Delegates from 140 countries and territories yesterday signed a United Nations treaty to control mercury near the site of Japan's worst industrial poisoning, after Tokyo pledged US$2 billion to help poorer nations combat pollution.
The delegates gathered in Minamata city to sign the world's first legally binding treaty on the highly toxic metal.
The Minamata Convention on Mercury is named after the Japanese city where tens of thousands of people were poisoned - about 2,000 of whom have since died - by eating fish and shellfish taken from waters polluted by discharge from a factory.
The treaty will take effect once ratified by 50 countries, which the United Nations Environment Programme expects will take three to four years.
"This is the first step the human race has taken to reduce the threat posed by mercury," Japanese Environment Minister Nobuteru Ishihara, the conference chairman, said.
"We will work hard so that many countries ratify the treaty soon."
Minamata is a byword in Japan for sluggish official responses and the development-at-all-costs attitude that characterised decades of booming growth after the second world war.
The poisoning was brought to light in the mid-1950s by a doctor whose patients had damaged immune systems or who had developed brain or nervous system problems. Industrial pollution was suggested as a possible cause.
But it was not until 1968 that the factory stopped pumping out its mercury-laden waste.
In a video message to the opening ceremony on Wednesday, Japanese Prime Minister Shinzo Abe pledged US$2 billion to help developing nations address environmental pollution between 2014 and 2016.
"Precisely because we experienced and overcame damage from mercury, Japan bears responsibility for spearheading the world's efforts to eliminate it," Abe said.
But the comments provoked anger in Minamata, where many are still suffering the effects of decades of toxic dumping.
"The government, which bears responsibility, should not declare it has 'overcome' the issue. We are still on the way to overcoming Minamata disease," sufferer Masami Ogata, 55, said.
The treaty sets a phase-out date of 2020 for a list of products - including mercury thermometers - and gives governments 15 years to end all mercury mining.
But environmental groups say it stops short of addressing the use of mercury in artisanal and small-scale gold mining, which threatens the health of miners including child labourers in developing countries.