THE terracotta warriors that have stood guard around the tomb of China’s first emperor for more than 2,000 years may be facing their toughest battle yet: how to survive the depredations of age and air.

A Chinese scientist said this week that the 8,000-strong army is in danger of crumbling into dust, a prediction that has prompted a flurry of denials from government officials.

Cao Junji, of the Institute of Earth Environment at the Chinese Academy of Sciences, suggested that the soldiers could disintegrate as the oxidisation that has transformed the colourfully painted figures into grey statues eats deeper into the surface of the clay.

“If nothing is done now, in 100 years the warriors may have corroded to such an extent that the pits will look just like a coalmine and not have any aesthetic value,” Mr Cao said. “If a leg or shoulder falls off, the whole figure is damaged.”

The faces of the warriors, each moulded and painted as individuals with unique features, could gradually lose their moustaches and hairstyles, Mr Cao said. That would greatly diminish their cultural value.

He said that temperature, humidity, pollutants and sunlight all threatened the figures. “It’s very hard to restore the original colour of the statues that have already been exposed to the air, but as the museum is still excavating new ones, we need to conduct more research to avoid a repeat of old problems.”

A two-year research project, focusing on air pollution, is under way to assess the extent of damage to the life-size clay figures excavated from the plains outside the ancient northern city of Xian. But officials said that the project was intended for prevention rather than cure, and that Mr Cao had been irresponsible to suggest that the figures could crumble.

Wu Yongqi, director of the Museum of Qin Terracotta Warriors and Horses, said: “We are carrying out the research project for precautionary protection, not for measures to deal with existing problems.

“The terracotta warriors and horses are perfectly safe and so they will remain in 100 years. Any scaremongering about the relics without any scientific foundation is ill-intentioned.”

The warriors attract more than 1.5 million tourists a year and have achieved a fame to compete with the Great Wall since they were discovered by farmers in 1974.

More than 8,000 clay soldiers and 500 horses have been found in three burial pits positioned to protect the tomb of Qin Shih Huang Di, who ruled from 221BC to 210BC.

The first emperor of a unified China is famed as much for his creation of a vast network of roads and canals and for standardising weights, measures and writing as for his despotic decision to bury alive hundreds of scholars and burn all non-technical books.

He was obsessed with his mortality, putting 700,000 prisoners of war and slaves to work for 36 years to build a tomb that he spent the last years of his life striving to avoid, employing magicians and alchemists to discover the elixir of life. He died at the age of 49.

His tomb, according to legend, is one of the most elaborate buildings of ancient times, equipped with rivers of mercury and booby-trapped against robbers. The contents remain a mystery and the tomb is still a mountain of grass-covered earth because officials have said that it will not be excavated for 100 years.

Archaeologists already have enough work to do to preserve the emperor’s bodyguards. There are two main problems — protecting the colours painted on the soldiers and strengthening the walls of the huge pits that contain them.

A way of protecting the colours was found in 1998, after 20 years of research, when a breakthrough enabled archaeologists to paint the soldiers with a solution containing polyurethane and other chemicals. The figures are further protected by a hangar-like structure. Flash photography is forbidden, and all vehicles must park far from the museum to prevent vibrations that could disturb the site.

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