Abstract
Heavy metals are very important due to their association with ecological environment issues, especially human health. Core sediments can serve as an unique sink to record historical and current environment contaminations. To assess heavy metal pollution, their concentrations in core sediments collected from Tokyo Palace Moat were measured coupled with sedimentation age determination using 210Pb activity concentrations and chemical speciation to confirm secondary migration of the elements within the sediment column. As a result, a record of metal contamination in Tokyo mainly via atmosphere is developed in core sediments during the period of 1832-2019. The average sedimentation rate was estimated to be 0.38 cm/yr. All the elements showed low concentrations during Edo period, but concentrations of V, Cr, Mn, Cu, Zn, As, Cd, Sn, Sb, and Pb in core sediments abruptly increased after 1870 as contaminants possibly due to the industrial revolution in Japan in Meiji Period. These elements are basically volatile elements, which supports the fact that most of the elements were supplied via air. Most of the elements showed peaks during 1900-1920 and 1940-1950, but became low around 1925 possibly due to the influence by the Great Kanto earthquake in 1923. Quantitative analysis of Zn K-edge XANES indicated that Zn was mainly present as ZnS after 1930s, but as ZnCO3 before 1930s, possibly because sulfur concentration was not sufficient to form ZnS before 1930s. The formation of these insoluble minerals such as ZnS and ZnCO3 assures that the secondary migration of Zn within the core has been minimal. Anthropogenic Mn accumulation in sediments peaked around 1975 in accordance with the period of high economic growth in Japan, but further discussion in needed to identify the source. For the period of 1980-2019, the data of core sediments reflected the result of stricter environment regulations, which lowered the emission of most of the elements. However, heavy metal concentrations in the surface sediments were still greater than the levels at the bottom of the core. It suggests that some anthropogenic depositions via air are still present in Tokyo at present, which are greater than those in Edo Period recorded in the core (1830-1867).
