On the afternoon of 3 November 2006 Edwin Carter arrived at Barnet Hospital, London, in an ambulance. He was vomiting, had bloody diarrhoea, and was in a lot of pain. He had been like this for two days. His own doctor said it looked like typhoid, but it wasn’t typhoid. Staff at the hospital diagnosed gastroenteritis and started a course of antibiotics.

The man’s condition improved slightly, but there were puzzling discrepancies in his lab results. Someone suffering from a bacterial infection would be expected to have a high white blood cell count, as the body produces more of these cells to fight off the infection. In this case the white blood cell count was very low and decreasing. Perhaps this was a reaction to the antibiotics. Perhaps not.



Four days later, when her husband was still not making the expected recovery, Mrs Carter suggested poisoning. This sounded fantastical, and staff tried to reassure the couple, but wrote down in the patient’s notes: “Patient and wife concerned about intentional infection of patient, query poison?”



Diagnosing any disease or medical condition that is out of the ordinary is a considerable challenge for doctors. In the case of poison, some substances leave characteristic traces; others mimic some symptoms of natural disease. Untangling everything can be time-consuming and frustrating for medical staff, and is of course worst for the patient.



A week later, Carter’s condition was still not improving. Then on 11 November, his hair started to fall out. This is a symptom most people associate with chemotherapy treatments for cancer. But, it is also a classic sign of thallium poisoning. Thallium is a heavy metal, which in the form of a salt is readily absorbed into the body where it can inflict considerable damage, and if more than about one gram is ingested, can prove fatal.



Thallium poisonings are rare, but in the 1970s Graham Young used thallium salts to poison several of his work colleagues; two died. The police investigation and forensic test that were developed as a result of this case meant that toxicologists and medical staff had protocols for detecting and treating thallium poisoning. While doctors awaited test results, Carter was treated with the thallium antidote, Prussian blue.



While Carter showed some classic signs of thallium poisoning, other symptoms were worrying absent, such as painful pins and needles in the feet and hands, along with numbness. But thallium can present a wide range of symptoms, which is why it had taken the police some time to track down Graham Young in the 1970s.



Meanwhile, Carter’s platelets count was also worryingly low. In fact, he looked more and more like someone who was suffering from radiation sickness. A Geiger counter was brought in and run up and down Mr Carter’s body but registered nothing above the normal background levels.



Then the results from the thallium test came back. They were slightly, but not much, above normal environmental levels. The more tests that were carried out, and the more results that came back, the more confusing the picture became. Poison, a theory that remained unshakeable with Mr and Mrs Carter, started to look like a very real possibility. The police were brought in.



On 17 November, Carter was transferred to University College Hospital where he could receive more specialist care. The same day, two detectives arrived at his bedside and began questioning him. Almost nine hours of interviews were recorded over the following three days. Carter talked of meetings with Russian and Italian business partners and secret agents. It was all starting to sound like something out of a Bond film. Surely this was the stuff of fiction?



Except that sometimes fact can be more incredible than fiction. In 1978, London had been the location for a notorious assassination using poison. Georgi Markov, a Bulgarian dissident had a ricin-laced pellet fired into his thigh while he was standing on Waterloo Bridge. The assassination was alleged to have been carried out using a modified umbrella wielded by Bulgarian secret service agents with help from the KGB.



On 20 November 2006, just after his police interviews were concluded, Carter was moved to intensive care. His major organs were starting to fail. Still there was no diagnosis.



There were more tests. A litre of Carter’s urine was sent to medical staff at the Atomic Weapons Establishment for testing. On 23 November the results came back: polonium210 had been detected.



Six hours later, Carter went into cardiac arrest and despite the best efforts of medical staff, he could not be revived. Mr Edwin Carter, the name adopted by Alexander Litvinenko when he first arrived in the UK, was declared dead. Alexander Litvinenko became the first confirmed victim of deliberate poisoning by polonium210.



‘Edwin Carter’, whose real name was Alexander Litvinenko, in hospital shortly before his death from polonium poisoning. Photograph: Natasja Weitsz/Getty Images

No wonder medical staff struggled with a diagnosis when there were no known cases to refer to. Even when the poison was identified, it was such an obscure substance that few people in the world knew anything about it, let alone what it would do to a human body.



Polonium is a radioactive metal first discovered by Marie Curie in 1898 and named after her native Poland. It took Curie years to extract a minuscule amount of pure polonium from around two tonnes of pitchblende. It gained her a Nobel Prize (her second), but she was probably also the element’s first victim when she died in 1934 of aplastic anaemia – a direct result of her years working with radioactive materials.



Extracting polonium from pitchblende is an inefficient and dangerous way of doing things. Today it is produced in nuclear reactors, although the majority of these facilities do not isolate the polonium that is produced. The world’s supply of polonium (used in anti-static devices) comes from one nuclear plant in Russia. There are the two options available for anyone wanting to get hold of polonium: buy it on the black market (far from easy, illegal and very, very expensive), or make it yourself (difficult to achieve surreptitiously and very likely to kill you in the process).

Even if you can get your hands on a small piece of pure polonium this won’t be much good to you as a poison. The body doesn’t absorb metals very well, so you will need to turn it into a salt. The chemistry is easy (add a bit of acid) but the process is incredibly dangerous because of the radiation emitted. It would be suicidal to try it without specialist knowledge and suitable protective equipment.

Having got hold of polonium in a suitable form, Litvinenko’s killers added it to a pot of green tea at the Pine Bar in the Millennium Hotel, London. Litvinenko didn’t drink much of the tea, but he didn’t need to. The 26 micrograms that were found in his blood (a quantity so small you would struggle to see it without the help of magnifying glass) was more than enough to kill him.

Polonium’s poisonous potency is due to the high energy alpha particles it emits when the atoms decay. Alpha particles will rip apart the first thing they encounter, be it a molecule of water, fat, protein or DNA. An alpha particle will create incredible devastation in its path, but that path is very short – just a few millimetres within the body. It’s enough to destroy cells, and if enough cells die an organ will fail, but the particles can’t reach far enough to escape the body itself. This is why when radiation detectors were passed over Litvinenko’s body they couldn’t detect the cause of the destruction going on inside. Most alpha-emitters also give off powerful gamma rays, which are easily detected outside the body, but polonium210 rarely does. Perhaps this was known to those plotting Litvinenko’s death and they hoped the poison would therefore go undetected.

However, polonium outside of the body – for example, on the hands and clothes of those who handled the poison and anything they came into contact with – is much easier to detect. Using such an exotic poison, although possibly chosen because it was thought to be untraceable, in fact makes it easier to find. Finding traces of highly characteristic polonium radiation in any location is highly suspect.

But how do you develop a test for something previously unknown? This may have been the first case of murder with polonium, but polonium itself, and radiation science, have been known for over a century. The chemistry of metals has been known for even longer. It was some very basic chemistry that allowed scientists to extract polonium from Litvinenko’s urine sample. It involves boiling the sample with a series of acids so that in the final stage polonium will spontaneously deposit on the surface of a silver disc placed in the liquid. This disk can then be held in front of a radiation detector and the tell-tail signs of polonium’s alpha radiation can be measured. Once identified, old texts on the characteristics of polonium can be dusted off and used to develop protocols for detection.

Sadly, this knowledge offers little hope for treatment in cases of polonium poisoning. Once Litvinenko had swallowed his first mouthful of tainted tea, his fate was almost certain. There is simply no way of removing all the polonium from the body and repairing the damage done.

An intense and thorough investigation into the death of Alexander Litvinenko has produced damning evidence against his killers, though it seems unlikely they will ever stand trial. It has also raised speculations over other mysterious deaths in Russia and elsewhere. The death of Yasser Arafat in 2004 has been linked to polonium210, but there are also other theories over the cause.

The difficulty of getting hold of polonium210 means, luckily, it is beyond the means of most individuals. And, if nothing else, Litvinenko’s case has meant that there are now established protocols for the detection of polonium. But that’s fairly cold comfort in the light of such a tragic and brutal case.