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Researchers find high levels of mercury in California's coastal fog
Human-created mercury vapor rises to upper atmosphere, circles globe multiple times, lands on Earth, ends up in fish: UW study
December 18, 2011 by Stone Hearth News Newswise — Humans pump thousands of tons of vapor from the metallic element mercury into the atmosphere each year, and it can remain suspended for long periods before being changed into a form that is easily removed from the atmosphere.
New research shows that the upper troposphere and lower stratosphere work to transform elemental mercury into oxidized mercury, which can easily be deposited into aquatic ecosystems and ultimately enter the food chain.
“The upper atmosphere is acting as a chemical reactor to make the mercury more able to be deposited to ecosystems,” said Seth Lyman, who did the work as a research assistant professor in science and technology at the University of Washington Bothell.
Lyman, now with Utah State University’s Energy Dynamics Laboratory, is lead author of a paper documenting the research published online Dec. 19 by the journal Nature Geoscience. Daniel Jaffe, a science and technology professor at UW Bothell, is coauthor of the paper. The work was supported by a grant from the National Science Foundation.
The findings come from data gathered during research flights in October and November 2010 over North America and Europe by a National Center for Atmospheric Research aircraft.
The campaign used a device built at UW Bothell that can detect both elemental mercury and oxidized mercury in the same air sample, and the device recorded readings every 2.5 minutes. The flights typically are at altitudes of 19,000 to 23,000 feet, well below the confluence of the troposphere and the stratosphere, but several times during the 2010 flights – particularly on a trip from Bangor, Maine, to Broomfield, Colo. – the aircraft encountered streams of air that had descended from the stratosphere or from near it.
The result was the first time that the two mercury forms were measured together in a way that showed that elemental mercury is transformed into oxidized mercury, Lyman said, and evidence indicated the process occurs in the upper atmosphere.
Exactly how the oxidation takes place is not known with certainty but, once the transformation takes place, the oxidized mercury is quickly removed from the atmosphere, mostly through precipitation or air moving to the surface. After it settles to the surface, the oxidized mercury is transformed by bacteria into methyl mercury, a form that can be taken into the food chain and eventually can result in mercury-contaminated fish.
Some areas, such as the Southwest United States, appear to have specific climate conditions that allow them to receive more oxidized mercury from the upper atmosphere than other areas, Lyman noted.
He added that where the mercury settles to the surface can be thousands of miles from where it was emitted. For example, mercury from coal burning in Asia could rise into the atmosphere and circle the globe several times before it is oxidized, then could come to the surface anywhere. Understanding where it is oxidized and deposited would help efforts to predict ecosystem impacts of mercury emissions, he said.
“Much of emitted mercury is deposited far from its original sources,” Lyman said. “Mercury emitted on the other side of the globe could be deposited right at our back door, depending on where and how it is transported, chemically transformed and deposited.”
By Christopher Stolz, Special to the Star
December 10, 2011
A research team at UC Santa Cruz that this year for the first time tested coastal fog in California for mercury found raised levels of the element.
The team, led by chemist Peter Weiss-Penzias, reported finding "very high" levels of mercury, a neurotoxin, in the fog, according to a paper presented Thursday to a geophysical science conference in San Francisco on Thursday.
"These are unheard of levels for methylmercury," said Weiss-Penzias. "People have measured methylmercury downstream from old mercury mines, where the bugs [microbes] have to convert inorganic mercury in sediment into methylmercury, and the highest levels they found were four parts per trillion. Well, our highest levels were 10 parts per trillion."
Mercury is a naturally occurring element, but it can become toxic as it builds up in the environment, especially in fish, which can become hazardous to eat.
The toxin can cause a wide range of neurological problems, especially in young children, and is considered one of the most dangerous of all pollutants.
The fog is still safe to breathe, Weiss-Penzias stressed, but could be transporting the toxin from deep in the ocean to inland areas, where it could accumulate over time.
Recent surveys of hundreds of California lakes by state water agencies found that about one out of five lakes in California, including Lake Piru, have high levels of mercury. Of the lakes sampled in a 2009 report, 74 percent had levels of mercury high enough that fish were unhealthy to eat three or more times a week. About 26 percent had even higher levels, leading the state Office of Environmental Health Hazard Assessment to warn against consumption of fish from such waters by children or pregnant women. Advisories have been issued on consuming fish from many popular California waters, including Lake Nacimiento, Clear Lake, and San Francisco Bay.
Some of these mercury-laden lakes are near areas of gold mining, where mercury was used to enhance the recovery of gold in the 19th century, or near abandoned mercury mines, but the contaminated lakes in Southern California are far from known mining sites. Searching for the source of this mercury, Weiss-Penzias and his team first collected samples of rain water, but when the Moss Landing Marine Laboratories tested the samples, they found low levels of mercury — about .1 percent per trillion.
Knowing that sediments on the ocean floor can have high levels of mercury left by atmospheric deposition, from both volcanoes and the burning of fossil fuels, and that these deposits are brought to the surface by strong upwelling currents during the spring and summer, Weiss-Penzias and his team looked for other means the neurotoxin could be transferred from the ocean inland.
"The upwelling begins in March and goes through July or August," Weiss-Penzias explained. "The rain ends in April, so there's not an overlap there. So what about the fog, because it rolls in throughout the summer, and it has closer contact with the ocean?"
The researchers found far more mercury than they expected.
"We found the typical amount of mercury and methylmercury that one usually finds in rain," explained Christopher Conaway, one of the researchers. "The surprise is that methylmercury is so much higher in coastal fog."
The researchers found an average of about 3 parts per trillion in fog, roughly 20 times the amount in rain, with big spikes of methylmercury, the organic form of the material. The source is not known, although deposits in the ocean are suspected, because no human sources for mercury between Monterey and Big Sur have been identified.
"This is a preliminary result that's very surprising," said Mark Stephenson, at the Moss Landing Marine Laboratories, where water samples are sent for mercury testing from around the state. "We don't know the significance of the finding yet, but I think it will open up a whole new area of research."