Long-term variations in I seawater concentrations off Fukushima and potential of 129I as an oceanographic tracer for ALPS-treated water

Suzuki, Takashi; Otosaka, Shigeyoshi*; Takata, Hyoe*; Kuwabara, Jun; Nakanishi, Takahiro; Ikenoue, Tsubasa

Environmental Science & Technology, 60(17), p.13123 - 13131, 2026/05

https://doi.org/10.1021/acs.est.5c18263

As a results of the 2011 Fukushima Daiichi Nuclear Power Plant accident, long-lived radioactive I has been released into the environment, with additional releases beginning in 2023 through ALPS-treated water. To study its long-term variation and potential as an oceanographic tracer, I concentrations in seawater off Fukushima were measured from 2012 to 2024. The highest concentration, 44510 Bq/L, was observed in 2013 near the plant. Levels have since declined toward the pre-accident value of 1.7610 Bq/L. Spatial and temporal changes in the I/Cs ratio indicate the influence of small water masses and support its use as a tracer in areas with complex ocean circulation.