IT'S ELEMENTAL!
SELENIUM AT A GLANCE
SELENIUM LIU TUNGSHENG, CHINESE ACADEMY OF SCIENCES, BEIJING
I
N I 9 3 5 , A T E R R I B L E DISEASE WAS
sheep's heart. This was noted as similar to
the pathological changes seen in Keshan spreading wantonly in some rural ardisease patients. The cause of the white eas of Heilongjiang province in northmuscle disease was attributed to selenium eastern China. Women of childbeardeficiency in the environment. And, ining age and children were its primary deed, by adding appropriate selenium in victims. Particularly cruel, the disease frethe form of Na 2 Se0 3 , white quently occurred without warnmuscle disease can be treated ing and led to the death of a large and prevented in sheep. So we number of people. At the time, had a clue for investigating Kenobody understood the cause of shan disease in humans. this disease, so it was called "Keshan disease" because it was first For the next 10 years, Chinese reported in Keshan County of scientists studied Keshan disease Heilongjiang province. Today, in three ways. First, they used Keshan disease is known to be fluorospectrophotometry with 0ELE8&ATIN0 C&Stt'S an endemic myocardial disease. 2,3-diaminonaphthalene to de80TH It still occurs in some rural areas. termine trace levels of selenium. ANJtiVEftSARY Simultaneously, a multidiscipliThe idea that environmental nary research team consisting of selenium deficiency could be the both Earth and medical scientists was escause of Keshan disease came about as the tablished and studied environmental geolresult of the discovery of a special ecologogy, geochemistry, geography, hydrology, ical phenomenon in the Keshan disease resoil science, epidemiology, nutrition, and gion. In the summer of 1967, my colleagues pathology The investigation plan was based and I went to Heilongjiang province to inon a unique geo-ecological phenomenon vestigate the geological and geochemical that I had previously discovered, that is, environment of the disease districts. We that Keshan disease has a distribution that were surprised to learn that local residents forms a belt crossing China from northeast to southwest. The belt region is a transitional area from the eastern plane, which has a wetter climate, to the western mountains, which are drier and where weathering and leaching actions are strong and both loss of water and soil erosion are serious problems. Aresearch team took samples of rock, soil, E P I D E M I C Map of the distribution of Keshan disease on water, and staple food the Chinese mainland, showing a belt crossing the country grains (corn, wheat, milfrom the northeast to the southwest. let, and so on). Human hair specimens were obbelieved that Keshan disease was coming tainedfrompeople who lived in the disease from the local water and soil, because, they districts and in the nondisease districts. A reasoned, a person could avoid the disease number of chemical components, includby moving from the disease district to aning selenium and more than 10 other trace other place. In particular, we were told by elements, as well as some organic coma local veterinarian that sheep in the dispounds, were analyzed. The data indicated ease district were contracting white musthat the concentrations of selenium are lowcle disease. The main pathological change er in the disease-district samples. for white muscle disease is injury of the So we suggested that adding selenium to 94
C & E N / S E P T E M B E R 8. 2 0 0 3
Name: From the Greek setene, moonAtomic mass: 78.96. History: Discovered in 1817 by Swedish chemist Jons Jakob Berzelius after analyzing an impurity that was contaminating the sulfuric acid being produced at a factory in Sweden. _ _ Occurrence: Occurs naturally in the rare minerals eucairite, crooksite, and clausthalite. Obtained commercially as a by-product of copper refining. Appearance: Exists as two atlotropes: red and gray. Red selenium, the less stable of the two, is an amorphous powder; gray selenium is a silvery metal. Behavior: Burns in air, but is unaffected by water. Although ordinarily a poor conductor of electricity, gray selenium is a photoconductor, meaning it becomes an excellent conductor in the presence of light. Uses: Used In photoelectric cells, photocopiers, solar cells, and semiconductors. Because it is a powerful photoconductor, gray selenium is valuable as a light sensor and is used in robotics, light-switching devices, and light meters. Compounds containing selenium are useful in controlling dandruff and are often added to shampoos.
the diets of local residents could halt the spread of Keshan disease. Chinese medical scientists carried out a series of animal studies designed to determine the metabolic, toxicological, and biochemical characteristics of selenium supplementation. On the basis of the results of these studies, residents of disease-prone districts took supplements of Na 2 Se0 3 under medical supervision. At the same time, a series of biochemical and environmental observations were made. Ten years' worth of data show that taking Na 2 Se0 3 tablets is an effective measure for controlling the spread of Keshan disease. While we still do not know for certain whether selenium deficiency is the only factor leading to Keshan disease, it is certainly one of the most important factors. And we can also say that lack of selenium in the environment is potentially harmful to the health of humans and animals and is thus worth our attention. Liu Tungsheng is a researchprofessoratthe Institute of Geology & Geophysics, Chinese Academy ofSciences, Beijing. Hong Yelang, aprofessor at the Institute of Geochemistry, Chinese Academy ofSciences, contributed to this essay. HTTP : / / W W W . C E N - 0 N L t N E . O R G
