2018 Volume 69 Issue 1 Pages 1-30
The straightforward and rapid determination of 53 elements in stream sediments using ICP-AES (inductively coupled plasma atomic emission spectrometry), ICP-MS (inductively coupled plasma mass spectrometry), and AAS (atomic absorption spectrometry) were evaluated for the geochemical mapping of isolated islands. Samples of 0.1 g were decomposed with HF, HNO3, and HClO4 at 125–145°C for 3 h to improve the determination of elements, including refractory minerals. The concentrations of rare earth elements (REEs), Nb, and Ta increased by 5–15% on average, and those of Zr and Hf increased by 30% on average. For arsenic determination, 0.1 g samples were digested using a mixed acid solution with an oxidizing reagent (KMnO4) at 120°C for 20 min. Decomposition without using the oxidizing reagent and/or extended decomposition times has been shown to cause a decrease in As concentrations in geochemical reference materials. However, similar As concentrations in stream sediment samples were obtained irrespective of KMnO4 addition and decomposition time. AAS was used to Hg measurement after thermal decomposition of about 50 mg samples without pre-treatment. The estimated concentrations of 53 elements in geochemical reference materials measured using ICP-AES, ICP-MS and AAS were agreement with the recommended values. Thus, it is concluded that the precision and accuracy of the rapid and straightforward analysis for geochemical mapping were satisfactory.
Geochemical features of stream sediments in the isolated islands of the Seto Inland Sea were strongly influenced by the parent lithology distributed in their watershed. Enrichments of Na2O, Al2O3, K2O, Be, Rb, Nb, REEs, Ta, Th and U were observed in sediments from isolated islands with widely underlain granitic rocks. In contrast, MgO, TiO2, V, Cr, MnO, Fe2O3, Ni, and Co were abundant in sediments from Shodoshima Island where mafic volcanic rock had erupted. Extreme enrichments of Cu, Zn, As, Mo, Cd, Sn, Sb, Hg, Pb, and Bi were found in sediments influenced by mineral deposits and anthropogenic activity.
