"Selenium is an essential micronutrient," Lenny Winkel of the Swiss Federal Institute of Aquatic Science and Technology and ETH Zurich told environmentalresearchweb. "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."
With that in mind, Winkel and colleagues from Switzerland, Germany and the UK modelled selenium concentrations in soils on a global scale. The team used a number of machine learning techniques along with existing databases for soil selenium concentrations and information on soil properties, climate variables and geology.
"This work was possible as in the last few years standardized continental or national geochemical surveys have been conducted, in which soil samples have been collected and analysed for total selenium content, in addition to many other elements," said Winkel. "Using these datasets we could identify broad-scale statistical relationships between selenium concentrations and other parameters (soil, climate, geology) and use these relationships to model selenium concentrations in areas where these were previously unknown."
Earlier studies had mainly been small-scale, finding that soil factors like pH, reduction potential and organic carbon content had most effect on selenium concentration. Winkel and colleagues’ analysis, carried out for the years 1980–1999, revealed that climate plays an important role in the large-scale distribution of selenium in soils. So the team decided to model changes in soil selenium concentrations resulting from future changes in climate.
Under moderate climate-change scenarios in the years 2080–2099, the researchers found, nearly 58% of the area modelled (71.9 million square km in total) would have lower soil selenium levels, with an average loss of 8.4%. Around 20% of the area would see minor changes (between + and – 2.5%), whilst the remaining land was predicted to gain selenium. The proportion of croplands predicted to lose selenium was slightly higher, at 66%.
Climate variables such as aridity index, precipitation and evapotranspiration were dominant in affecting soil selenium concentrations, the team believes, because they control leaching from soils.
"However, besides total concentrations of selenium in soils there are many other factors that determine the selenium content of plants," said Winkel, "for example the form of selenium in the soil and the ability of the plant to take up selenium".
Being deficient in selenium also affects the health of livestock. Winkel hopes that the study will raise awareness that concentrations of selenium in soils are dynamic and that the predicted changes may have an effect on the nutritional value of plants. "Furthermore, we hope that our study will help agricultural communities and governments in exploring strategies that increase the contents of selenium in soils, for instance via adjusting soil properties if possible or applying selenium to agricultural soils," she said.
The team’s model had a resolution of 1° so Winkel says it’s now important to look at the influence of local factors such as sources of selenium and soil type on regional-scale concentrations of the element in soil, and how these may change. Sources can be anthropogenic, such as industrial emissions, or natural, such as rocks and biological or volcanic emissions.
"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," Winkel added. "So we are also planning on looking into the link between climate change and levels of other trace elements in soils."
Winkel and colleagues reported their work in PNAS.