The European Shale: An improved data set for normalisation of rare earth element and yttrium concentrations in environmental and biological samples from Europe

Abstract

The distribution of the Rare Earths and Yttrium (REY) in shale is considered representative of that of average Post-Archean upper continental crust regardless of the shale's origin. Hence, shale is commonly used to normalise the REY concentrations of vastly different sample types ranging from chemical sediments and seawater to atmospheric dust and river water, and, in particular, environmental and biological samples. However, discussions with non-specialists such as journalists, decision makers in industry and politics, and the general public are often hampered by their serious doubts that normalisation to Australian or North-American shales produces meaningful results for samples from Europe. Hence, we present REY data for aliquots of the same European Shale composite that had originally been prepared and studied in the mid-1930s by E. Minami under supervision of V.M. Goldschmidt and that is well-established in the geoscience literature. We determined REY concentrations by different methods of sample preparation (acid-pressure digestion and laser-induced flux-free fusion) and analysis (solution ICP-MS and LA-ICP-MS on glass beads) with excellent precision and accuracy. This improved and complete REY data set (Y: 31.9, La: 44.3, Ce: 88.5, Pr: 10.6, Nd: 39.5, Sm: 7.30, Eu: 1.48, Gd: 6.34, Tb: 0.944, Dy: 5.86, Ho: 1.17, Er: 3.43, Tm: 0.492, Yb: 3.26, Lu: 0.485; all concentrations in mg kg−1) is recommended for shale-normalisation of natural materials that originate from Europe. This will simplify discussions with media and broader public, for example when reporting on REY as emerging microcontaminants. Examples given include coastal seawater (North Sea), river water (Rhine River), tap water, waste water treatment plant effluent, marine and freshwater mussel shells, and mushrooms.