Thus, it ranks in abundance between silver and gold. The element has a number of industrial uses, some of which stem from its unusual light sensitive properties. For example, it is used in office copiers the familiar Xerox machine and in electric door openers. It is also used in the manufacture of pigments, pharmaceuticals, rubber and glass. The industrial source of selenium is the copper refining industry and about 1 million pounds are used annually in the United States.
Selenium is present in varying degrees in soils throughout the world.
In some areas, levels are quite low but in other areas, such as in the Great Plains and Rocky Mountain regions and in Venezuela, levels are high. Certain wet, organic soils in Ireland are reported to contain 850 ppm. Selenium in the soil is present in many forms which vary greatly in availability to plants. The element is often present in uranium deposits and prospectors have used the so called selenium accumlator plants to aid them in their search for that rare element. In the 1800's, what was later to become known as selenium toxicity was reported in U.S. Army horses in the Nebraska territory.