Temporal trends of 137Cs concentration in seawaters and bottom sediments in coastal waters around Japan: implications for the Kd concept in the dynamic marine environment

Abstract

AbstractRadioactivity concentrations of 137Cs in seawaters and bottom sediments have been measured in the coastal waters off all nuclear power plant sites in Japan. Sediment distribution coefficient (Kd) values obtained before the Fukushima Daiichi Nuclear Power Plant accident were variable and related to the specific surface area of the bottom sediment. A mathematical model suggested that before the accident the Kd values were in the transient state approaching a dynamic equilibrium with a converged Kd value of 1000–1600. Based on a post-accident mathematical model, the apparent Kd reached the maximum of about 104 and then decreased until now, converging to 6 × 103 on average.