Following the poisoning of former Russian spy Alexander Litvinenko, British authorities are following a trail of radioactive contamination. Litvinenko died from the effects of absorbing a rare radioactive element, Polonium 210.
Polonium is a naturally occurring element. There are trace quantities in the soil, minuscule amounts in seafood and in consumer products, such as anti-static brushes found in photo shops.
Although it is described as one of the "nastier radioactive isotopes," Polonium is harmless unless it gets inside your body, through ingestion or a puncture wound, for example.