Exploring Rare Earth Elements in Groundwater: Advancements in Analytical Techniques and Implications for Sustainable Resource Management

Groundwater is an important natural resource that provides drinking water for millions of people around the world. Recently, there has been a growing interest in the presence of rare earth elements (REEs) in groundwater. These elements have unique properties that make them essential components in a wide range of technological applications. The occurrence of REEs in groundwater is of particular interest because it represents a potential new source of these valuable elements. Traditional sources of REEs, such as mining and processing of ores, are associated with significant environmental impacts, making the discovery of REEs in groundwater an attractive alternative. Furthermore, the presence of REEs in groundwater can provide insights into the geochemical processes that occur in the earth's crust. Despite the potential benefits, the presence of REEs in groundwater also raises concerns about the environmental and human health impacts of their extraction and use. However, the concentrations of REEs in groundwaters are very low (often below the detection limits) making them poorly considered. We proposed an improved method for the determination of REEs in groundwaters, measured through inductively coupled plasma-mass spectrometry (ICP-MS) The samples underwent a selective enrichment process which is based on the coprecipitation of REEs with Mg(OH)₂, assisted by the triethylamine (TEA). The samples come from groundwater of the lower flanks of Etna Volcano (Sicily, Italy). Our data show a general trend of the shale-normalized patterns, left-dipping with negative anomalies in Ce and positive anomalies in Y, highlighting a major complexation of the heavy REEs respect with to the light ones. The concentrations of REEs in Etnean groundwaters are totally controlled by the HCO₃- complexation. Moreover, the Y/Ho molar ratio, positively correlated with the total alkalinity of the samples, suggests a selective release of Y possibly derived by the dissolution of secondary calcite. Despite the low concentrations, the health risk for the population should not be underestimated, as we are dealing with drinking water. Further studies are still in progress.