LONDON: Arsenic, the classic poison slipped into the food and drink of emperors, politicians, popes and unsuspecting heiresses down the ages, is shaking off its disreputable history.

Arsenic's notoriety ensures that its mere mention still sends a shiver down many spines - despite earlier successes in treating major diseases such as syphilis and tuberculosis.

But many scientists and doctors are now starting to recognize arsenic's positive qualities.

Recent research suggests that small amounts of arsenic may actually benefit human health.

The infamous substance is already used to treat certain kinds of blood cancer.

Arsenic, a brittle steel-grey element, is not very poisonous in its natural state.

But the adverse properties of its compounds, or arsenicals, have been known for more than 2,000 years and made it a virtual synonym for poisoning and sudden death.

One of these compounds, white-coloured arsenic oxide, is extremely toxic and was for many centuries the murderer's poison of choice because it was notoriously difficult to detect in corpses. Scientists only developed a reliable test in the 19th century.

Unfortunately, this test came after the death in 1821 of France's former emperor Napoleon Bonaparte, now believed by some scientists to have been slowly poisoned by fumes exuding from his decaying wallpaper, which was dyed with a green pigment containing arsenic. Stomach cancer was the official verdict at the time.

After baffling authorities for years, it was discovered that if wallpaper containing these pigments became damp, the animal glues commonly employed in those days would form a mould that would convert the pigment into toxic arsenic vapour.

Along with cyanide and strychnine, white arsenic won such a terrible reputation that in France it was dubbed"inheritance powder" because so many people used the tasteless and odourless substance to murder rich relatives so they would inherit sooner.

Arsenic can kill quickly if consumed in large quantities, though small amounts of exposure over a long term can lead to a much slower death.

In earlier centuries, symptoms of arsenic poisoning were easily confused with those of many other illnesses.

Despite its reputation as a first-rate poison, arsenic does have a better side and scientists have recently discovered several beneficial uses.

Arsenic's role in the treatment of disease is long and varied. Doctors have used arsenicals at various stages in history to treat sleeping woes, tuberculosis and skin diseases, among other illnesses.

"People are frightened to death of arsenic," said Samuel Waxman, a clinical professor and cancer specialist at the Mount Sinai School of Medicine in New York. "They're frightened that it's poison, that it's a cancer-producing agent but... that drug was used in one form or another going back to Hippocrates. Its use peaked around the late 1800s, and early 1900s, and it was one of the two or three drugs carried around by every physician for almost anything."

Peasants in 19th-century Styria, now southern Austria and northern Slovenia, used to quite happily ingest large amounts of arsenic to boost their strength and sexual potency.

One arsenical discovered in 1909, arsphenamine, was the main treatment for syphilis until it was replaced by penicillin in the 1940s. And the compounds were used so widely in embalming in 17th-century Britain that arsenic leaching from old cemeteries is a known groundwater pollutant even today.

While arsenic's use in contemporary medicine has been severely curtailed, it still plays a role in treating severe parasitic diseases.

Outside medicine, it is a key component of semiconductor devices, mainly in the form of gallium arsenide.

In the last few years, arsenic has won praise from the medical community after its trioxide, used for centuries by traditional Chinese herbalists to fight disease, was shown to have beneficial effects on certain cancers - particularly acute promyelocytic leukaemia (APL).

People suffering from this blood disorder have a mutated gene that creates a malformed protein in their bodies and interferes with the normal growth and death of certain white blood cells.

Arsenic trioxide, marketed as Trisenox and approved by the US Food and Drug Administration (FDA), makes the protein destroy itself and allows white blood cells to grow normally.

"It's absolutely conclusive that this drug is the most predictable form of treatment for this kind of leukaemia," Waxman said.

Trisenox, which some doctors say is less toxic than conventional chemotherapy, shows promise in treatments of other kinds of cancer and is undergoing clinical trials for lymphoma, prostate and cervical cancers.

In addition, recent research shows that too little arsenic present in the body may be detrimental to the health of humans and animals while tiny amounts may actually be of nutritional importance.

Arsenic has been shown to have a beneficial effect when fed to some laboratory animals.

Agencies via Xinhua

　　From Chinadaily.com.cn