Study tracks big drop in global mercury emissions

Mercury from the Craig Station power plant in northwest Colorado pollutes lakes in Rocky Mountain National Park.
Mercury from the Craig Station power plant in northwest Colorado pollutes lakes in Rocky Mountain National Park. @bberwyn photo.

Local, regional controls help improve global picture

Staff Report

Global mercury emissions dropped by nearly a third between 1990 and 2010, according to a new study that tried to identify patterns and trends in mercury pollution.

Rapid economic development in Asia means higher mercury emissions, but reductions in North America were enough to offset the increases, according to scientists from China, Germany, Canada and the U.S.

Mercury is a metallic element that poses environmental health risks to both wildlife and humans when converted to methylmercury in ecosystems.  It can be converted into gaseous emissions during various industrial activities, as well as natural processes like volcanic eruptions.

Many ocean and freshwater fish are so tainted by mercury that governments have issued public health warnings on consumption. Recent studies have tracked mercury levels in seemingly pristine wilderness areas like the Grand Canyon, where scientists recently measured concentrations that exceed risk thresholds for wildlife. Mercury has also been detected in California’s coastal fogs.

In a national assessment, the U.S. Geological Survey found unhealthy mercury levels in 25 percent of all U.S. Streams. And near Hawaii, scientists say mercury concentrations in yellowfin tuna have been increasing 3.8 percent a year. Researchers have even documented signs of environmental stress in Alaskan sled dogs who primarily eat mercury tainted fish.

Plans by the EPA to further curb mercury emissions from power plants in the U.S. were foiled by the U.S. Supreme Court last year, when the justices ruled that the agency should have considered the economic cost of the proposed regulations at the start of the rule-making process.

“For years, mercury researchers have been unable to explain the apparent conundrum between declining air concentrations and rising emission estimates,” said lead author Yanxu Zhang from Harvard University. “Our work is the first detailed, mechanistic analysis to explain the declining atmospheric mercury trend.”

The observed reduction in atmospheric mercury was most pronounced over North America and Europe, where several factors have contributed to the observed declines in atmospheric mercury concentrations:

  • Mercury has been gradually phased out of many commercial products.
  • Controls were put in place on coal-fired power plants that removed naturally occurring mercury from the coal being burned.
  • Many power plants have switched to natural gas and stopped burning coal entirely, further reducing mercury emissions.

Finally, at the same time, efforts to combat acid rain resulted in controls being put in place on power plants to reduce nitrous oxide and sulfur dioxide emissions. This had the unintended benefit of also reducing mercury emissions.

“Previously, most mercury researchers subscribed to the notion that the ‘global mercury’ problem was largely manifested by a shared global emission inventory,” said USGS scientist David Krabbenhoft, one of the study’s co-authors. “However, our research shows that local and regional efforts to reduce mercury emissions matter significantly. This is great news for focused efforts on reducing exposure of fish, wildlife and humans to toxic mercury.”

“This is important for policy and decision-makers, as well as natural resource managers, because, as our results show, their actions can have tangible effects on mercury emissions, even at the local level,” said study co-author Vincent St. Louis with the University of Alberta.

The study is entitled “Observed decrease in atmospheric mercury explained by global decline in anthropogenic emissions,” and is published in the Proceedings of the National Academy of Sciences. Read more information about the study.

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