By Alex Kirby BBC News Online environment correspondent in Nairobi

The threat to health from mercury emissions is far more widespread than previously supposed, the United Nations says.

It is urging governments to introduce drastic reductions

There are technologies available already which will reduce mercury emissions from power stations by about 80% James Willis, Unep

A United Nations Environment Programme (Unep) report says 70% of mercury emissions of human origin come from the burning of coal and the incineration of waste materials.

Yet the technology to eliminate most of them already exists.

The report, Global Mercury Assessment, will be discussed at the meeting here of Unep's governing council from 3 to 7 February.

Mercury is a naturally occurring metal released into the environment from rocks and soils, and in volcanic eruptions. But human activities, including mining, industry and power generation, are continually adding more.

Once released, mercury can travel long distances.

Contaminated seafood

Dr Klaus Toepfer, Unep's executive director, said at the report's launch: "Mercury is a huge problem, a traveller without a passport, that spreads around the world in air and water.

"Action is necessary. We have to reduce drastically and as soon as possible the risk it poses to a lot of people."

Dr Toepfer told BBC News Online: "With another global health threat that especially affects children, lead in petrol, I am absolutely convinced we can reach agreement by 2005 to phase it out worldwide.

"I believe the aim of drastically reducing mercury from man-made sources is a must, too."

One of the commonest ways mercury affects people is in one of its organic forms, methylmercury.

This was the cause of Minamata disease in Japan nearly 50 years ago, when more than 1,400 people died after eating contaminated seafood.

Methylmercury attacks the central nervous system; symptoms include numbness and unsteadiness, tiredness, ringing in the ears, and problems with vision, hearing and speech.

Canadian seals

It is a particular risk to pregnant women and their foetuses, infants, children, and people whose diet includes a lot of fish.

Emerging evidence also links mercury to cardiovascular, thyroid and digestive problems.

The Unep report says that while fish provide nutrients often not available in other foods, mercury is a major threat to consumers, especially in large predatory species like tuna, shark and barracuda.

A study of women in the US found almost five million had mercury levels above the level considered safe by the US Environmental Protection Agency.

In northern Greenland 16% of the people have levels above that which can be toxic to non-pregnant adults.

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 risen by between two and four times over the last 25 years in parts of Canada and Greenland.

There is recent evidence that mercury is damaging the soil over much of Europe and possibly elsewhere.

Stormy weather

The report says coal-fired power stations and waste incinerators produce about 1,500 tonnes of atmospheric mercury emissions a year, with a further 4-500 tonnes estimated to come from mining of gold and silver using basic, non-industrial methods.

It says higher temperatures, increased storminess and more extreme weather will increase releases of mercury from soils and sediments.

High levels of acidity in rivers and lakes also appear to trigger releases.

In Sweden, 50% of the lakes contain pike whose mercury limits exceed international health limits.

James Willis, head of Unep's chemicals division, told BBC News Online: "There are technologies available already, like wet scrubbers, which will reduce mercury emissions from power stations by about 80%.

"Getting down to zero is something else. But what we can do now is often cheap - and it can cut other pollutants as well."