Selenium poisoning? No! Marco Polo's travelogue misinterpreted 

    Mineral selenium did NOT kill or sicken the donkeys in Marco Polo's travelogue, Chinese scientists have found.

    "Generations of scientists thought Marco Polo was the first to write about selenium poisoning. They were wrong," said Shao Shuxun,a geochemist with the Chinese Academy of Sciences.

    The Italian explorer came to China in 1271 via the ancient Silk Road. In his travelogue in 1295, he said a toxic wild plant in today's Gansu Province killed many cattle.

    Many donkeys, oxen and horses, which were an important means of transportation in China in those days, suffered hair loss and festers on their hooves and some of them even died, he wrote.

    In the early 1900s, some cattle on a U.S. farm had the same symptoms after eating clovers, whins or vetches. A U.S. scientist found after lab analysis that toxic levels of the mineral selenium were the killer.

    Worldwide scientists then associated these poisoning cases with the donkeys in Marco Polo's book, and held "Marco Polo's Travels" was the world's earliest record of selenium poisoning.

    Shao and his research team meticulously read through Marco Polo's original work and historical documents about China's geography before they were able to locate the places of the poisoning. They then followed the Italian traveler's route and collected samples of water, rock, soil and herbs.

    "We found through lab work that the selenium levels in these samples were perfectly safe," said Shao. "Actually, the selenium level in the entire region is so low that high-selenium plants are unlikely to grow in such an environment."

    The selenium levels in local plants are far lower than the safety standards set by the World Health Organization, says Zheng Baoshan, a researcher with a CAS laboratory for environment and geochemistry and a member of the research team. "We're certain what Marco Polo described was not selenium poisoning."

    A substance known as "swainsonine", which abounds in many plants on pastures of Gansu Province, was more likely the killer, the research team suggested.

    Tianzhu and Sunan counties, which are located at the heart of Marco Polo's route in western China, have 130,000 hectares of these toxic plants. "Each year, these plants poison about 20,000 heads of cattle, killing 22 percent of them and causing miscarriages in another 29 percent," said Shao.

    The research finding will hopefully correct scientists' misinterpretation of Marco Polo's work, said Olle Selinus, a Swedish scientist and president of an international medical geology society.

    Selenium is not typically harmful to humans, but can be poisonous if combined with other compounds or consumed at high levels.

    Marco Polo came to China when he was 17 and his travelogue is known as the first book about China by a Westerner.