World governments have agreed to crack down on mercury pollution.
Environment ministers meeting in Nairobi have initiated a process that should end in a legally binding, international treaty.
The landmark decision was taken by more than 140 countries attending the governing council of the United Nations Environment Programme (Unep).
Mercury compounds can be damaging to the central nervous systems of humans and animals.
Unep's Executive Director, Achim Steiner, said: "Unep has, for some seven years, co-ordinated and contributed to an intense scientific and policy debate on how best to deal with the issue of mercury.
"Today the world's environment ministers, armed with the full facts and full choices, decided the time for talking was over - the time for action on this pollution is now."
The key factor enabling ministers to agree a way forward has been the willingness of the new US Obama administration to buy into a treaty.
In his address to the council on Monday, US delegate Daniel Reifsnyder, said mercury was the "most important global chemical issue facing us today", and required "immediate action".
He said that a half of all mercury deposition within the US now came from sources outside its borders, and that only international coordination could address the problem.
The previous Bush administration had steadfastly opposed legally binding measures to control mercury.
The ministers meeting in the Kenyan capital agreed an eight-point interim plan to help curb pollution while awaiting the full treaty. This included:
• Boosting the world-wide capability for nations to safely store stockpiled mercury
• Reducing the supply of mercury from, for example, primary mining of the heavy metal
• Carrying out awareness raising of the risks alongside projects to cut the use of mercury in artisanal mining where an estimated 10 million miners and their families are exposed
• Reducing mercury in products such as thermometers and high-intensity discharge lamps, and in processes such as some kinds of paper-making and plastics production
Mercury is a naturally occurring metal released into the environment from rocks and soils, and in volcanic eruptions. But human activities are continually adding more.
The vast majority of human emissions come from the burning of coal and the incineration of waste materials. And of particular concern down the years has been the use of mercury to mine gold.
Poor gold mine practices have elevated levels of mercury in the environment
Gold particles will stick to mercury when the precious metal is panned. The resulting amalgam can then be burnt to recover the gold.
The practice followed in some developing nations has resulted in huge quantities of the heavy metal being washed into the environment, putting mine workers at risk.
One of the most common ways mercury affects people is in the organic form methylmercury.
Methylmercury attacks the central nervous system: symptoms include numbness and unsteadiness, tiredness, ringing in the ears, and problems with vision, hearing and speech.
It is a particular risk to pregnant women and their foetuses, infants, children, and people whose diet includes a lot of fish.
Animals and birds that prey on fish are also at risk, especially otters, mink, eagles and ospreys.
Mercury levels in Arctic ringed seals and beluga whales have also risen sharply in parts of Canada and Greenland.