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 dichloride by dehalogenation of polonium tetrachloride, PoCl. Methods for dehalogenating PoCl include thermal decomposition at 300 °C, reduction of cold, slightly moist PoCl by sulfur dioxide; and heating PoCl in a stream of carbon monoxide or hydrogen sulfide at 150 °C. PoCl dissolves in dilute hydrochloric acid to give a pink solution, which autoxidises to Po(IV). PoCl is rapidly oxidised by hydrogen peroxide or chlorine water. Addition of potassium hydroxide to the pink solution results in a dark brown precipitate – possibly hydrated PoO or Po(OH) – which is rapidly oxidised to Po(IV). With dilute nitric acid, PoCl forms a dark