Major and rare earth elements in rainwaters from Japan and East China Sea: Natural and anthropogenic sources

Abstract

Rainwater samples collected from Tokyo and nearby locations in Japan as well as from two locations over the East China Sea have been analyzed for their rare earth elements (REEs) and major ions. The major ion compositions of these samples show the contributions of oceanic, crustal, and anthropogenic sources, and suggest the relative importance of these sources. Rainwater samples collected in Tokyo and Chofu (a town about 8 km from metropolitan Tokyo) have distinctly higher SO 4 2− and NO 3 − content than in rainwater samples from the coastal area and the East China Sea, whereas the major ion compositions of the latter two areas are dominated by sea salt. The rainwater samples also have variable REE compositions, with various enrichment of light REEs over heavy REEs. Rainwater samples from Chofu are significantly enriched in light REEs, whereas those collected in Tokyo have loess or shale-like REE composition. Rainwater from both places, however, has similar major ion compositions. The enrichment of light REEs in the Chofu rainwater samples corresponds to the typical signature of an anthropogenic source. The Y/Ho ratios in these samples are all higher than average crustal values, and in general, increase with increasing enrichment of light REEs. This indicates that physical mixing of crustal and oceanic sources of the REEs cannot account for the variations of the Y/Ho ratios. Furthermore, although the anthropogenic source of the REEs is generally characterized by a high Y/Ho ratio, factors such as particle/rainwater interactions, pH, and speciation of REEs may also be responsible for the variable abundance and fractionation of REEs and Y/Ho in these rainwaters.