Distribution and Evolution of Fukushima Dai-ichi derived Cs, Sr, and I in Surface Seawater off the Coast of Japan.

The Fukushima Dai-ichi Nuclear Power Plants (FDNPPs) accident in 2011 led to an unprecedented release of radionuclides into the environment. Particularly important are Sr and Cs due to their known health detriments and long half-lives ( ≈ 30 y) relative to ecological systems. These radionuclides can be combined with the longer-lived I ( = 15.7 My) to trace hydrologic, atmospheric, oceanic, and geochemical processes. This study seeks to evaluate Cs, Sr, and I concentrations in seawater off the coast of Japan, reconcile the sources of contaminated waters, and assess the application of Cs/Sr, I/Cs, and I/Sr as oceanic tracers. We present new data from October 2015 and November 2016 off the coast of Japan, with observed concentrations reaching up to 198 ± 4 Bq·m for Cs, 9.1 ± 0.7 Bq·m for Sr, and (114 ± 2) × 10 Bq·m for I. The utilization of activity ratios suggests a variety of sources, including sporadic and independent releases of radiocontaminants. Though overall concentrations are decreasing, concentrations are still elevated compared to pre-accident levels. In addition, Japan's Environment Minister has suggested that stored water from the FDNPPs may be released into the environment and thus continued efforts to understand the fate and distribution of these radionuclides is warranted.