Iodine-129 in Seawater Offshore Fukushima: Distribution, Inorganic Speciation, Sources, and Budget

摘要

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 ~(129)I in seawater depth profiles collected offshore Fukushima in June 2011. Significantly elevated ~(129)I concentrations in surface water were observed with the highest ~(129)I/~(127)I atomic ratio of 2.2×10~(-9) in the surface seawater 40 km offshore Fukushima. Iodide was found as the dominant species of ~(129)I, while stable ~(127)I was mainly in iodate form, reflecting the fact that the major source of ~(129)I is the direct liquid discharges from the Fukushima NPP. The amount of ~(129)I 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 ~(129)I 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 ~(129)I from the Fukushima accident was estimated. These Fukushima- derived ~(129)I data provide necessary information for the investigation of water circulation and geochemical cycle of iodine in the northwestern Pacific Ocean in the future.