By Tom Miles
GENEVA, Jan 17 (Reuters) - Agreement may be near on a global treaty to reduce the use of toxic mercury, but arguments about a few tens of millions of dollars are taking the talks to the brink, a U.N. official involved in the Geneva negotiations said on Thursday.
Another official predicted that the talks were likely to bring a deal late on Friday or in the early hours of Saturday, but it was still unclear whether the eventual text would be "a Swiss cheese" - full of holes.
The agreement as it stands would commit countries to phasing out mercury thermometers, some kinds of lightbulbs and small "button" batteries, with 2018 the earliest possible deadline, according to officials involved in the closed-door talks of 146 nations.
But other products, such as dental amalgam used as fillings for teeth, are likely to be excluded from the initial treaty coverage.
"The negotiations are now in their most critical and volatile phase," said the U.N. official, who spoke on condition of anonymity, calling the state of talks "a high-wire act".
"People have agreed a great deal and they're now homing in on the issues most difficult to address. Amongst them is finance and also the level of ambition in terms of what is in and what is out, or how long actions are deferred.
"There is still a possibility that three years of extremely intense negotiations, and countries looking for compromise solutions, could fall apart."
MILLIONS AGAINST BILLIONS
One participant said the developed countries were together being asked to contribute about $30-40 million per year to help with a problem that was likely to cost developing countries tens of billions.
"It's not aid that we're talking about here," said a third official involved in the talks, adding that the health of people all around the world was affected by mercury emissions.
Mercury is mainly emitted by gold mining, where it helps to separate gold from ore, and by coal-fired power plants.
As it is released to the air or washed into rivers and oceans, it spreads worldwide, and builds up in humans mostly through consumption of fish. The brains of foetuses and infants are particularly vulnerable to damage from mercury.
While China and India would have to install filters and scrubbers on their coal-fired power stations to prevent mercury in the coal reaching the atmosphere, Chile would have to stop the relatively large amount of mercury in its copper reserves leaking out when it mines the copper.
The treaty would also be likely to force a change in small-scale and artisanal gold mining, which doubled its mercury emissions between 2005 and 2010 as the gold price soared.
Mercury from such gold mines now makes up 35 percent of total global emissions, according to a study by the U.N. Environment Programme published last week.
The talks in Geneva are the fifth and final round of negotiations. If a deal is struck, the resulting convention is expected to be approved at a conference later this year in Minamata, Japan, the site of one of the world's worst industrial mercury releases in the 1950s.