OCCURRENCE  OF  SELECTED  TRACE  ELEMENTS1  

ELEMENT CONTINENTAL CRUST DRINKING WATER STANDARD2
AVERAGE RANGE
 Arsenic  1.8   1 to 10 0.05 
 Cadmium 0.2  0.1 to 0.3 0.005 
 Chromium 100  10 to 200 0.10 
 Copper 55 5 to 100 1.3 
 Fluorine 625 300 to 1,000 4.0
 Gold 0.004 0 to 0.006 -
 Iodine 0.5 0.3 to 2.2 -
 Lead 13 7 to 20 0.015
 Mercury 0.08 0.03 to 0.4 0.0002
 Silver 0.07 0.01 to 0.1 0.05
 Sulfur 260 200 to 2,400 250
 Uranium 1.8 1 to 4 -

1 All concentrations are given in parts per million (ppm), which is roughly equivalent to 0.0001 % on a weight per weight basis.
2 Drinking water standards are the maximum concentrations allowed in drinking water to prevent human health problems (e.g.,
   cancer) from developing over 70 years of exposure ("-" means that the element is not regulated).