Abstract
The leaching behavior of arsenic (As), lead (Pb), nickel (Ni), iron (Fe), and manganese (Mn) was investigated from subsurface core sediment of marine and nonmarine depositional environments in central Kanto Plain, Japan. A four-step sequential extraction technique was adopted to determine the chemical speciation, potential mobility, and bioavailability of metals under natural conditions in variable depositional environments. In addition, a correlation of these properties with pore water and total metal content was carried out. The concentration of As in pore water was found to be 2–3 times higher than the permissible limit (10 µg/L) for drinking water and leachate in fluvial, transitional, and marine environments. The trend of potential mobile fractions of As, Pb, and Ni showed Fe–Mn oxide bound > carbonate bound > ion exchangeable bound > water soluble in the fluvial environment. However, in the marine environment, it showed Fe–Mn oxide bound > water soluble > carbonate bound > ion exchangeable bound for As. The leaching of As in this fluvial environment is due to the organic matter-mediated, reductive dissolution of Fe–Mn oxide bound, where Mn is the scavenger. The amount of total content of As and sulfur (S) in transitional sediment reflects an elevated level of leachate in pore water, which is controlled by S reduction. However, the leaching of As in marine sediment is controlled by pH and organic matter content.
Highlights
Soil and sediment, which play a key role in geochemical cycling, are widely known as the sink and source of potentially hazardous trace metals [1]
A lithological column was performed after correlating with the relevant references of nearby areas and collecting physicochemical data of the sediment samples, e.g., visual observations of the color, particle size distribution, electrical conductivity, and S content (Figure 2)
Marine sediment thickness was confirmed from the electrical conductivity (EC) value, S content, the presence of marine shell fragments, and correlation with other references [30,32,43,44]
Summary
Soil and sediment, which play a key role in geochemical cycling, are widely known as the sink and source of potentially hazardous trace metals [1]. Metals are bound with soil or sediment particles by a variety of mechanism with different metal phases. Sequential extraction analysis has become the most widely used method to determine precise chemical speciation, leaching behavior, and the potential mobility of metals in sediment [3,4,5,6]. It is known as “operationally defined” when selected chemical reagents are used to extract metal from different phases or bindings of the soil/sediment particles [7,8,9,10,11]
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