A new approach to evaluate factors controlling elemental sediment–seawater distribution coefficients (Kd) in coastal regions, Japan

Abstract

In numerical models to simulate the dispersion of anthropogenic radionuclides in the marine environment, the sediment–seawater distribution coefficient (Kd) for various elements is an important parameter. In coastal regions, Kd values are largely dependent on hydrographic conditions and physicochemical characteristics of sediment. Here we report Kd values for 36 elements (Na, Mg, Al, K, Ca, V, Mn, Fe, Co, Ni, Cu, Se, Rb, Sr, Y, Mo, Cd, I, Cs, rare earth elements, Pb, 232Th and 238U) in seawater and sediment samples from 19 Japanese coastal regions, and we examine the factors controlling the variability of these Kd values by investigating their relationships to hydrographic conditions and sediment characteristics. There was large variability in Kd values for Al, Mn, Fe, Co, Ni, Cu, Se, Cd, I, Pb and Th. Variations of Kd for Al, Mn, Fe, Co, Pb and Th appear to be controlled by hydrographic conditions. Although Kd values for Ni, Cu, Se, Cd and I depend mainly on grain size, organic matter content, and the concentrations of hydrous oxides/oxides of Fe and Mn in sediments, heterogeneity in the surface characteristics of sediment particles appears to hamper evaluation of the relative importance of these factors. Thus, we report a new approach to evaluate the factors contributing to variability in Kd for an element. By this approach, we concluded that the Kd values for Cu, Se, Cd and I are controlled by grain size and organic matter in sediments, and the Kd value for Ni is dependent on grain size and on hydrous oxides/oxides of Fe and Mn.