In general, radioactive substances are dangerous to humans because of the powerful energy they emit which creates free radicals - molecules with an odd number of unpaired electrons. These molecules react with surrounding compounds to gain electrons that will make them stable, and in doing this, cause damage to cells.  We are exposed to free radicals everyday in the environment, for example from pollution and cigarette smoke, and typically antioxidants in the body are able to neutralise some of their effects.  Usually, the impact of free radicals accumulates with age.  But radiation produces many free radicals so quickly that their effects are hard to counteract and they react to form toxic compounds that kill surrounding cells.

Alpha rays can be stopped by a sheet of tissue paper, beta rays by aluminum and gamma rays by lead.

Contrary to radioactive elements that can harm the body simply by exposure, polonium is only harmful if it’s ingested, inhaled, or absorbed through an open wound.  This is because polonium emits alpha particles which cannot penetrate through skin.  Alpha radiation can be stopped with a sheet of tissue paper, whereas exposure to substances that emit beta or gamma rays are much more risky since they require aluminium and lead (respectively) to stop the radiation.

But once polonium enters the body, its effects are devastating.  Litvinenko lost his hair shortly after the substance was in his body, he suffered from gastrointestinal problems, and his bone marrow failed – the body’s location for producing blood and immune cells.  Most of his organs were probably affected too since polonium is known to spread to all the body’s tissues whereas other radioactive elements bind to specific tissues and have a more localised effect.

After Litvinenko’s tragic death, investigators were focussing on making sure that no one else had been exposed to the substance.  Very small amounts of polonium were found in many locations in London where he had been on November 1st, but so far no one else is thought to have been affected.  Detectives are now trying to solve the whole mystery – including where the polonium could have originated from, and how and where the former spy was poisoned.  By following its traces, which is now taking the investigation aboard planes, the case will hopefully have a satisfying ending.