An article in Nigeria’s Saturday Sun has some background on thallium, the rare toxic metal that was evidently used to poison Mr Litvinenko:
Another political refugee was Nikolai Khokhlov who was haunted by the Russian government for listening to his conscience not to eliminate an innocent man. Though he had no unusual encounter with any person, Khokhlov, while participating in a convention at Frankfurt, Germany, became ill and later collapsed. Regaining consciousness, he suffered violent nausea that doctors treated as acute gastritis. But the treatment was unavailing. On Khokhlov’s fifth morning in a Frankfurt’s hospital, a nurse entered his room and stared at him in transfixed horror. “What is it?” Khokhlov demanded. Then he looked in a mirror with a horror of his own.
Hideous brown stripes, dark splotches and black and blue swellings disfigured his face and body. A sticky secretion oozed from his eyelids, and blood seeped through his pores; his skin felt dry, shrunken and aflame. At the mere touch of his hand, a shock of his hair fell out. An eminent professor of medicine suspected that he had been poisoned with thallium, a rare toxic metal. However, treatment with thallium antidotes had no effect. Tests showed that Khokhlov’s white corpuscles were being swiftly and fatally destroyed, his bones decaying, his blood turning to plasma, and his saliva glands drying up. That night doctors said his case was hopeless and death imminent.
Following pleas from the man whose life he had saved, Khokhlov was transferred to a US military hospital in Frankfurt. Protected constantly by armed guards, a team of six American physicians now began a duel with some unknown death specialists. Around the clock, they gave him massive injections of cortisone, vitamins, steroids, ACTH, and experimental medications, while keeping him alive with intravenous feeding and almost continous blood transfusions.
An anesthesiologist stood by, preparing solutions for Khokhlov’s mouth which was devoid of saliva, and otherwise trying to ease his agony. More specialists arrived for consultation and analysis and still newer drugs were rushed to Frankfurt. For a week, the supreme resources of American medicine barely kept Khokhlov alive.
Subsequently, a famous American toxicologist, who studied the medical records in consultation with colleagues, found the answer. Khokhlov was poisoned with thallium that had been subjected to intense atomic radiation, which causes the metal to disintegrate into tiny particles. Introduced into his body through food or drink, the radioactive particle disintegrated completely and permeated his system with deadly radiation.