Polonium-210, a highly radioactive isotope, accumulates in the lungs of smokers over time primarily because it is present in tobacco leaves and thus in cigarette smoke. When tobacco is grown using phosphate fertilizers, polonium-210 naturally contaminates the leaves. Upon smoking, this radioactive element is inhaled and deposits in the lung tissue, where it emits alpha particles that cause localized radiation damage.
The amount of polonium-210 that builds up in a smoker’s lungs depends on several factors, including the number of cigarettes smoked daily, the duration of smoking, and the specific polonium-210 content in the tobacco. On average, cigarette smoke contains polonium-210 in the range of picograms per cigarette, but because alpha radiation is extremely potent and damaging even in tiny quantities, even small accumulations are significant.
Polonium-210 has a half-life of about 138 days, meaning that every 4.5 months, half of the polonium present decays into stable lead-206. However, because smokers continuously inhale new polonium-210 with each cigarette, the isotope accumulates faster than it decays, leading to a steady increase in radioactive burden in lung tissue over years of smoking.
The biological impact of this buildup is severe. Alpha particles emitted by polonium-210 have very high ionizing power but very short penetration range, so the radiation damage is highly localized to lung cells. This intense localized radiation can cause DNA damage, mutations, and eventually lead to lung cancer. The risk is compounded because polonium-210 concentrates in the lungs, unlike other radioactive substances that might distribute more evenly throughout the body.
Quantitatively, the maximum allowable body burden of polonium-210 is extremely low—on the order of picograms—because of its intense radioactivity. Smokers can accumulate polonium-210 in their lungs at levels far exceeding these safety thresholds, especially with heavy, long-term smoking habits. For example, a pack-a-day smoker over many years can accumulate several nanocuries of polonium-210 in lung tissue, which translates to a significant radiation dose localized in the lungs.
This accumulation is not just theoretical; studies have shown that polonium-210 is one of the key radioactive carcinogens in tobacco smoke, contributing to the high incidence of lung cancer among smokers. The alpha radiation from polonium-210 is more damaging than many other types of radiation because it deposits energy densely along its short path, causing clustered DNA damage that is difficult for cells to repair.
The process of accumulation can be understood as a balance between intake and decay. Each cigarette introduces a small amount of polonium-210, which sticks to lung tissue. Over time, the isotope decays, but because smoking is a chronic habit, the lungs never fully clear the polonium-210 before more is added. This leads to a cumulative radioactive dose that increases with the number of cigarettes smoked and the number of years smoked.
In addition to polonium-210, other radioactive decay products of radon gas, such as polonium-218 and polonium-214, can also contribute to lung radiation exposure, but polonium-210 is particularly notable because it is directly present in tobacco leaves and smoke.
The health implications are serious. The alpha radiation from polonium-210 causes cellular damage that can initiate carcinogenesis. This is one reason why smoking is so strongly linked to lung cancer, beyond the chemical carcinogens in tobacco smoke. The radioactive component adds a layer of risk by causing direct radiation damage to lung tissue.
In summary, polonium-210 builds up in a smoker’s lungs gradually but persistently, with the amount increasing over years of smoking. The isotope’s intense alpha radiation causes localized damage that significantly raises lung cancer risk. The exact quantity depends on smoking intensity and duration, but even low levels are hazardous due to polonium-210’s extreme radioactivity and biological impact.
