Tobacco farmers use fertilizer to help their crops grow. These fertilizers contain a naturally-occurring radionuclide, radium. Radium radioactively decays to release radon gas, which then rises from the soil around the plants. As the plant grows, the radon from fertilizer, along with naturally-occurring radon in surrounding soil and rocks, cling to the sticky hairs on the bottom of tobacco leaves. Radon later decays into the radioactive elements lead-210 and polonium-210. Rain does not wash them away. Polonium-210 is an alpha emitter and carries the most risk.

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