Figure 9. Periodic table of the elements. The 76 elements found in coal are highlighted by colors with regard to their general abundance in coal, as follows: blue, major elements (generally greater than 1.0 percent in abundance); red, minor elements (generally greater than or equal to 0.01 percent); and yellow, trace elements (generally less than 0.001 percent). Pursuant to the Clean Air Act Amendments of 1990 (Public Law 101-549), the U.S. Environmental Protection Agency (EPA) studied fifteen of these elements as potentially hazardous air pollutants (HAPs); green bars in their boxes indicate those fifteen elements. Thirteen of the original were cleared when the EPA found that there was no compelling evidence that they cause human health problems; a green bar across the bottom of the box indicates those elements. Two elements from the original fifteen, mercury (Hg) and arsenic (As), indicated by a green bar across the centers of their boxes, are still under study—mercury as a HAP and arsenic as a potential pollutant in ground water that flows through fly-ash and coal-mine spoil piles. Subsequently, in December 2000, EPA found that mercury emissions from coal-fired power plants require regulation; EPA will propose regulations in 2003 and issue final rules in 2004. Modified from Periodic Table of the Elements (Sargent-Welch Scientific Company, 1979), used with permission.

U.S. Department of the Interior, U.S. Geological Survey
URL: https:// pubsdata.usgs.gov /pubs/circ/c1143/html/fig9.html
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