For years, scientists have assumed that if mercury is high and increasing in fish in the North American and European Arctic, the same is true of fish elsewhere in the Arctic. But a team of scientists from the U.S., Russia, and Canada has discovered that assumption is wrong in much of the continental Arctic.

In addition to differences in mercury processes as a result of diverse atmospheric, geological（地质的）, and biological conditions, "It turns out that the economic decline of the former Soviet Union, which collapsed in 1991, appears to have been good for the Arctic environment in that part of the world," said Leandro Castello, an assistant professor of fish and wildlife conservation in the College of Natural Resources and Environment at Virginia Tech.

He is the first author of a study to be published in today's (Dec. 20) issue of Environmental Science & Technology, a journal of the American Chemical Society.

Atmospheric mercury comes largely from mining and ore processing, such as smeltering（熔炼者）, according to a United Nation's environmental program study. Under certain water conditions, mercury is converted to a special form that can be absorbed by living organisms, through a process called methylation（甲基化）.

"Methylmercury is highly toxic," said Castello.

But the research team determined that burbot fish in two Russian rivers, the Lena and the Mezen, are safe to eat.

The fish from these rivers were compared to burbot from 20 locations along the Pasvik River on the Norwegian-Russian border and along the Mackenzie River in Canada, where decades of studies have found high levels of mercury that make the fish unsafe.

Burbot are cod-like fish found in fresh waters throughout the Arctic. They are long-lived, eat other fish, and are non-migratory.

"The burbot（淡水鳕） fish was chosen because they are top predators that integrate many bio-geo-chemical processes in the river watersheds（流域，水域）," said Castello. "The fish were collected downstream of the watersheds, so that they would present everything that happened upstream."

Sampling was done using an ice-fishing method in the peak burbot season, November and December, by co-author Alexander V. Zhulidov of the South Russian Centre for Preparation and Implementation of International Projects.

"We developed and led an initiative of biological monitoring of the water quality of major rivers of Russia in 1980 and continued to do it until 2001, because we knew it could provide useful information one day. In 2002 the funding was cut and the program was closed. Unfortunately we have no funding to continue collecting such interesting data," said Zhulidov.