Selenium is a powerful antioxidant, belonging to the group of trace elements that is vital for our bodies. It helps prevent the development of certain cancers and heart disease, and helps combat cholesterol and osteoarthritis.

But while it is essential in trace form, the situation changes when its concentration increases. The European drinking water limit is set at 10 microgrammes per litre. This is a precautionary value, and it is difficult to set a more precise value because there are relatively few epidemiological studies. What we do know, however, is that selenium is toxic in higher doses.

For 20 years, an American biologist has been studying the disappearance of fish from Belews Lake in North Carolina, which borders a coal-fired power station. Very early on, these fish began to show significant malformations in various parts of their bodies (skeleton, head, eyes, etc.). 95% of the species disappeared within a few years, and more than twenty years later, high concentrations of selenium are still found in the sediments and in the food chain of surviving fish...

Selenium pollution is insidious because there is no sudden death and it often goes unnoticed. It is a geogenic pollutant, meaning that it is naturally present in the rock and passes into the water when boreholes are drilled to collect water. It is also an indicator of the use of water tables that are too deep. And this is unfortunately a current trend. In fact, in order to better protect ourselves from the ever-increasing surface pollution, we are tending to dig deeper and deeper.

Another source of this pollution could be industrial or agricultural. The storage of burnt coal-based waste could, through leaching, contribute to selenium contamination. In agriculture, the spreading of sewage sludge or the use of selenium-rich fertilisers could be the source of significant pollution.

Selenium pollution is a worldwide phenomenon, and the pollution of aquatic environments by this substance is just as widespread in towns as it is in the countryside, from plains to mountains, from the most remote forest to the ice caps of the poles. Analyses carried out in natural environments often focus on more common, priority pollutants, but this overlooks the fact that selenium pollution can pose very serious long-term risks for aquatic habitats and fish stocks. It is important for biologists to be aware of this pollutant, because once a natural environment is contaminated with selenium, a cascade of bioaccumulation events follows, making it almost impossible to intervene after the fact.

While you're waiting for real risk management to be put in place, based on water quality objectives to prevent biological impacts as far as possible, you can use the Berkey® water purification system which, with the help of its Black Berkey® filters, eliminates more than 99.9% of the selenium contained in water, as attested by analyses carried out by an independent laboratory.