Selenium is another example of an element that is essential yet toxic in tiny amounts. From the days of its discovery in 1817 it was known to be an element to avoid, and one of the first to suffer from it was its discoverer, the Swedish chemist Jons Jacob Berzelius. He was alerted to its most noticeable side effect when his housekeeper complained about his appallingly bad breath, accusing him of eating raw garlic. Although he did not realize it, Berzelius was emitting a gas we now know as dimethyl selenium, one of the worst smelling gases ever discovered. Nor was it his only encounter with this obnoxious element. On another occasion he was overcome by breathing hydrogen selenide gas (formula H2Se) which he had prepared without realizing that this gas is deadly. He was ill for two weeks.
Prolonged exposure to selenium, as occurred in some industries, led to anaemia, loss of weight, dermatitis - and social isolation. Selenium was treated as a pariah element, to be avoided if possible. And then in 1975 it was shown to be something we cannot avoid, it was proved to be an essential element for humans. Yogesh Awasthi, based at Galveston in Texas, found that it was part of the antioxidant enzyme, glutathione peroxidase, which eliminates peroxides before they can form dangerous free radicals. Selenium was there to protect the body. In 1991, Professor Dietrich Behne at the Hahn-Meitner Institute in Berlin found selenium in another enzyme, deiodinase, which promotes hormone production in the thyroid gland. Every one of our trillions of living cells contains more than a million atoms of this element, and we have about 14 mg of selenium in our body. The recommended maximum daily intake is 450 ^g; above this we risk selenium poisoning, the most obvious symptoms of which are extremely foul breath and body odour, as we seek to rid ourselves of an unwanted excess.
The daily intake of selenium depends on the foods we eat. The average person takes in about 65 ^g/day, which is enough to prevent selenium deficiency, although it is less than the recommended intake for men of 75 ^g. Selenium levels are highest in hair, kidneys, and testicles, where it is needed to protect sperm. Most people get their selenium from breakfast cereals and bread, especially wholemeal bread, two slices of which will provide up to 30 ^g depending on the soil of the farm from which it came. Foods particularly rich in selenium are Brazil nuts, molasses (black treacle), tuna, cod, salmon, liver, kidney, peanuts, and bran.
There is no evidence that selenium has ever been used as a homicidal agent, nor is it ever likely to be because its tell-tale odour on the breath of the victim would immediately alert those around them to what they had been given.
Was this article helpful?