Thawing Arctic permafrost may well unleash a new wave of toxic mercury pollution, say scientists, contributing to ongoing mercury poisoning issues in parts of the region.

Mercury poisoning harms wildlife and causes developmental and neurological damage in human fetuses and children.

These soils were frozen year round as recently as 10 to 20 years ago, but now thaw and re-freeze annually, said lead author Dwayne Elias, a microbiologist with the Oak Ridge National Laboratories, a federally-owned research center in the United States.

As the freeze-thaw cycle continues in coming years, he said, bacteria that contain the genes needed to convert inorganic mercury to its toxic form, called methyl mercury, will “wake up from being dormant for thousands and thousands of years.”

Groundwater will transport this methyl mercury into rivers and streams that game animals such as moose and caribou drink from, he said. Those water flows will also carry the mercury into coastal habitats of marine mammals and fish.

Inert mercury is carried into the Arctic by global wind and water currents from sources in lower latitudes, largely coal-fired power plants and small-scale gold mining in Asia and Southeast Asia.

There have also been cases of mercury poisoning caused by pollution and illegal waste dumping from industrial operations sited in the Arctic, such as the “Ontario Minimata disease” crisis among First Nation communities in Ontario, Canada in the 1960s and 1970s.

Methyl mercury poisoning is a longstanding problem in the North American Arctic.

One recent study found that Inuit women and children in some remote northern Quebec communities consumed mercury at nearly twice the government’s recommended maximum daily dose. The children scored five points lower on IQ tests, on average, than Arctic children who ate less of traditional foods including beluga whale, seal, and walrus meats. The poisoned children also needed remedial education four times more often than children from less-remote villages.

Scientists in 2014 reported high levels of toxic mercury among residents of two coastal communities in Greenland.

In a 2004 study conducted in the sub-Arctic Faroe Islands of the North Atlantic, children born to mothers who ate pilot whale meat while pregnant had impaired cognitive abilities, hearing, and heart health throughout childhood and into their teen years.

For the latest research, which was published Friday in the journal Science, Elias and his colleagues tested over 3,500 “metagenomes” for the presence of methylating genes. Metagenomes are data sets that include the combined genetic codes of every organism present in an environmental or other biological sample.

Over 2,000 metagenomes in this study came from “a comprehensive sample of terrestrial and aquatic environments” around the world, said Elias, while around 1,200 were from human and animal sources.

“In permafrost, there was data existing from a couple of permafrost sites in Alaska,” he said. “We were able to find not only that the mercury methylation genes were present in those samples, but that they gave us some of the highest counts in all of the thousands of samples.”