Mercury works its way into the food chain, with women and children most at risk from poisoning, which can cause brain and nerve damage resulting in impaired coordination, blurred vision, tremors, irritability and memory loss.

"Mercury levels have to be reduced and we want governments to start to take steps to do this immediately," UNEP Executive Director Klaus Toepfer told reporters at a conference of environment ministers in the Kenyan capital Nairobi.

"Things could get worse in the coming years, as increases in temperature also appear to help the spread of the mercury."

UNEP's first report into the global impact of mercury pollution said more than 1,500 tonnes of the hazardous substance is pumped into the skies every year by power stations, with Asia and then Africa the worst culprits.

Small-scale mining, where mercury is used to help extract gold and silver from ores, is another main source of the pollution, releasing about 400-500 tonnes of mercury each year.

UNEP said a U.S. study found about one in 12 women there had mercury levels in their bodies above those deemed safe by national authorities.

Scientists predict that as a result, up to 300,000 babies in the United States could be at risk of brain damage with possible impacts from learning difficulties to impaired nervous systems.

Mercury poisoning also threatens animals such as otters, minx, osprey, eagles and some whales which feed on fish, which scientists say are readily contaminated by mercury pollution.