These various types of fallout contain several hundred different radionuclides, but only a few contribute to human exposure.
Four collectively contribute approximately 0.3 percent to the total radiation exposure. These are:
Carbon-14
Cesium-137
Zirconium-95
Strontium-90
Like some of the terrestrial sources of natural radiation, the dose from these radionuclides is generally delivered through the ingestion of the radioactivity in some foods that have been exposed to the fallout.