PSA - information on selenium

www.webelements.com

www.wikipedia.org

www.environmentalchemistry.com

www.atsdr.cdc.gov

Quick Facts:

The name originates from the Greek word 'selene' meaning Moon. Selenium was identified in Stockholm by Jons Jacob Berzelius in 1817 Selenium has similar chemical properties to Sulphur. Selenium is known as an essential element which means it is essential for life in some species, including humans. The average human body contains around 14mg of selenium (about 1/20,000th of an ounce). Selenium is a metallic main group element, found in Group VIb of the periodic table. It can exist in two forms; as a silvery metal or a red powder.

Properties of selenium:

Name of Element : Selenium
Symbol of Element : Se
Atomic Number of Selenium : 34
Atomic Mass: 78.96 amu
Melting Point: 217.0 °C - 490.15 °K
Boiling Point: 684.9 °C - 958.05005 °K
Number of Protons/Electrons in Selenium : 34
Number of Neutrons in Selenium : 45
Crystal Structure: Hexagonal
Density @ 293 K: 4.79 g/cm³
Color of Selenium : grey, red & black

What is selenium?

Selenium naturally occurring element found in trace amounts in pyrites

Main uses of selenium

• In the glass industry to neutralise the green tinge in glass.

• In the semiconductor rectification of alternating current to give direct current.

• In light meters and in the photosensitive drums in photocopiers.

• In television cameras.

How does selenium occur in the environment?

• Selenium is relatively rare but occurs in trace amounts in pyrites.

• Selenium is mostly extracted from the anode mud formed during the electrolytic refining of copper.

• Plants take up selenium from the soil and propagate it through the food chain.

• Selenium is found in water supplies as selenate and selenite.

• Dietry selenium is obtained from nuts, cereals, meat, fish, eggs and mushrooms

How does selenium affect human health?

First identified as an essential trace element in 1957, it has since been established that the all organisms require selenium.

However selenium has a dual status due to its toxicity and there must be careful balance as there is around an 8-fold gap between the average requirement and levels considered at the upper limit of safe intake. Intakes below 400 micro-grams/day are considered safe for almost all individuals.

It has been suggested that low selenium bloods levels are linked to an increased risk of cancer, particularly with regard to lung cancer in groups of smokers with low levels. Clinical trials have been undertaken and more are underway which seem to prove beyond reasonable doubt that selenium reduces the risk of cancer.

The heart does not function well without selenium and studies in a province of China with very low selenium content within the soil have developed a severe type of heart failure, named after this region and called Keshan's disease.