Mercury concentration in fish is much lower than expected in much of the continental Arctic, and the Soviet Union may have something to do with it.

A team of scientists from the U.S., Russia, and Canada has discovered that in addition to differences in mercury processes as a result of diverse atmospheric, geological, and biological conditions, the socialist state involuntarily helped the Arctic.

"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," Leandro Castello, an assistant professor of fish and wildlife conservation in the College of Natural Resources and Environment at Virginia Tech, said in a statement.

Atmospheric mercury comes largely from mining and ore processing, such as smeltering, 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.

Until the 1970s, atmospheric mercury were on the rise as a result of industry in Europe and in North America, but began to decline from those sources due to emission controls, with Asia coming on line as a source, the paper explains.

In Russia, metallurgic industries in Murmansk region and smelter companies in the Pasvik watershed explain high levels of atmospheric mercury in the Pasvik River. The economic decline near the watersheds of the Lena and Mezen lowered polluting activity there, researchers said.

Researchers said "there are no ancillary environmental data from the time period of the study in Russia," but they suggest the differences across the Arctic "may be explained by differences in water quality, geological bedrock formations, and proximity to polluting sources."

The research team determined that burbot fish, cod-like sea creatures found in fresh waters throughout the Arctic, in two Russian rivers, the Lena and the Mezen, are safe to consume.

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.

"The burbot fish was chosen because they are top predators that integrate many bio-geo-chemical processes in the river watersheds," 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 the study's co-author Alexander V. Zhulidov of the South Russian Centre for Preparation and Implementation of International Projects.

Mercury concentrations from fish in the Mezen River were lower than 10 locations, but higher than eight in North America, while mercury levels in burbot in the Lena River were among the lowest.

"Good news since the Lena River is one of the largest watersheds in the world," said Castello.

Mercury concentrations from fish in the Mezen and Lena rivers also were found to have been on a decline by 2.3 percent a year, whereas in North America they have been increasing by 5 percent a year.

A confounding factor has been climate change, Robert Spencer, an associate scientist at the Woods Hole Research Center, said in a statement. In burbot in the Canadian Arctic, mercury concentrations in fish tissue have increased despite declining atmospheric concentrations because rising temperatures appear to increase availability of mercury to fish populations.

"More studies are needed in the Russian Arctic if we are to better understand how mercury moves through this type of environment," Castello said.