What's Safe Mercury Facts Mercury finds its way into the atmosphere from natural processes such as volcano eruptions, groundwater seepage and evaporation from the oceans as well as human activity. The latter accounts for between 50 and 75 percent of total releases to the air each year, according to the latest estimates. An estimated 243 tons of mercury gets pumped into U.S. air each year from human activities. Of this amount, combustion sources contribute 85 percent. By far the least mercury-polluting fossil fuel is natural gas, which contains almost no mercury at all.
Oil is the next cleanest, followed by coal, the dirtiest.
Once released into the environment, mercury can be recirculated through the air, soils and water for extremely long periods, possibly even hundreds of years. Total global atmospheric mercury has at least doubled during the industrialized age and may have increased five-fold since 1890. EPA found mercury in fish at 92 percent of more than 314 water bodies tested across the nation. Mercury use by industry in the U.S. has been in a steep decline for decades, with the peak year thought to be 1970. Dramatic reductions in the use of mercury in the manufacture of paint, pesticides and batteries are credited with the decline.