Naturally occurring radionuclides, primarily from the uranium and thorium decay series and potassium-40, are found in all materials in the earth's crust. These radionuclides are typically dispersed in low concentrations throughout rocks and soils and can leach into groundwater. As a result, they are more commonly found in drinking water from groundwater sources and springs compared to surface water or rainfall.

In addition to natural sources, radionuclides from human activities can also be present in food. These radionuclides can transfer from rocks and minerals in the soil and water to plants, and subsequently to animals. The doses of radionuclides people receive vary based on their concentrations in food and water, as well as local dietary habits. For instance, fish and shellfish often contain higher levels of lead-210 and polonium-210, leading to higher doses for those who consume large amounts of seafood. Similarly, people in Arctic regions who eat a lot of reindeer meat, which has high concentrations of polonium-210, receive comparatively higher doses.

Activities such as uranium mining and other extractive industries, along with the use of human-made radionuclides in industry and medicine, can also contribute to the presence of radionuclides in food and drinking water.

External joint publications

• IAEA International Basic Safety Standards (IAEA GSR-3)
• Criteria for Radionuclide Activity Concentrations for Food and Drinking Water (IAEA TECDOC-1788)
• Exposure Due To Radionuclides In Food Other Than During A Nuclear Or Radiological Emergency Part 1: Technical Material (IAEA Safety Report Series No. 114)
• Exposure Due to Radionuclides in Food Other Than During a Nuclear or Radiological Emergency Part 2: Considerations in Implementing Requirement 51 of IAEA General Safety Requirements Part 3 (International Basic Safety Standards) (IAEA TECDOC-2011)
• General Standard for Contaminants and Toxins in Food and Feed: CXS 193-1995