Iodine-129 in seawater offshore fukushima: Distribution, inorganic speciation, sources, and budget

The Fukushima nuclear accident in March 2011 has released a large amount of radioactive pollutants to the environment. Of the pollutants, iodine-129 is a long-lived radionuclide and will remain in the environment for millions of years. This work first report levels and inorganic speciation of ¹²⁹I in seawater depth profiles collected offshore Fukushima in June 2011. Significantly elevated ¹²⁹I concentrations in surface water were observed with the highest ¹²⁹I/¹²⁷I atomic ratio of 2.2 × 10^-9 in the surface seawater 40 km offshore Fukushima. Iodide was found as the dominant species of ¹²⁹I, while stable ¹²⁷I was mainly in iodate form, reflecting the fact that the major source of ¹²⁹I is the direct liquid discharges from the Fukushima NPP. The amount of ¹²⁹I directly discharged from the Fukushima Dai-ichi nuclear power plant to the sea was estimated to be 2.35 GBq, and about 1.09 GBq of ¹²⁹I released to the atmosphere from the accident was deposited in the sea offshore Fukushima. A total release of 8.06 GBq (or 1.2 kg) of ¹²⁹I from the Fukushima accident was estimated. These Fukushima-derived ¹²⁹I data provide necessary information for the investigation of water circulation and geochemical cycle of iodine in the northwestern Pacific Ocean in the future.