Regional variations in wet and dry deposition fluxes of trace elements in Japan

The annual wet and dry deposition fluxes of 12 trace elements (i.e., As, Cd, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se and V) were measured on the basis of 1 year of observations (December 2003–November 2004) at 10 sites in Japan. Precipitation and dry deposition (gases and particles) samples were collected every half month using an automatic sampler, which is composed of a precipitation sampler and a water surface sampler for dry deposition. The wet deposition fluxes of Hg, Pb and Se exceeded their dry deposition fluxes at most sites. In contrast, the dry deposition fluxes of Cr, Cu, Mn, Mo, Ni and V were significantly higher than their wet deposition fluxes. The annual wet deposition fluxes of trace elements except for Cu, Mo and Ni were correlated with the annual precipitation amount (P<0.05P<0.05). In particular, about 70–80% of the variance of the wet deposition fluxes for Hg (r2=0.80r2=0.80), Sb (r2=0.68r2=0.68) and V (r2=0.80r2=0.80) was explained using the precipitation amount. The wet deposition fluxes of As, Cd, Pb and Se at sites on the Japan Sea coast tended to be higher than those expected from the precipitation amount. This suggests a large contribution of their long-range transport from the Asian continent. On the other hand, the regional variations in the dry deposition fluxes of the trace elements were different from those in the wet deposition fluxes. A markedly higher dry deposition fluxes were observed at sites in industrial and urban areas. The relatively high dry deposition fluxes of Cr, Cu, Mn, Ni and Pb suggest that these elements are mainly from electric steel furnaces near the sites, because they are abundant in furnace emission particles. The results of lead isotope analyses indicate that the lead isotope ratios in the dry deposition samples at industrial and urban sites are different from those at other sites. This implies that lead dry deposition at such sites is dominated by emissions from peculiar sources, although whether those sources are the electric steel furnaces is unknown.