Cigarettes contain a small but significant amount of radioactive material, primarily polonium-210, which emits alpha radiation. This radioactive contamination comes from the tobacco plant absorbing radioactive elements from the soil and from the use of certain fertilizers. The radiation dose a smoker receives from polonium-210 in cigarettes can be surprisingly high compared to everyday background radiation sources, including cosmic rays.
To understand the comparison, it’s important to first grasp what cosmic rays are. Cosmic rays are high-energy particles from outer space that constantly bombard the Earth’s atmosphere. When these particles interact with the atmosphere, they produce secondary radiation, including muons, neutrons, and gamma rays, which reach the surface. The average person receives about 0.3 millisieverts (mSv) per year from cosmic radiation at sea level, though this can vary with altitude and latitude.
Now, looking at cigarettes, the radioactive isotope polonium-210 is the main source of radiation. Polonium-210 emits alpha particles, which are highly ionizing but have very low penetration power, meaning they can cause significant damage if inhaled or ingested but do not penetrate the skin. When a smoker inhales cigarette smoke, polonium-210 particles lodge in the lungs, delivering localized radiation doses.
Estimates of the radiation dose from smoking vary, but heavy smokers can receive an annual radiation dose to the lungs ranging from about 100 microsieverts (µSv) up to 160 millisieverts (mSv). To put this in perspective:
– **100 µSv (microsieverts)** is about one-third of the average annual dose from cosmic rays at sea level.
– **160 mSv (millisieverts)** is over 500 times the average annual cosmic ray dose.
This wide range depends on smoking intensity and cigarette brand, but even at the lower end, the radiation from smoking is comparable to or exceeds the cosmic ray dose a person receives annually.
Why is this significant? Cosmic rays expose the whole body relatively uniformly, but the radiation from polonium-210 in cigarettes is concentrated in the lungs, increasing the risk of lung cancer. Alpha particles cause dense ionization tracks in tissues, leading to DNA damage and mutations. This localized exposure is far more harmful than the same dose spread over the entire body.
In summary, while cosmic rays provide a steady, low-level background radiation dose to everyone, the radiation dose from smoking cigarettes can be much higher in the lungs due to polonium-210. A heavy smoker’s lungs may receive hundreds of times more radiation annually from cigarette smoke than from cosmic rays. This adds a significant radiation-related health risk on top of the chemical toxins in tobacco smoke.
This comparison highlights an often overlooked danger of smoking: it is not just chemical toxicity but also radioactive contamination that contributes to its harmful effects. The radiation dose from cigarettes is unique because it delivers alpha radiation directly to lung tissue, which is far more damaging than the low-level external radiation from cosmic rays.
