Who is at risk?

High-Risk Groups

Epidemiological studies have shown that fetuses, infants, children, and pregnant and lactating women are most in need of protection from radioiodine exposure and most likely to benefit from potassium iodide.

• Fetuses. Radioiodine can cross the placenta and enter the fetal thyroid.
• Children. Infants and children are more vulnerable to the potentially harmful effects of radioiodine than adults because their thyroids concentrate iodine more actively on an organ-weight basis and are biologically more sensitive.
• Pregnant and Lactating Women. Lactating women can concentrate radioiodine in their milk and transfer it to their nursing infants.

Where You Live Matters

After an incident at a nuclear reactor, a plume–a cloud of airborne radioactive material that is transported from a nuclear or radiological source in the direction of the prevailing wind–moves across the area. During the plume phase, the thyroid can be exposed if radioiodine is present and inhaled.

Factors such as location and weather can affect the extent to which a population is exposed to radioiodine. Wind speed, direction, variability, and vertical dispersion can alter how fast, far, and wide radionuclides are transported in the air. Under very stable atmospheric conditions, there is little dispersion of the plume, so the radionuclide concentration is high. Only those people in the direct path of the plume will be in immediate danger. Just like smoke, a radioactive plume dissipates as it moves away from its source, which quickly decreases the concentration of radioactive materials within the plume.