Image caption Rising gold prices has seen an increase in small-scale gold mines, most of which use mercury

More than 140 countries have agreed on a set of legally binding measures to curb mercury pollution, at UN talks.

Delegates in Geneva approved measures to control the use of the highly toxic metal in order to reduce the amount of mercury released into the environment.

Mercury can produce a range of adverse human health effects, including permanent damage to the nervous system.

The UN recently published data that showed mercury emissions were rising in a number of developing nations.

The deal was agreed after all-night talks.

"After complex and often all night sessions here in Geneva, nations have today laid the foundations for a global response to a pollutant whose notoriety has been recognised for well over a century," UN Environment Programme executive director Achim Steiner said on Saturday.

"Everyone in the world stands to benefit... in particular the workers and families of small-scale gold miners, the peoples of the Arctic and this generation of mothers and babies and the generations to come."

The rules, known as the Minamata Convention and named after the Japanese town that experienced one of the world's worst cases of mercury poisoning, will open for nations to sign at a diplomatic conference later this year.

The convention will regulate a range of areas, including:

the supply of and trade in mercury;

the use of mercury in products and industrial processes;

the measures to be taken to reduce emissions from artisanal and small-scale gold mining;

the measures to be taken to reduce emissions from power plants and metals production facilities.

Ahead of the five-day meeting, Unep published a report warning that developing nations were facing growing health and environmental risks from increased exposure to mercury.

It said a growth in small-scale mining and coal burning were the main reasons for the rise in emissions.

As a result of rapid industrialisation, South-East Asia was the largest regional emitter and accounted for almost half of the element's annual global emissions.

Lasting effects

Mercury - a heavy, silvery white metal - is a liquid at room temperature and can evaporate easily. Within the environment, it is found in cinnabar deposits. It is also found in natural forms in a range of other rocks, including limestone and coal.

Image caption Burning coal is another major source of mercury emissions, the report says

Mercury can be released into the environment through a number of industrial processes including mining, metal and cement production, and the burning of fossil fuels.

Once emitted, it persists in the environment for a long time - circulating through air, water, soil and living organisms - and can be dispersed over vast distances.

The World Health Organization (WHO) says: "Mercury is highly toxic to human health, posing a particular threat to the development of the (unborn) child and early in life.

"The inhalation of mercury vapour can produce harmful effects on the nervous, digestive and immune systems, lungs and kidneys, and may be fatal.

"The inorganic salts of mercury are corrosive to the skin, eyes and gastrointestinal tract, and may induce kidney toxicity if ingested."

The Unep assessment said the concentration of mercury in the top 100m of the world's oceans had doubled over the past century, and estimated that 260 tonnes of the toxic metal had made their way from soil into rivers and lakes.

Another characteristic, it added, was that mercury became more concentrated as it moved up the food chain, reaching its highest levels in predator fish that could be consumed by humans.

Campaign group Zero Mercury Working Group co-coordinator Michael Bender called the global deal a "major accomplishment", but added: "Yet the instrument is hampered by weak controls on mercury emissions from major sources like coal-fired power plants."

He said new facilities would not be required to have mercury pollution controls for five years after the treaty came into force, with existing facilities given a decade before they had to begin their control efforts.

The World Coal Association (WCA), a trade body for the industry, said that burning coal account for about 24% of global mercury emissions and the use of "adequate technologies" could reduce emissions of the metal from coal-fired power stations by up to 90%.

WCA chief executive Milton Catelin said: "[The Convention] will ensure that countries are able to address the issue of mercury emissions from their coal-fired power plants via the application of technologies which are most appropriate in a given national context and for a given facility and without having to restrict the use of coal as an energy fuel or to compromise their economic development goals."