Polonium in the Earth's crust are not harmful. Polonium has been found in tobacco smoke from tobacco leaves grown with phosphate fertilizers. Because it is present in small concentrations, isolation of polonium from natural sources is a tedious process. The largest batch of the element ever extracted, performed in the first half of the 20th century, contained only (9 mg) of polonium-210 and was obtained by processing 37 tonnes of residues from radium production. Polonium is now usually obtained by irradiating bismuth with high-energy neutrons or protons. In 1934, an experiment showed that when natural Bi is bombarded with neutrons, Bi
Polonium methylated in living things to create organometallic compounds. Studies investigating the metabolism of polonium-210 in rats have shown that only 0.002 to 0.009% of polonium-210 ingested is excreted as volatile polonium-210. The median lethal dose (LD) for acute radiation exposure is about 4.5 Sv. The committed effective dose equivalent Po is 0.51 µSv/Bq if ingested, and 2.5 µSv/Bq if inhaled. So a fatal 4.5 Sv dose can be caused by ingesting , about 50 nanograms (ng), or inhaling , about 10 ng. One gram of Po could thus in theory poison 20 million people of whom 10 million would die.