What is selenium
Selenium is a chemical element that belongs to the chalcogens group, also known as the ore formers, along with oxygen, sulphur, tellurium, and polonium. Native selenium in its elemental form is rare, as are selenium minerals like clausthalite and naumannite. Selenium is found in sulphur-containing copper, lead, zinc, gold and iron ores as a metal selenide. The element has various forms, including red, black, and grey selenium.
Nickel and copper production involves industrial extraction, which leads to the formation of metallurgical by-products. Organic selenium compounds can be found in yeasts, bacteria, and plants. Yeast can bind selenium, making it a helpful ingredient in producing selenium for food supplements. Selenium has many applications, including being used as a feed and fertiliser additive, as a colouring agent in the glass industry, in photovoltaics (solar cells), medicine, cosmetics, photography, and manganese production.
How does selenium get into drinking water?
Pure selenium is typically insoluble in water, although some selenium compounds can dissolve in water. Agricultural practices such as drainage can dissolve selenium from the soil, altering its natural distribution and causing it to enter the water cycle through surface evaporation. Most of the selenium in the atmosphere comes from industrial sources. Rainfall can distribute selenium throughout the water cycle. High concentrations of selenium in grasslands can cause significant problems for grazing animals. Certain plant species can accumulate selenium in harmful quantities, which can lead to serious animal diseases if consumed by grazing livestock.
How does Selenium affect the human body?
As an essential trace element, selenium is a building block of the amino acid selenocysteine. It is required for the production of thyroid hormones. It is supplied with food. Depending on the type of selenium compound, the organism processes and stores the substance differently. The total content in the body is between 10 and 20 mg. Selenium-rich foods include meat, offal, milk, eggs, fish and seafood. Some plants are specialised in selenium; the selenium-accumulating Brazil nut is particularly rich in selenium. The concentration in food depends on the selenium content of the soil. Because the natural selenium content is insufficient for agriculture, it is often added to dairy cattle feed as a precaution.
Selenium is a radical scavenger, i.e. it protects the organism from damaging free radicals. However, this assumption is still controversial due to different medical studies. The biochemical function still needs to be fully clarified in many areas, just like the optimal selenium requirement. However, there are proven selenium deficiency diseases (Keshan disease, Kaschin-Beck disease, anaemia, arthritis, premature ageing), partly with degenerative disease patterns. Extremely unbalanced diets, veganism and various organic disorders can be causes of selenium deficiency.
Depending on the selenium concentration, deficiency symptoms or toxic abnormalities can occur. Selenates and selenites, the salts of selenic acid and selenous acid, are dangerous. Direct skin contact and inhalation of selenium air should be avoided because of the risk of selenium poisoning (selenosis). Symptoms of selenosis include garlicky bad breath, persistent fatigue, stomach problems and hair loss. Workers in the selenium-processing glass, paint and electronics industries are exposed to this health risk. Long-term studies have confirmed the carcinogenic and gene-changing effects.
It is astonishing that selenium is toxic even in relatively small quantities (from 450 micrograms) but can also ward off poisons such as arsenic, cadmium, mercury and thallium in the body.
Drinking water polluted by selenium: What to do?
There is no specific limit value for selenium in drinking water in Great Britain in the Drinking Water Regulations and the corresponding legislation in Scotland, Wales and Northern Ireland. These regulations mainly set quality standards for parameters such as microbiological contamination, heavy metals and other chemical substances. Still, they do not include a specific limit for selenium.
However, it is essential to note that water utilities in the UK strive to ensure drinking water quality and maintain selenium levels at acceptable levels. Precipitation, ion exchange, and adsorption with activated carbon filters make it possible to remove selenium from wastewater.
Have water tested for selenium
The guarantee of first-class drinking water is provided by the respective regional water supplier, the municipal utility. They supply water by the Drinking Water Ordinance up to the house connection. Well operators in rural areas surrounded by agricultural land should always keep an eye on the selenium content of the well water. Does the raw water come from a catchment area with a low selenium content? How high the selenium and other contents (e.g., lead, nitrate, nitrite, ammonium, phosphate, bacteria) are in your tap water can only be precisely answered by a water test. A sample taken directly from the tap, analysed by a certified laboratory, gives you clear information about the quality of the most important foodstuff.