Selenium deficiency in agricultural soils caused by climate change, finds study

A new study finds that climate change is lowering the amount of selenium in agricultural soils, a potential health risk factor as selenium deficiency has been linked to cardiovascular disease and certain types of cancers.

Found in trace amounts in soils, selenium is a naturally occurring mineral that works as an antioxidant in the body, helping to keep tissues and cells healthy. Studies have shown that selenium plays an important role in immune system and thyroid functioning, with low blood levels of selenium being associated with an increased risk of immune system problems and, according to some studies, certain forms of cancer.

Foods such as nuts, cereal grains, meat, fish and poultry are known to contain healthy amounts of selenium. According to the Dietitians of Canada, the recommended daily dose of selenium is between 55 and 400 micrograms per day (one serving of pasta, for example, contains 20 micrograms of selenium).

Research has shown that the selenium concentrations can differ depending on the aridity and clay content of soils, and with climate change expected to raise temperatures and cause further drying out of agricultural lands, the risk is there for depletion of mineral content, say the researchers behind a new study published in the journal Proceedings of the National Academy of Sciences.

“Selenium content in soils plays a major role in controlling the contents of selenium in crops and meat products and thus dietary intakes, but soil selenium contents are still unknown in many areas around the globe,” says Lenny Winkel, researcher with the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and co-author of the new study, in a statement.

To help understand how climate change might affect selenium levels, Winkel and colleagues from five other institutes developed a global mapping of selenium soil concentrations and used computer modelling and climate change projections to chart selenium depletion over the next one hundred years.

What they found was that roughly two-thirds of the world’s agricultural lands are likely to experience selenium depletion, with 20 per cent experiencing minor changes and nearly 58 per cent losing an average of 8.4 per cent of their selenium. Regions expected to face the greatest depletion include agricultural lands in Europe, the Americas and southern Africa.

The results are concerning, as selenium deficiency already affects about one billion people worldwide. Further losses may push governments to consider active programs to add selenium content to soils, by fortifying fertilizers, for example, a practice already adopted in Finland where selenium concentrations are known to be low.

Winkel says that more work needs to be done on charting how climate change is likely to impact the soil concentrations of various minerals. “As we found that climate–soil interactions are a main factor in governing broad-scale soil selenium distributions, it is likely that other trace elements (essential or non-essential) may also change with changing climate,” says Winkel. “So we are also planning on looking into the link between climate change and levels of other trace elements in soils.”