Kathy Davis, age 10, of Buford, Georgia, for her question:
What is selenium?
Selenium is one of the earth's basic elements. It is one of nature's rare chemicals, which is lucky for all of us. Traces of selenium in the soil of certain areas has been known to poison whole herds of cattle. It has, however, special uses in electrical equipment and even in medicine.
In the last century selenium was identified as a criminal chemical and little was done to add anything more to this information. Its atoms make up less than 1/100,000th part of the earth's crust, though certain areas have more than their fair share. Cattle in the Dakotas and Montana, Nebraska and Colorado, Kansas and New Mexico were going down with a miserable sickness called "alkali disease" or "blind staggers." Scientists traced the trouble to the presence in the soil of small traces of selenium.
The chemical was absorbed by grasses. Cattle feeding on this and other vegetation of the region became painfully, sometimes fatally, poisoned. The eyes became teary and blind; the joints were weakened, causing the animals to stagger. The poison also damaged the liver, kidneys and other internal organs. Cases of similar poisoning were discovered in people who had eaten contaminated food such as milk, eggs and vegetables produced in regions where unusual amounts of selenium were present in the soil.
Later, selenium was more thoroughly investigated as a basic chemical element. And the poisonous criminal turned out to have some other very surprising qualities. It is classed with sulphur and oxygen in a family of non metal elements. Yet selenium exists as both a metal and a nonmetal. It may be in the form of dark grey, metallic rods or dark red powdery crystals. In the field of electricity, selenium behaves like a metal, though rather an odd one.
Metals such as copper are called good conductors because they freely conduct electric current. Glass, which blocks electric current, is a poor conductor. All conductors vary in quality with heat to some degree. But the conducting qualities of selenium vary with a mere beam of light. This information gave new meaning to the strange element and a series of useful duties. Nowadays, selenium is used to trigger electricity on and off in sensitive instruments. It is used in light meters and TV cameras, solar batteries and' photoelectric cells.
Selenium also is used to harden rubber products and to add a deep red tint to glass.. And, of all things, the old criminal found a job in the medicine business. Mild solutions of a selenium and sulphur compound are used to treat severe cases of dandruff. However, it is still a poisonous chemical. When used as a medicated shampoo, the dosage must be decided by a doctor and the patient must be warned never to taste it.
Selenium poisoning among cattle is now understood and better controlled. However, as more selenium is used in industry, a new hazard may arise. Waste materials from factories may carry it into surrounding soils and water supplies. From here it could start a new career, this time as a people poisoner. Boards of Health are aware of this hazard and keep a sharp eye on the sewage and waste material from plants that use selenium to manufacture electrical equipment, rubber or glass.