Switzerland, Norway and Japan each contributed $1 million to get the treaty started, but U.N. officials say tens of millions more will be needed each year to help developing countries comply. The money would be distributed through the Global Environment Facility, an international funding mechanism.

The U.N. Environment Program said the treaty will be signed later this year in the southern Japanese city of Minamata, for which it is to be named. After that, 50 nations must ratify it before it comes into force, which officials predicted would happen in three to four years.

So-called Minimata disease, a severe neurological disorder caused by mercury poisoning, was discovered in the late 1950s because of methylmercury escaping from the city's industrial wastewater. The illness, which sickened people who ate contaminated fish, killed hundreds and left many more badly crippled. Some 12,000 people have demanded compensation from Japan's government.

"To agree on global targets is not easy to do," Achim Steiner, the executive director of the U.N. Environment Program, told reporters. "There was no delegation here that wished to leave Geneva without drafting a treaty."

Over the past 100 years, mercury found in the top 100 meters (yards) of the world's oceans has doubled, and concentrations in waters deeper than that have gone up by 25 percent, the U.N. environment agency says, while rivers and lakes contain an estimated 260 metric tons of mercury that was previously held in soils.

The treaty was originally blocked by powers such as the United States, but President Barack Obama's reversal of the U.S. position in early 2009 helped propel momentum for its adoption. China and India also played key roles in ensuring its passage; Asia accounts for just under half of all global releases of mercury.

"We have closed a chapter on a journey that has taken four years of often intense, but ultimately successful, negotiations and opened a new chapter toward a sustainable future," said Fernando Lugris, the Uruguayan diplomat who chaired the negotiations.

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