly affected Southern Germany. Earlier, the atmospheric nuclear weapons tests gave rise to a widespread radioactive contamination of Germany. Today, food produced in Germany shows caesium-137 levels of only a few becquerel per kilogram of fresh mass or less.
However, some species of edible wild mushrooms and game, in particular wild boars, might show significantly higher contamination levels.
State of 2023.09.01