Although there is no experimental evidence for this, the fact that the deposit dissolves in hydrogen peroxide suggests that it contains polonium in a high oxidation state.

[2] It is very difficult to oxidize polonium beyond Po(IV); for example, the only hexahalide of polonium is the hexafluoride, PoF6, and fluorine is already the most electronegative element[2] (though polonium hexaiodide was once reportedly formed in the vapour phase, it immediately decomposed).

[3] However, the difficulty in obtaining polonium trioxide and polonates (containing the PoO2−4 anion, analogous to sulfate, selenate, and tellurate) by direct oxidation of Po(IV) compounds may be due to the fact that polonium-210, while the most easily available isotope of polonium, is strongly radioactive.

Similar work with curium shows that it is easier to achieve higher oxidation states with longer-lived isotopes; thus, it may be easier to obtain Po(VI) (especially polonium trioxide) using the longer-lived polonium-208 or polonium-209.

[2] It has been suggested that Po(VI) might be more stabilized in anions such as PoF2−8 or PoO6−6, like other high oxidation states.