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From the Earth to the Moon

The element selenium was named after the Goddess of the Moon, Selene. Yet selenium has nothing to do with the moon.

No, this story is not about space travel. It is about the naming of elements, specifically, selenium, discovered by the Swedish chemist Jons Jacob Berzelius in 1817. He named it after Selene, the Goddess of the Moon. One might therefore assume that selenium has some connection to the moon, but it doesn’t. The element has no lunar link, but on earth, selenium-bearing minerals are often found together with tellurium-bearing minerals. When Berzelius discovered selenium, tellurium was already known, and had been named after Tellus, the Roman Goddess of the Earth. Since tellurium and selenium seemed to go together, just like the Earth and the Moon, Berzelius named the new element after the moon goddess.  

Selenium is a very rare element in the earth’s crust, but an important one. There are no selenium mines, the element is obtained as a byproduct when ores of copper, sulfur, iron or lead are mined. Due to its semiconductor properties, selenium finds extensive use in the manufacture of transistors. It is also a photoconductor, meaning that it can change light energy into electrical energy, a property that is extensively used in the photocopying industry. Trace amounts of selenium are also added to glass to give it clarity, and larger amounts can be added to achieve a ruby red colour.   

Selenium is even found in the human body, incorporated into various enzymes. A prime example is glutathione peroxidase, responsible for eliminating hydrogen peroxide, a potentially dangerous substance formed during normal metabolic processes. If the peroxide is not eliminated, it can end up being converted to nasty free radicals that can wreak havoc with health. Selenium therefore is an essential trace element that must be acquired from the diet. We don’t need much of it, the total body load is only about 14 milligrams, and all we need is about 65 micrograms a day to prevent deficiency. Since selenium is widespread in foods, with whole wheat, Brazil nuts, fish and peanuts being particularly rich, deficiency is unlikely, but not impossible.   

Studies have suggested that people living in areas where the soil has relatively little selenium, as in parts of the Southern U.S., may indeed be deficient, and may even be more prone to certain cancers, such as prostate, because of a lack of detoxicating enzymes that rely on selenium. Some researchers recommend a daily supplement of about 100 micrograms, but there is no evidence that people who follow this regimen have lower cancer rates. Large doses of selenium, although certainly not the amounts found in supplements, can produce an objectionable garlic-like breath odour. In fact Berzelius, selenium’s discoverer, was alerted to this by his housekeeper who complained to the master about his bad breath. He was probably emitting dimethyl selenium that formed in his body from transdermal absorption of the selenium compounds with which he was working.


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