http://articles.mercola.com/sites/articles/archive/2005/03/09/mercury-exposure.aspxThough there are many natural sources of mercury emissions such as volcanoes, geothermal springs, geologic deposits and the ocean, human activities may have doubled or even tripled natural amounts of mercury in the atmosphere within the past 150 yearsenCommunityServer 2008.5 SP1 (Build: 31106.3070)