Weather conditions, long winters and sea spray are stripping toxic mercury from the atmosphere and incorporating it in the fragile Arctic food chain where it is accumulating, new research suggests, Nature Science Update reports this week. Scientists, led by Julia Lu, at the Meteorological Service of Canada and Toronto report that the sudden burst of sunlight after long polar winters drives chemicals in sea salt to react with normally inert mercury vapour in the air, depositing it onto snow. When the snow melts it injects a pulse of mercury into the Arctic ecosystem at a time when most animals and plants are growing fastest. "Just as the Arctic prepares for its two-month growing season, the atmosphere throws down all this mercury," says Alexandra Steffen, a member of the research team. This mercury becomes concentrated as it passes through the food chain and levels are particularly high in Arctic fish and mammals and in the Inuit people of North America who eat them. According to the report scientists have known about the springtime mercury pulse for a few years but this is the first time the mechanism behind it has been revealed. "Nobody expected an atmospheric chemical reaction like this," says Ralf Ebinghaus, an environmental chemist at the Institute for Coastal Research in Geesthacht, Germany. Nature magazine noted that lab studies are under way to establish the exact nature of the mercury-deposition reaction. Other Canadian researchers are also looking at whether the springtime mercury peak shows up in animal and human populations.