Monday, January 23, 2012

Po-210 from tobacco

Possibly largest contributor (of Rn-222 or Ra-226) is tobacco which contains radioactive 210Po which emits 5.3 MeV a particles with an half life of T1/2=138.4days.
Weight-for-weight, polonium's toxicity is around 106 times greater than hydrogen cyanide (50 ng for Po-210 vs 50 mg for hydrogen cyanide). The main hazard is its intense radioactivity (as an alpha emitter), which makes it very difficult to handle safely - one gram of Po will self-heat to a temperature of around 500°C. It is also chemically toxic (with poisoning effects analogous with tellurium).
Even in microgram amounts, handling 210Po is extremely dangerous, requiring specialized equipment and strict handling procedures. Alpha particles emitted by polonium will damage organic tissue easily if polonium is ingested, inhaled, or absorbed (though they do not penetrate the epidermis and hence are not hazardous if the polonium
is outside the body).
The lethal dose (LD50) for acute radiation exposure is generally about 4.5 Sv. (Sv = Sievert which is a unit of dose equivalent). The committed effective dose equivalent 210Po is 0.51 µSv/Bq if ingested, and 2.5 µSv/Bq if inhaled. Since 210Po has an activity of 166 TBq per gram (1 gram produces 166×1012 decays per second), a fatal 4-Sv dose can be caused by ingesting 8.8 MBq (238 microcurie), about 50 nanograms (ng), or inhaling 1.8 MBq (48 microcurie), about 10 ng.

One gram of 210Po could thus in theory poison 100 million people of which 50 million
would die (LD50).
The maximum allowable body burden for ingested polonium is only 1,100 Bq (0.03 microcurie), which is equivalent to a particle weighing only 6.8 picograms. The maximum permissible concentration for airborne soluble polonium compounds is about 10 Bq/m3 (2.7 × 10-10 µCi/cm3). The biological half-life of polonium in humans is 30 to 50 days. The target organs for polonium in humans are the spleen and liver. As the spleen (150 g) and the liver (1.3 to 3 kg) are much smaller than the rest of the body, if the polonium is concentrated in these vital organs, it is a greater threat to life than the dose which would be suffered (on average) by the whole body if it were spread evenly throughout the body, in the same way as cesium or tritium.

Notably, the murder of Alexander
Litvinenko in 2006 was announced as due to 210Po poisoning. Generally, 210Po is most lethal when it is ingested. Litvinenko was probably the first person ever to die of the acute α-radiation effects of 210Po , although Irene Joliot-Curie was actually the first person ever to die from the radiation effects of polonium (due to a single intake) in the late 1950s. It is reasonable to assume that many people have died as a result of lung cancer caused by the alpha emission of polonium present in their lungs, either as a radon daughter or from tobacco smoke.

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