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	Mercury is an element on the periodic table. It occurs naturally in the environment in some types of rocks. It can be released rapidly by the eruption of volcanoes and slowly by rocks and soils. Humans have been speeding up the release of mercury from these sources by digging up and burning fossil fuels. On average, scientists estimate that about three times more mercury falls from the sky now than before the Industrial Revolution.&nbsp;</div>
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	It is useful to have a general picture of the sources of mercury. In the U.S. in 1999, anthropogenic (caused by humans) sources of Hg to the atmosphere were emissions from coal-burning power plants (40%), industrial boilers (10%), burning hazardous waste (5%), and chlorine production (5%).&nbsp;<br />
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	The U.S. and other developed countries have worked to decrease these releases of mercury since 1999. However, over the past few decades, emissions of mercury from developing countries have increased, offsetting decreases from developed countries.&nbsp;<br />
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	Once it&rsquo;s emitted to the atmosphere from smokestacks and the like, mercury has a long residence time in the atmosphere, estimated at up to a year. This makes mercury a global problem, with emissions able to circle the globe and land in remote areas that don&rsquo;t emit large amounts of mercury such as the arctic &ndash; or Maine. Though Maine releases less than a thousandth of a percent of US emissions, many ecosystems and biota in Maine and the Northeast have been found to be contaminated with mercury.&nbsp;<br />
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	There are a few factors that contribute to the mercury contamination problem. Scientists believe that it&rsquo;s because Maine and the Northeast are downwind of a lot of the large coal-burning power plants in the mid-western US. Also, some of our ecosystems are probably more sensitive to mercury contamination &ndash; they have a lot of forested areas, which capture mercury from air, and a lot of wetlands, where naturally-occurring bacteria convert mercury to its toxic form. However, almost all US states have some kind of mercury fish consumption advisory, and it&rsquo;s an issue for many National Parks, including Everglades in Florida, Isle Royale &amp; Voyageurs in the upper Midwest, Yellowstone, Kejimkujik in Nova Scotia, and many more. Scientists are still learning the extent of the mercury problem, and it&rsquo;s hard to compare Maine to other places though the Northeast is thought to have many &lsquo;hotspots&rsquo; of mercury contamination.&nbsp;<br />
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	Finally, it only takes a very small amount of mercury to contaminate an ecosystem. It&rsquo;s what&rsquo;s called an &lsquo;ultra-trace&rsquo; substance &ndash; usually measured at the parts per billion or parts per trillion levels. A little mercury goes a long way, because it is eventually passed up the food chain and bioaccumulates.</div>
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