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."
|Contact: Vince Stricherz|
University of Washington