After an accident: What impact on food and humans?
Editorial review 2026
A large amount of radioactivity was dispersed into the atmosphere during the American and Soviet atmospheric tests of the 1950s and 1960s, followed by the Chernobyl accident in 1986 and, to a lesser extent, the Fukushima accident in 2011.
A small proportion of the radioactive atoms dispersed contaminated the food chain, eventually reaching our bodies and exposing us to radioactivity. What is the extent of food contamination? The extent of exposure? What are the dangers?
If we set aside short-lived radioactive atoms – such as iodine-131 – whose radioactivity disappears rapidly, the two main elements to consider, both in terms of the quantities dispersed and their lifetime, are caesium-137 and strontium-90. Of the two, caesium-137 has been studied the most because it emits gamma rays, which make its presence easy to identify (strontium does not emit gamma radiation, only beta radiation, which is more difficult to detect). More difficult to study than caesium, it is thought to be less mobile.
Although moderately radiotoxic (it remains mainly in muscle tissue), caesium raises legitimate public concern because of its long lifetime. It takes 30 years for its radioactive activity to be reduced by half.
Of the caesium atoms dispersed and slowly sinking into the soil, how many contaminate our food? How many become incorporated into our bodies? How long do they remain there?
Evolution of caesium-137 in the human body
The activity of caesium-137 in the human body has been measured near the Mol laboratory in northern Belgium for nearly half a century. Although this laboratory is far from the nuclear test sites and Chernobyl, this monitoring clearly shows the activity peak caused by these tests and the Chernobyl peak, which was approximately 4 times lower. In both cases, the decrease of caesium-137 in the human body is much faster than its natural radioactive decay, which has a half-life of 30 years.
© SCK-GEN (Source Jean Louis Genicot)
A study carried out in Belgium provided some answers. The Mol laboratory, in Belgian Flanders, measured each year for nearly half a century the radioactive activity of caesium-137 present in the human body. The laboratory is located far from the nuclear test sites of the 1950s and 1960s and from Chernobyl. These measurements provide a good indication of the exposure experienced during this period by the vast majority of the human population living far from these sites.
The activity of caesium-137, measured in becquerels (Bq), can be compared with the 8,000 Bq of natural activity in the human body, due mainly to carbon-14 and potassium-40. At the height of atmospheric nuclear testing, this activity peaked at slightly more than one tenth of natural activity (900 Bq), before falling shortly afterwards to a low level. During the Chernobyl accident in 1986, it peaked again at 3.5% of natural activity (270 Bq), before falling after 3/4 years to a level of 20 to 40 becquerels.
What explains this decrease in absorbed activity, which is much faster than radioactive decay? The presence of a radioactive element in the human body occurs through the ingestion of contaminated food, particularly agricultural products such as meat, milk, vegetables and fruit ….
Natural decrease in food contamination
From 1987, one year after Chernobyl, contamination of agricultural products resulted from the absorption through the roots of radioactive caesium present in the soil, rather than from deposits on foliage and grass as in the weeks following the accident. From then on, it was much lower and decreased steadily over the years. Today, contamination of agricultural products is 10 to 30 times lower than in 1987, and 1,000 to 10,000 times lower than immediately after the deposits of May 1986.
© Source IRSN
The decrease in the presence of caesium in the human body can be explained by natural causes, including the decrease in food contamination observed in analyses carried out in France after Chernobyl by the Institute for Radiological Protection and Nuclear Safety (IRSN). In spring 1986, the main exposures – three quarters of the total – were due to food contamination, followed by ground deposits and inhalation, well ahead of exposure due to the passage of the radioactive cloud (gamma rays). From the following year onwards, contamination of the food chain decreased continuously. Twenty years later, the annual internal doses received were 50 to 100 times lower.
In 1986, during the accident, the dispersed caesium was deposited on grass and on newly growing leaves! It was spring! Cows grazed on contaminated grass. Lettuce and broad-leaved vegetables were particularly affected. One year later, new vegetation replaced the old. From 1987 onwards, much less contamination entered food. Contamination of agricultural products occurred through the roots and no longer from radioactive deposits on leaves and grass. Root absorption of caesium-134 and caesium-137 present in the soil was an order of magnitude lower.
In 2006, the annual dose received by the French population as a result of contamination inherited from the Chernobyl accident was estimated at 0.010 mSv, the equivalent of just over one day of natural radioactivity.
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