Global emissions of mercury from man-made sources fell 30 percent from 1990 to 2010, in part from decreasing use of coal, the U.S. Geological Survey reported Wednesday.

The greatest decline of the toxic pollutant was in Europe and North America, offsetting increases in Asia, the agency said, citing an international study. The findings challenge long-standing assumptions on emission trends and show that local and regional efforts can have a major impact, it said.

"This is great news for focused efforts on reducing exposure of fish, wildlife and humans to toxic mercury," said David Krabbenhoft, a USGS scientist and one of the study's co-authors.

A metal that poses health risks, mercury can be converted into a gas during industrial activities as well as such natural events as volcanic eruptions.

The study was carried out by the USGS, Harvard University, China's Peking University, Germany's Max Planck Institute for Chemistry and the University of Alberta in Canada. It was published in the Proceedings of the National Academy of Sciences.

The analysis found that the drop came because mercury had been phased out of many commercial products. Controls have been put in place on coal-fired power plants that removed mercury from the coal being burned.

Many power plants also have switched to natural gas from coal, the USGS said.