Cigarettes contain trace amounts of the radioactive isotope polonium-210, which contributes to the radiation dose inhaled by smokers. Polonium-210 is a naturally occurring alpha emitter with a half-life of about 138 days, and it is found in tobacco leaves primarily due to the uptake of radon decay products from the soil and air. When tobacco is smoked, polonium-210 attaches to the smoke particles and is inhaled deep into the lungs, where it emits alpha radiation that can damage lung tissue.
The amount of polonium-210 inhaled per cigarette is very small in absolute mass but significant in terms of radioactivity and biological effect. Estimates of radiation exposure from polonium-210 in cigarette smoke vary widely, but heavy smokers may inhale radiation doses ranging from about 100 microsieverts (µSv) up to 160 millisieverts (mSv) over time, depending on smoking intensity and cigarette brand. To put this in perspective, 1 millisievert is 1,000 microsieverts, so the upper estimates represent a substantial cumulative radiation dose concentrated in lung tissue.
Polonium-210’s specific activity is extremely high—about 166 terabecquerels per gram—meaning even picogram (trillionth of a gram) quantities deliver intense alpha radiation. The alpha particles emitted by polonium-210 cannot penetrate the skin but are highly damaging when emitted inside the body, especially in the lungs where they can cause DNA damage and increase cancer risk. The alpha radiation from polonium-210 in cigarette smoke is considered one of the factors contributing to the high incidence of lung cancer in smokers.
To understand the scale, the maximum allowable body burden for ingested polonium-210 is only about 1.1 kilobecquerels, corresponding to a mass of roughly 7 picograms. Cigarette smoke delivers polonium-210 in amounts that, while small, accumulate with repeated smoking and concentrate in lung tissue, particularly in the bronchial epithelium. This localized concentration means the radiation dose to lung cells is much higher than the average dose to the whole body.
The process by which polonium-210 gets into tobacco involves radon gas decay products settling on tobacco leaves during growth and curing. Radon-222 decays to lead-210, which then decays to polonium-210. Because tobacco plants grow close to the ground and are often cured in enclosed spaces, they accumulate these radioactive particles. When smoked, the polonium-210 attached to tar particles is inhaled and deposited in the lungs.
The radiation dose from polonium-210 in cigarettes is part of the overall radiation exposure smokers receive, which also includes other radioactive elements like lead-210 and radon progeny. However, polonium-210 is particularly dangerous due to its alpha emissions and its ability to lodge in lung tissue. The alpha particles cause dense ionization tracks that can break DNA strands and initiate carcinogenesis.
Quantitatively, a single cigarette can deliver a polonium-210 activity on the order of a few millibecquerels to tens of millibecquerels. While this seems minuscule, the cumulative effect over years of smoking hundreds or thousands of cigarettes results in a significant radiation burden. For example, a pack-a-day smoker might inhale polonium-210 radiation doses that are comparable to or exceed those from some occupational radiation exposures.
The biological impact of inhaled polonium-210 is exacerbated by its chemical behavior. Polonium is a heavy metal that tends to bind to lung tissue, especially the mucous membranes and bronchial epithelium. This retention prolongs the exposure time of lung cells to alpha radiation, increasing the likelihood of mutations and cancer development.
In addition to lung cancer, polonium-210 exposure from smoking may contribute to other respiratory diseases due to chronic radiation damage and inflammation. The radiation dose from polonium-210 is highly localized, so while the whole-body dos
