epa report on radioactivity in cigarettes

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How does radioactive material get into a cigarette?

The tobacco leaves used in making cigarettes contain radioactive material, particularly lead-210 and polonium-210. The radionuclide content of tobacco leaves depends heavily on soil conditions and fertilizer use.
Soils that contain elevated radium lead to high radon gas emanations rising into the growing tobacco crop. Radon rapidly decays into a series of solid, highly radioactive metals (radon decay products). These metals cling to dust particles which in turn are collected by the sticky tobacco leaves. The sticky compound that seeps from the trichomes is not water soluble, so the particles do not wash off in the rain. There they stay, through curing process, cutting, and manufacture into cigarettes.Lead-210 and Polonium-210 can be absorbed into tobacco leaves directly from the soil. But more importantly, fine, sticky hairs (called trichomes) on both sides of tobacco leaves grab airborne radioactive particles.
For example, phosphate fertilizers, favored by the tobacco industry, contain radium and its decay products (including lead-210 and polonium-210). When phosphate fertilizer is spread on tobacco fields year after year, the concentration of lead-210 and polonium-210 in the soil rises.