The persistence of Polonium

I remain shocked, nine days after the story broke in the western media, that an ex-Russian spy was killed with Polonium-210. Steinn Sigurðsson, Derek Lowe and Paul Revere have excellent posts. In Colorado, where we usually live, radon levels in homes are generally high. When we bought a house, testing showed high Rn levels within, so the sellers had to install a system to pump out radon. The danger is actually from polonium:

If inhaled, radon decay products (polonium-218 and polonium-214, solid form), unattached or attached to the surface of aerosols, dusts, and smoke particles, become deeply lodged or trapped in the lungs, where they can radiate and penetrate the cells of mucous membranes, bronchi, and other pulmonary tissues. The ionizing radiation energy affecting the bronchial epithelial cells is believed to initiate the process of carcinogenesis. Although radon-related lung cancers are mainly seen in the upper airways, radon increases the incidence of all histological types of lung cancer.... (from the US Environmental Protection Agency).

Of course, we're talking about modest increases in risk in homes with radon above the federal standard, not death within a month as in Litvinenko's case. The health risks of polonium are discussed here.