<http://schema.org/about>
"Until 1970, mercury was not classified as a dangerous compound in the United States. Before the metal was regulated, it was used"^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.treehugger.com/natural-sciences/mercury-levels-on-the-rise-in-lake-erie-after-decades-of-decline.html>