* Mercury is used to separate gold from ore, spreads worldwide
* 120 nations to meet in Geneva to work out anti-mercury treaty
* Mercury can cause brain damage in children
By Environment Correspondent Alister Doyle
OSLO, Jan 10 (Reuters) - High gold prices are driving up the use of toxic mercury in small-scale mining in developing nations, spreading a poison that can cause brain damage in children thousands of miles away, a U.N. study showed on Thursday.
Negotiators from 120 nations will meet in Geneva next week for a final round of talks meant to agree a treaty to reduce the use of mercury. It is mainly emitted by gold mining, where it helps separate gold from ore, and by coal-fired power plants.
A leap in gold prices to almost $1,700 an ounce from $400 less than a decade ago has spurred a surge in small-scale gold mining in South America, Africa and Asia which employs up to 15 million people, the U.N. Environment Programme (UNEP) said.
Workers risk acute poisoning and, released to the air or washed into rivers and the oceans, mercury emissions spread worldwide.
Mercury, a liquid metal also known as quicksilver, can cause harm especially to the brains of foetuses and infants.
"Exposing infants and mothers to mercury is a cruel and increasingly unnecessary risk," Achim Steiner, head of UNEP, told Reuters by telephone from Nairobi, adding that there were cleaner alternatives to mercury in mining.
"A Chinese baby born today, just like an American or a Japanese or a Brazilian one, really shouldn't be condemned to have neurological damage as a result of mercury," Steiner said.
"The very high gold price has ... brought more people, especially at the poorest end of society, into the gold mining sector," Steiner said. UNEP said damage to health and the environment was increasing as a result.
Emissions of mercury from artisanal and small-scale gold mines more than doubled to 727 tonnes in 2010 from 2005 levels and now made up 35 percent of the global total, UNEP said.
Part of the surge reflected better data - some mines in operation for years had been unknown, such as in West Africa.
Eating fish is the main way mercury builds up in humans. It enters rivers and the oceans and accumulates as methylmercury in the bodies of fish, especially big predators such as swordfish, shark, king mackerel, tuna and sea bass.
The report estimated that human emissions of mercury totalled almost 2,000 tonnes in 2010, mostly from Asian nations led by China. It said that level had been roughly stable for the past 20 years despite efforts for deeper cuts after a peak in the 1970s.
Mercury also comes from natural sources such as volcanoes.
The U.N. plan is to hold an international conference in late 2013 in Minamata, Japan, the site of one of the worst industrial releases in the 1950s, to approve a new convention to restrict mercury based on texts to be agreed in Geneva.
Steiner expressed hopes that a U.N. convention would spur innovation by companies to cut mercury use. Technologies include filters for coal-fired power plants or substitutes in products such as thermometers, lightbulbs and dental fillings.
Many nations have tightened laws - the United States barred exports of mercury from Jan. 1, 2013. The European Union, until 2008 the main global exporter, barred exports in 2011.
UNEP's study did not provide an estimate for the overall health and environmental damage caused by mercury.
UNEP spokesman Nick Nuttall said that limiting dangerous metals such as mercury could have huge benefits.
He noted that one study in 2011 put the benefits from phasing out another poison - lead in gasoline - at more than $2 trillion a year by reducing pollution linked to heart disease, diminished intelligence and even high crime rates.
($1 = 0.7667 euros) (Reporting by Alister Doyle; editing by Jason Neely)