You are here : Home > Health effects > From exposure to toxic effects


From exposure to toxic effects

Natural and artificial exposure

Radioactivity has been naturally present on Earth since its formation. Artificial radionuclides were much more recently introduced by humans. Some radioactive elements present in the environment today are both natural and artificial in origin (e.g. carbon-14 and tritium).

Published on 18 March 2015

Humans have always been exposed to natural ionizing radiation. The resulting dose is on average 2.4 mSv per year. Since the beginning of the 20th century, the use of radioactivity in various industries and in medicine has led to the environmental release of artificial radionuclides produced by human activities. The dose attributed to artificial sources is about 1.4 mSv per year.

Natural exposure is due to

  • radiation of cosmic origin: exposure decreases in intensity as one approaches the ground. Through interaction with the elements present in the atmosphere, this radiation generates “cosmogenic” radionuclides such as carbon-14 or tritium.
  • radiation of terrestrial origin: out of 340 elements present in nature, 70 are radioactive. Sources of external and internal irradiation primarily come from radionuclides in the uranium-238 (U-238) and thorium-232 (Th-232) families, and potassium-40 (K-40), which all have very long radioactive half-lives. External exposure results from external sources and buildings. Internal exposure results from the inhalation or ingestion of radionuclides of terrestrial origin (known as “telluric”), typically referred to as internal contamination. Inhalation involves particles containing radionuclides of the U-238 and Th-232 families. Radon and its short-lived decay products are the dominant components here. The average world-wide radon exposure dose is estimated to be 1.2 mSv/year, which represents about half of the exposure to natural sources of ionizing radiation (2.4 mSv /year). Ingestion involves K-40 and radionuclides of the U-238 and Th-232 families present in the food supply.

Artificial exposure is due to

  • medical exposure: the 3 fields concerned are diagnostic radiology and interventional imaging, nuclear medicine, and radiotherapy.
  • industrial activities: coal burning, phosphate fertilizer use, and the regulated and authorized waste from nuclear facilities.
  • the consequences from the Chernobyl accident (1986) and atmospheric tests (from 1945 to 1980).

Artificial radionuclides present in the environment include cesium-137, strontium-90, plutonium isotopes, cobalt-60, iodine-131, carbon-14 and tritium.

Worldwide average contributions to public exposure from different sources
Adapted from UNSCEAR 2008 - Photo credits: L.Godart/CEA; F.Rhodes/CEA