Distribution coefficients (K d) of stable iodine in estuarine and coastal regions, Japan, and their relationship to salinity and organic carbon in sediments

Abstract

The sediment-water distribution coefficient, (K(d)), is one of the most important parameters in radionuclide assessment models. In this study, we determined K ds of stable iodine (I) in estuarine and coastal regions. We studied 16 estuarine and coastal regions of Japan and obtained I data on water and sediments. Data on salinity, pH, dissolved organic carbon and dissolved oxygen in water, and organic carbon (OC) in sediments were also obtained as estuarine variables. Determined (K(d))S of I in the Sagami River estuary decreased along the salinity gradient (salinity range, 0.1-33.8), indicating that salinity is one of the important factors controlling the (K(d)) values; however, when the (K(d)) values were compared among all the estuaries, the difference between minimum and maximum (K(d)) values varied by about two orders of magnitude in a narrow salinity range of 30.0-34.4. A significant correlation between (K(d)) value and OC content in sediments was observed in all the stations with a salinity of ≥ 30 except for stations in the Ishikari and Onga River estuaries. The exceptions are probably due to different sources of the sediments, which are explained by the results of relatively low I/OC ratios in sediments in those two estuaries, compared to the other estuaries. Thus, OC in sediments as well as salinity may be responsible for the variation of (K(d))S of I in the estuarine and coastal regions.