The Spatial and Temporal Variations in Tritium in the North Pacific Over the Past 70 Years and Their Impacts on the Marine Environment and Organisms

To better understand the fate of treated water from the Fukushima Daiichi Nuclear Power Plant (FDNPP) and its potential impacts, this study gathered data regarding tritium in the North Pacific from the past 70 years using field surveys and published literature. With these data, we explore the spatiotemporal distribution patterns of tritium in the North Pacific and the underlying mechanisms of the spatiotemporal patterns. We also discuss the impacts of treated water discharge on marine tritium levels and radiological doses with respect to marine life. The main results include the following: (a) From the 1950s until 2011 (pre-Fukushima), the tritium concentration in the North Pacific declined exponentially, with an effective half-life of 10.66 years. (b) The impact of the FDNPP accident was most pronounced in Fukushima coastal waters, where the average tritium concentration increased 30-fold between 2011 and 2024. (c) From August 2023 to October 2024, the average tritium concentration within 0–1.5 km of Fukushima decreased by 39.1%. (d) During the same period, the tritium concentration increased between 1.5 and 30 km from Fukushima, and the average tritium concentration within this same range from Fukushima increased most significantly from 111.5 ± 91.1 Bq/m³ to approximately 513.2 ± 812.5 Bq/m³. It is predicted that the concentration within the 1.5–3-km range from Fukushima will exhibit a cyclical pattern due to periodic discharges over the next 30–40 years. (e) Current tritium concentrations in local marine waters remain within the safety limits established by internationally recognized standards.