Selenium — the story of an element
Today everyone knows that selenium is a valuable trace element. It is included in vitamin complexes produced by leading manufacturers, possesses antioxidant properties, and is believed to have rejuvenating effects on the human body. Selenium deficiency has been associated with numerous disorders, including metabolic disturbances, cardiovascular diseases, and cancer.
However, this was not always the case. The history of studying the physiological significance of selenium for humans has been long and controversial. For a long period, selenium was considered an exclusively harmful element. The first evidence of its toxicity dates back to ancient times. As early as 1295, the traveler Marco Polo, while journeying through Tibet, described cases of horse poisoning manifested by the loss of manes and tails after the animals consumed local plants. Of course, at that time nobody knew the word “selenium”. More than 500 years later, in 1817, the element was discovered by the Swedish chemist and mineralogist Jöns Jacob Berzelius. Therefore, the cause of the toxicity of Tibetan flora was identified much later.
From the time of its discovery until the middle of the 20th century, generations of scientists focused exclusively on the toxic properties of selenium in their research. This perception was first questioned in a study conducted by American scientists in 1957. Later, it was established that both humans and animals require selenium for normal functioning. The need for selenium depends on age, sex, region of residence, health condition, and physiological characteristics of the body. According to the World Health Organization, in selenium-deficient regions specific pathological conditions may develop when daily selenium intake falls below 21 μg for adult men and 16 μg for women. Insufficient selenium intake in humans and animals causes a type of trace element deficiency known as hyposelenosis. One of its characteristic manifestations in domestic animals is muscular dystrophy. In the 1930s, a disease characterized by severe myocardial damage (the heart is also a muscle) was described in China’s Keshan Province. The disease became known as Keshan disease, or selenium-deficiency cardiomyopathy.
Today it is known that selenium is a substance with a very narrow range between beneficial and toxic effects. It is an essential trace element for the human body; however, excessive intake may be harmful and can lead to hyper-selenosis, hair loss, joint deformation, and general exhaustion of the body. All of this has attracted considerable interest in selenium among geologists, medical researchers, and agricultural specialists.
Selenium is a dispersed element whose industrial reserves are associated with sulfide deposits. It is currently known that its average content in the Earth’s crust is about 5×10⁻⁶% by mass. Natural selenium compounds occur mixed with sulfides in copper-zinc pyrite, copper-cobalt, and polymetallic ores. The largest selenium reserves are associated with magmatic copper-nickel, hydrothermal copper-molybdenum, copper-pyrite, and infiltration selenium-uranium-vanadium deposits. Almost all selenium is extracted from such deposits, where its concentration in ores ranges from 0.04% to 0.004%.
While studying the impact of selenium on humans and the environment, specialists compile maps of the selenium status of territories, attempting to correlate disease incidence with selenium concentrations in environmental components. Due to the highly developed agricultural sector of Ukraine, the level of selenium availability largely depends on the geochemical properties of soils. In Ukraine, the soils most depleted in selenium are found within the Polissia landscape-bioclimatic zone. However, nowadays selenium deficiency is being successfully addressed. Interestingly, Ukrainian scientists have even proposed distinguishing a separate subtype of polymetallic mineral waters — selenium-bearing mineral waters. In particular, such a deposit has been identified in the Kirovohrad region, and there is also information about similar occurrences in the Carpathian region.
Thus, an element once classified as a first-class hazard has become, in a sense, a remedy for a wide range of diseases. The history of selenium research clearly demonstrates how new scientific knowledge transforms our understanding of the world.
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