People in developing countries are facing increasing health and environmental risks linked to exposure to mercury, a U.N. report says.

Parts of Africa, Asia and South America are at risk of increasing emissions of mercury into the environment, mostly the use of the toxic element in small-scale gold mining and through the burning of coal for electricity generation, a release from the U.N. Environment Program said Thursday.

"Mercury, which exists in various forms, remains a major global, regional and national challenge in terms of threats to human health and the environment," UNEP's Executive Director Achim Steiner, said in a statement.

Mercury released from industry and other man-made sources can circulate in the environment for up to centuries at a time, the UNEP report said, requiring years or even decades before reductions in mercury emissions have a demonstrable effect on mercury levels in nature and in the food chain.

Emissions of the toxic metal from small-scale gold mining have doubled since 2005, the report authors said, and rising gold prices will almost certainly lead to further increases.

Annual emissions from small-scale gold mining are estimated at 727 tons, 35 per cent of the global total, they said.

Action by governments, industry and civil society are needed to strengthen efforts to reduce mercury emissions and, Steiner said.

"Mercury has been known as a toxin and a hazard for centuries -- but today we have many of the alternative technologies and processes needed to reduce the risks for tens of millions of people, including pregnant mothers and their babies," he said. "A good outcome can also assist in a more sustainable future for generations to come."