In a project funded by the Swiss National Science Foundation, the biochemist has been trying to identify the origins of selenium on the European continent. To this end, she and her team collected weekly rain samples over a period of two years on the Jungfraujoch in the Bernese Oberland and on the Pic du Midi in the French Pyrenees. In these two remote spots, it is unlikely that the composition of the rain will be influenced by local sources such as factories. But “we would not be able to draw conclusions as to the source on the basis of the selenium analysis alone”, says Winkel, which is why she developed a new process.
Her first step was to identify, in collaboration with climate scientist Heini Wernli at ETH Zurich, where the weekly precipitation largely came from. She established that rain in summer primarily comes from the Eurasian continent, and in winter from the Atlantic. At the same time, the researchers were measuring relatively high concentrations of selenium in spring, summer and autumn, and a lower concentration in the cold season. The second step of their research was to analyse the chemical species of selenium, iodine, sulphur and bromine in the rain samples, as well as the proportion of the C-13 isotope in the carbon.
Taking all of these parameters into consideration alongside the weather models has enabled the researchers to make deductions about the origin of atmospheric selenium for the first time: “It appears that the continental biomass represents a major source during the summer”, says Lenny Winkel. That is quite astounding, as it has always been assumed that the origins were marine to some extent, and, to a larger extent, anthropogenic. “For a definitive conclusion however, the rainwater would need to be sampled at shorter intervals instead of just once a week”, says Winkel.