[MTT51-04] Distribution and geochemical behavior of anthropogenic rare earth elements in two coastal environments
Keywords:rare earth elements, coastal environments, Gd anomaly
Seawater samples were collected in Tokyo Bay and Ariake Sea, and the samples were collected in the rivers flowing into Tokyo Bay and Ariake Sea. To decompose the organic ligands, the samples were measured after UV-irradiation. Iron hydroxide co-precipitation method was used for collection of REE. To determine REE concentrations in river water and seawaters accurately, we applied the isotope-dilution method. After removing Fe from the anion exchange column, REE concentrations were determined by an inductively coupled plasma-mass spectrometer (ICP-MS). The REE concentration was normalized by using PAAS (Post-Archean Average Australian Sedimentary rock). Moreover, Gd anomaly was calculated by Gd/Gd* = GdSN/(0.33SmSN + 0.67TbSN) (Bau and Dulski, 1996). GdSN, SmSN and TbSN are relative values of gadolinium, samarium (Sm) and terbium (Tb) that were normalized by PAAS, respectively.
Large Gd anomaly was detected in river samples flowing into Tokyo Bay. The vertical distributions of REE were clarified in Tokyo Bay and Ariake Sea. Gd anomaly was detected mainly in Tokyo Bay. The contrasting REE composition implies the anthropogenic REE were supplied to Tokyo Bay. In the area surrounding Tokyo Bay, huge amount of Gd might be released probably because of medical use.
There were no clear differences in REE composition and Gd anomaly in Tokyo Bay between this study and the previous studies, (Nozaki et al., 2000). We will discuss the factors controlling the distribution of REE in these areas.
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