Selenium mobilization during Rain-Soil Interaction at Etna volcano

Abstract

Humans are attracted by the fertile properties of volcanic soils. Currently around 10% of the world population lives within active volcanic areas. Volcanoes emit enormous amounts of potentially toxic elements, even in the absence of obvious volcanic activity. Selenium is particularly interesting due to it geochemical similarities with sulphur, a major compound in volcanic gasses. Although selenium (Se) is an essential element for humans, ingestion of an excess amount of Se can produce adverse effects. Mt. Etna, the biggest volcano in Europe, is persistently active for the last 200,000 years. It is one of the most intensely monitored volcanoes. In the area, volcanic gasses, rainwater and groundwater are enriched in selenium. Although soils play an important role in the Se level in food and water and thereby human health, the behaviour of S! e in Etnean soils is currently unknown. We studied the Se sorption during rainwater-soil interaction in batch experiments with soils and synthetic rainwater with different pHs. Our results show spatial trends with soil sample location. Trace element deposition from the plume cannot explain the observed elemental patterns. Moreover, Fe oxides do not control the geochemical Se cycle in this environment. However, the stage of soil development and especially the presence of Al compounds and organic matter play an important role in the behaviour of Se. These results have implications for the chemical composition of the aquifer. In addition, the mobility of Se influences the bioavailability and potential toxicity through agricultural activities, essential to the local economy.