Polonium is a chemical element discovered in 1898 by Marie and Pierre Curie, which separated it from the pitchblende, few years before isolating radium. It is a very rare element, because of the very short half-life of all its isotopes. In uranium ores, polonium is found at about 100 mg per ton (1 part in 1010).
Polonium has been found in tobacco smoke from tobacco leaves grown with phosphate fertilizers. This element has 25 known isotopes, from 194 to 218, all of which are radioactive. 210Po is the most widely available. Only about 100 grams are produced each year, making polonium exceedingly rare. Polonium-210 is an alpha emitter that has a half-life of 138.376 days. A milligram of 210Po emits as many alpha particles as 5 grams of radium.
Because it emits many alpha particles, which are stopped within a very short distance in dense media and release their energy, 210Po has been used as a lightweight heat source to power thermoelectric cells in satellites.
A 210Po heat source was also used in each of the Lunokhold rovers deployed on the surface of the Moon, to keep their internal components warm during the lunar nights. "Polonium 210 is a radio isotope that is, basically, an isotope that's not used in biomedical research. It's an isotope that meets, at a very short range, alpha particles and these alpha particles are, basically, very damaging to cellular tissue." said Colin Hill from University of Southern California. Current spectroscopy measure gamma rays, that travel further than alpha rays, that's why 210Po is more difficult to find and identify.
Alpha particles emitted by polonium will harm cells easily if polonium is ingested, inhaled, or absorbed (though they do not penetrate the skin and hence are not hazardous if the polonium is outside the body). "It's unfortunately if you ingest it or inhale it, it will spread all over the body. It's an unusually rated nucleotide that doesn't particularly go to one part of the body. The alpha particles are emitted at a very short range; that means they don't travel very far before they give up their energy. When they do that, they actually are going to hit the DNA in the cell and damage it directly and actually, this gives enough of an energy that will kill the cell directly so if this stuff is distributed around the body, it's going to kill cells all over the body." added Hill.
"Depending on the size of the dose, what's going to happen is that cells that are dividing in the body include the mucosa in the mouth, in the intestines, the lining of the intestines, blood cells. All of these cells are going to start dying so you're going to start to get symptoms of diarrhea, saunas in the mouth or you're going to start to get lethargy, tiredness, anemia, loss of blood cells."
The maximum allowable body burden for ingested polonium is only 6.8 picograms. The biological half-time of polonium in humans is 30 to 50 days. The target organs for polonium in humans are the spleen and liver and the chronic intoxication translates by cancer.
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.
But the lethal dose for acute radiation exposure is generally about 50 nanograms (ng) for ingestion, or inhaling about 10 ng. One gram of 210Po could theoretically poison 100 million people. "All you need is something in the range of 50 nanograms, if you're ingesting it, to kill a person over a course of 2 or 3 weeks. That's less than you could put on the head of a pen it's an extremely small amount."
Probably the first person ever to die of the acute alpha radiation effects of poisoning with Polonium-210 is Alexander Litvinenko (photo), former KGB spy. He probably ingested Polonium on November 1, 2006 leading to his death on November 23, 2006. Irene Joliot-Curie, daughter of Pierre and Marie Curie is also suspected to have died from the radiation effects of Polonium (due to a single intake) in the late 1950's. And perhaps many people have been dying due to lung cancer provoked by the alpha emission of polonium present in their lungs from tobacco smoke.