Relationship between trace elements and depositional environments in shallow sediments: a case study from Southern Kanto Plain,Central Japan |
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| Authors: | Masato Ueshima Takato Takemura Takeshi Saito Yoshiharu Ito Shoichiro Hamamoto Hirotaka Saito Toshiko Komatsu |
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| Institution: | 1.Center for Material Cycles and Waste Management Research,National Institute for Environmental Studies,Tsukuba,Japan;2.Geomechanics Lab,College of Humanities and Sciences, Nihon University,Setagaya,Japan;3.Graduate School of Science and Engineering,Saitama University,Sakura–Ku,Japan;4.Graduate School of Agricultural and Life Sciences,The University of Tokyo,Bunkyo,Japan;5.Department of Ecoregion Science,Tokyo University of Agriculture and Technology,Fuchu,Japan |
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| Abstract: | Underground developments such as subways and shopping facilities have been increasing in number and magnitude in the relatively shallow subsurface of many urban areas where the earth materials commonly are composed of marine sediments. Marine sediments can contain significant amounts of toxic trace elements such as arsenic, boron, and lead. Changes in the subsurface environment caused by excavation and construction in underground developments could potentially cause these toxic elements to be dissolved into pore water of the sediments, which might lead to groundwater pollution. The purpose of this study is to investigate correlations among chemical properties of marine sediments, such as pH and electrical conductivity (EC), concentrations of toxic trace elements, and stratigraphic characteristics of the sediments. We selected three sites with different stratigraphic settings in the southern Kanto Plain around the Tokyo Metropolis. We collected core samples from shallow strata at a site in the Arakawa Lowland, southern Saitama, and at two sites in the Musashino Upland, Middle Tokyo. All sites have both marine and non-marine sediments up to 50–60 m in thickness. We determined trace element concentrations in the pore water, pH, EC, and loss on ignition. The results show that (1) the marine sediments tend to have low pH, high EC, and high sulfur concentration compared to the non-marine sediments (2) the concentration of most of the soluble heavy metals vary depending on the concentration of sulfate, the pH, and the formation processes of the strata, (3) the arsenic concentration is not related to sulfur concentration but apparently to Fe and Al concentrations, (4) the boron concentration is not related to any other properties implying that the boron level is independent of and cannot be predicted by common chemical properties, and (5) for all three sites, concentrations of most of the trace elements, EC, pH, and sulfate concentration were correlated with each other. This study shows that the concentration and potential mobilization of many toxic trace elements in marine sediments could be predicted by easily measurable pore water chemical properties such as pH and EC. This could be useful for predicting and avoiding the risk of groundwater pollution during underground development projects. |
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