Selenium was first isolated in 1817 by the Swedish chemists J. G. Gahn and Jöns Jacob Berzelius. Initially, the chemists thought they had found tellurium while studying materials at a plant where sulfuric acid was produced, because of its similar properties. After further study at his lab in Stockholm, Berzelius realized that its properties differed from those of tellurium and concluded that it was a different element, which is why most sources credit him alone as its discoverer.
Berzelius suggested a name for the newly discovered element based on the Greek word "selene," which means moon, because of its similarities to tellurium, which derived its name from the Latin word "tellus," which means Earth. Selenium is classified as a nonmetal and is element number 34 on the periodic table.
Many uses for selenium have been developed, such as in the manufacture of pigments, plastics, paints, ceramics and electronics. It is sometimes alloyed with other metals to make them more machinable. Selenium plays an important role in nutrition and is sometimes added to soil and animal feed.
In excessive amounts, selenium is a health hazard that can cause deformities in animals. In the 1970s, researchers discovered that high levels of selenium in the Kesterson Reservoir in northern California was causing deformities in birds that nested there. Selenium continues to pose environmental challenges, particularly in California.