Most of mercury deposited in U.S. originates outside the country, EPRI report concludes

Palo Alto, Calif., Jan. 2, 2004 — Recent research has shown that mercury depositing on the earth’s surface within the U.S. predominantly originates outside the country, and, according to researchers at the Electric Power Research Institute (EPRI), some of it is from natural sources such as volcanoes and hot springs.

The movement of mercury is tracked in two ways: by direct measurements from aircraft flying through air plumes, and by modeling, in which computer programs simulate the movement of mercury in wind currents and its interactions with rainfall.

Leonard Levin, technical leader in air toxics at EPRI says, “Direct measurements have revealed significant levels of mercury exiting mainland Asia and crossing the Pacific to the U.S. In 2001 and 2002, EPRI, in cooperation with the National Center for Atmospheric Research, NASA, NOAA, and other agencies, used aircraft to measure mercury in air plumes exiting China near the city of Shanghai, following them over the Pacific for 400 miles. A later set of flights over the Pacific between southern California and Oregon found evidence of the same plume crossing the California coast.”

Studies being published in the technical journal Environmental Science and Technology by Seigneur et al. and based on computer model simulations also show most of the mercury deposited within the U.S. coming from globally distant sources.

These results indicate that most of the mercury appears to originate in Asia, which releases roughly half of the global human-origin mercury emitted, and is carried eastward across the Pacific by prevailing global wind patterns.

In the U.S., two-thirds or more of the mercury deposition west of the Mississippi is of non-U.S. origin. East of the Mississippi, where there are more sources of mercury than in the west, deposition is increasingly from U.S. sources, including, but not exclusively, from coal-fired power plants.

Recently released EPA computer-simulation study results show that several Midwestern states get from one-fifth to one-half of their mercury from non-U.S. sources.

The computer models used have been tested against actual mercury deposition data, and accurately reproduce the many measurements of mercury deposited around the U.S. obtained at the national Mercury Deposition Network monitoring stations.

Recently published work performed in Florida by a number of researchers has also found evidence that most of the mercury entering south Florida originates in other countries and is carried west into Florida by the dominant trade winds there.

Another Florida study found that, after mercury sources in the state (mostly municipal and medical waste incinerators) were controlled, thus reducing mercury emissions, the levels of mercury in Everglades fish did not show a clear pattern of response.

Some fish in some locations did show a mercury decline, while mercury levels in other fish populations remained unchanged and several, in fact, exhibited increasing levels of mercury.

“These studies point to the possibility that, due to the dominance of non-U.S. sources, for much of the United States, even relatively strong steps to control mercury from U.S. coal-fired utility boilers could prove somewhat disappointing. For that reason, continuing research is needed,” says Levin.

For well over a decade EPRI has been conducting research on all aspects of mercury and the environment. This includes research on mercury sources, movement, chemical transformation in the environment, health effects, and methods of reducing mercury emissions from power plants.

For further information about mercury, see the EPRI backgrounder “Frequently Asked Questions about Mercury” at

EPRI, headquartered in Palo Alto, Calif., was established in 1973 as a non-profit center for public interest energy and environmental research. EPRI’s collaborative science and technology development program now spans nearly every area of power generation, delivery and use.

More than 1,000 energy organizations and public institutions in 40 countries draw on EPRI’s global network of technical and business expertise.


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