The human body always contains radioactive substances

Radioactive substances enter the human body in food, drinking water and inhaled air. The body always contains naturally occurring radioactive materials. In addition, we receive cesium-137 originating from the Chernobyl accident in food.

Potassium-40 is an example of naturally occurring radioactive materials in the human body. Naturally occurring potassium always includes a standard portion of the radioactive potassium-40 isotope. An adult person usually contains 3,000–6,000 becquerels (Bq) of potassium-40. In addition, naturally occurring uranium and thorium from the bedrock, as well as their decay products, are found in the human body. The best known and, with regard to the radiation exposure of Finns, the most important decay product is radon, a substance that belongs to the decay series of uranium. Radioactive substances enter the human body in food, drinking water and inhaled air.

Long-lived cesium-137 (half-life 30 years) and strontium-90 (28 years), originating from the fallout generated during the nuclear weapon testing era, have been transferred to the human body in food.  As a consequence of the Chernobyl accident, people are still receiving cesium-137 in food. Cesium-134, originally also present in the fallout, has nearly disappeared by now, due to its short half-life (two years). Immediately following the accident, Finns received small amounts of radioactive iodine-131 in milk and inhaled air. The amounts of radioactive materials released from normally functioning nuclear power plants are so low that they are insignificant for people.

Cesium-137 activity in different contro groups in Finland

Cesium-137 activity in a control group representing population in the Helsinki Capital Region, reindeer breeders in Northern Lapland and heavy users of food from the nature in Päijät-Häme. Cesium concentrations preceding 1986 originate from the fallout resulting from nuclear weapon testing performed in the atmosphere.

STUK has been following the exposure of Finns since the 1960s by carrying out direct measuring of people. People in the control group from the Helsinki Capital Region have been measured with equipment installed in the STUK laboratory in Helsinki. The reindeer breeders in Lapland and heavy users of natural produce in Päijät-Häme have been measured with equipment installed in a lorry.  The figure above shows how the effect of nuclear weapon testing performed in the atmosphere differs from the effects of the Chernobyl accident.

The fallout from nuclear weapon testing, received over a longer period of time, was distributed evenly throughout Finland, but there is a big difference in the results between the Helsinki group and the reindeer breeders in Lapland. The difference is due to a different diet. In the rugged nature of Lapland, the lichen–reindeer–human food chain is a strong enricher of cesium. The fallout from Chernobyl, on the other hand, was distributed very unevenly. Lapland and the population-rich Capital Region received the lowest amounts. The Päijät-Häme region received more fallout and the radiation exposure of heavy users of natural produce in the region is higher than the exposure of people living in other parts of Finland. However, in Finland as a whole, the radiation dose resulting from the Chernobyl accident constitutes a very small percentage of the total annual dose.

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  • Maarit Muikku / Head of Laboratory