Toxic chromium in Europe's aquifers
Hexavalent chromium (Cr(VI)) is a chemical compound found in products ranging from textile dyes to anti-corrosion coatings. Classified as a human carcinogen, Cr(VI) is also naturally present in the soil and rocks of many populated areas around Europe. When chemicals enter the environment from industrial or natural sources, they diffuse, disperse, react with other chemicals or bind to surfaces. The EU-funded SPECHROM (Spectroscopic and computational investigation of chromium binding on pure minerals and Asopos aquifer soils) initiative studied what happens when Cr(VI) enters aquifer groundwater. SPECHROM analysed how Cr(VI) binds to mineral surfaces like ferrihydrite, hematite, corundum and γ-alumina under different conditions. Such binding is important as it can decrease metal concentrations in water bodies to safe levels. From this data, researchers developed models to predict how Cr(VI) is transported through the environment, where it ends up and in what chemical form. They were particularly interested in understanding how Cr(VI) behaves in Greek aquifers containing naturally high concentrations of the metal. Using soil and rock samples collected from five locations in Greece, researchers discovered why Cr(VI) levels are high in groundwater and deep aquifers in these areas. A non-toxic, immobile form of chromium (Cr(III)) was bound by two forms of naturally present manganese, which then converted Cr(III) to the toxic, mobile Cr(VI). By modelling how Cr(VI) is produced and transported in soils containing chromium and manganese, scientists can predict the risk of human exposure. This will help them to develop guidelines and strategies to manage aquifers containing these soils in populated areas throughout Europe.
Keywords
Chromium, aquifers, Cr(VI), geogenic, soil, ultramafic rocks, SPECHROM, chromium binding
