Exposure
Inhalation of the isotope may occur during occupational exposure or while smoking cigarettes, since atmospheric ²¹⁰Po settles onto tobacco leaves.³ Deposition in the lung depends on particle size and solubility. The majority of particles are removed from the respiratory tract by mucociliary clearing and then subsequently swallowed. At that point, ²¹⁰Po is reintroduced to the body as ingesta.⁵

Ingestion may also occur while eating in contaminated areas or through consumption of contaminated foodstuffs. For example, caribou meat, a dietary staple in northern Canada, has a high concentration of ²¹⁰Po due to its presence in the lichens they eat.⁶ In general, only a small fraction of the isotope is absorbed following ingestion, with as much as 90% being quickly excreted from the body in the feces.³

Dermal or parenteral exposure to ²¹⁰Po is unlikely. While dust or aerosolized particles may deposit on skin and clothing, alpha particles cannot penetrate these barriers since most of their energy is lost on impact. The particles can, however, enter through open wounds and absorb subcutaneously.⁷ Parenteral access does not typically occur accidentally or occupationally, but is a common route of entry in medical procedures and in clinical research.²

Once ²¹⁰Po is taken in, the whole body is essentially targeted. The administered dose and individual tissue sensitivity determines the extent of damage throughout the body.² Unlike most heavy metals, ²¹⁰Po accumulates in soft tissue rather than bone.⁸ There is species variation with regard to distribution, but for the most part, the kidneys, liver, and spleen contain the highest concentrations. In blood, the majority of the isotope is found in the red blood cells, bound to hemoglobin. Its binding to the globin component rather than heme indicates an affinity for proteins. Very little is found in aggregates with plasma or erythrocyte lipids. Deposition seems to depend somewhat on route of entry, with a much higher concentration in the blood after oral administration and in the kidney and spleen after intravenous administration.⁸

²¹⁰Po is primarily eliminated in feces and urine. Older data asserts that following oral administration, 90% of the ingested isotope is rapidly excreted in the feces.⁸ This conflicts with newer experimental findings which put the fecal excretion rate at 55–69% and renal elimination at 20–38%. The newer study also found that the biological half-life of polonium-210 varies from 15–50 days depending on the species.⁵ The isotope may be eliminated through the sweat glands as well, although clearance by this route is minimal.⁹