Toxic mercury in the arctic, long thought to be coming primarily from atmospheric sources, is also being carried into the region by rivers, U.S. scientists say. While the atmospheric source has long been studied, new research suggests twice as much mercury actually comes from the flow of circumpolar rivers that carry the element north into the Arctic Ocean, Harvard University researchers reported Monday. \"The arctic is a unique environment because it\'s so remote from most anthropogenic (human-influenced) sources of mercury, yet we know that the concentrations of mercury in Arctic marine mammals are among the highest in the world,\" Harvard scientist Jenny A. Fisher said. \"This is dangerous to both marine life and humans. The question from a scientific standpoint is, where does that mercury come from?\" The most important rivers flowing to the Arctic Ocean are in Siberia: the Lena, the Ob, and the Yenisei. Mercury emission from gold, silver, and mercury mines in Siberia may be polluting those rivers, researcher said. The Arctic Ocean is shallow, which increases its sensitivity to input from rivers, they said. \"The environmental implications of this finding are huge. It means, for example, that climate change could have a very large impact on arctic mercury, larger than the impact of controlling emissions to the atmosphere,\" Fisher said. \"More work is needed now to measure the mercury discharged by rivers and to determine its origin.\"