Selenium

Selenium was discovered in 1817 by the Swedish chemist Jöns Jacob Berzelius and his assistant Johan Gottlieb Gahn while they were investigating the byproducts of sulfuric acid production from pyrite. Berzelius realized that it was a new element due to its unique properties and decided to name it 'selenium' after the Greek word 'selene,' meaning moon, in reference to tellurium, whose name derives from 'tellus,' meaning earth. Its elemental form was shown to exhibit both metallic and non-metallic properties. Over the years, selenium's properties have been explored extensively, and it garnered scientific interest for its role as a semiconductor and its biological significance.

Selenium is found in nature primarily in minerals and ores that contain sulfide minerals. It is commonly associated with metals such as copper, lead, and silver, and is most often extracted from the byproducts of copper refining. In the earth's crust, selenium is relatively rare, occurring at an average concentration of approximately 0.05 mg/kg. It has also been identified in various forms of soil and water, where its availability is influenced by geochemical conditions. Notably, selenium is present in certain plants, such as garlic and broccoli, which can accumulate higher levels of this element in their tissues.

Selenium is an essential trace element that plays a vital role in human health. It is a key component of several enzymes, particularly glutathione peroxidases and thyroid peroxidases, that are crucial for protecting cells from oxidative damage and regulating thyroid hormone metabolism. Deficiency in selenium has been linked to various health issues, including compromised immune function and certain types of cancer. Moreover, it has been observed that adequate selenium intake is necessary for proper reproduction and heart function. The element is found in various foods including nuts, seafood, and grains, highlighting its importance in a balanced diet.

Selenium is a grey, non-metallic element that exhibits a crystalline structure. It possesses a melting point of 221 °C and a boiling point of 685 °C. In its most stable form, gray selenium, it exhibits a shiny metallic luster and conducts electricity when exposed to light, making it useful in photovoltaic cells. It can form various allotropes that display different physical properties. Chemically, selenium is reactive and can combine with numerous elements to form compounds. It typically exists in oxidation states ranging from -2 to +6, with the most common compounds being selenides, selenates, and selenites, which have importance in both chemical and biological contexts.

Selenium has a wide range of applications in various industries. It is primarily used in glass manufacturing to improve the clarity and reduce color distortion. Furthermore, selenium is significant in the electronics industry, where it is used in the production of photovoltaic cells for solar energy conversion, photocopiers, and light meters. Its use as a dietary supplement is growing as it is recognized for its antioxidant properties, contributing to health benefits when consumed in appropriate amounts. Additionally, selenium compounds are employed in agriculture as fertilizers to enhance soil selenium levels in crops.

• Selenium is sometimes found in the hydrogen selenide gas, which has a smell similar to that of rotten eggs.
• Certain species of bacteria can use selenium as an energy source, which plays a crucial role in the biogeochemical cycling of nutrients.
• The amount of selenium in food can vary significantly depending on the selenium content of the soil in which the food was grown.
• Some researchers are investigating the potential of selenium as a therapeutic agent for HIV and certain types of cancer.