selenium [Se]

Introduction

From the Greek selene meaning moon. Discovered in 1817 by Swedish chemist Jons Jakob Berzelius. He as analyzing an impurity that was contaminating the sulfuric acid being produced at a factory in Sweden.

Occurrence

• occurs naturally in the rare minerals eucarite, crooksite & clausthalite
• obtained commercially as a by-product of copper refining

Characteristics

• nonmetallic element that resembles sulfur & tellurium chemically
• exists as 2 allotropes: red & gray
• red selenium
  • less stable than gray selenium
  • amorphous powder
• gray selenium
  • stable gray silvery metal
  • varies in electrical conductivity with the intensity of its illumination (photoconductor)
• burns in air, but is unaffected by water

Uses

• essential element, RDA 55 ug/day
  • occurs in selenoproteins
  • selenium deficiency is known as Keshan disease
• dandruff shampoos
• electronic devices
  • photoelectric cells
  • solar cells
  • semiconductors
• light sensor
  • robotics
  • light-switching devices
  • light meters

Pathology

(Toxicity)

• excess supplemental selenium may increase risk of diabetes recommendation: not to exceed 400 ug/day, < 200 ug/day may be more prudent
• selenium supplements increase risk of non-melanoma skin cancer

Notes

• high-selenium yeast supplements do not improve lipid profiles

More general terms

• trace element

More specific terms

• selenium-75

Additional terms

• periodic table
• selenide
• selenium measurement
• selenium sulfide (Selsun, selenium disulfide)
• selenocysteine
• selenomethionine
• selenoprotein

Component of

• Souvenaid; Fortasyn Connect

Database

• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=107674