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Fukushima-derived radionuclides in the ocean and biota off Japan
Edited by Karl K. Turekian, Yale University, North Haven, CT, and approved February 24, 2012 (received for review December 19, 2011)

Abstract
The Tōhoku earthquake and tsunami of March 11, 2011, resulted in unprecedented radioactivity releases from the Fukushima Dai-ichi nuclear power plants to the Northwest Pacific Ocean. Results are presented here from an international study of radionuclide contaminants in surface and subsurface waters, as well as in zooplankton and fish, off Japan in June 2011. A major finding is detection of Fukushima-derived 134Cs and 137Cs throughout waters 30–600 km offshore, with the highest activities associated with near-shore eddies and the Kuroshio Current acting as a southern boundary for transport. Fukushima-derived Cs isotopes were also detected in zooplankton and mesopelagic fish, and unique to this study we also find 110mAg in zooplankton. Vertical profiles are used to calculate a total inventory of ∼2 PBq 137Cs in an ocean area of 150,000 km2. Our results can only be understood in the context of our drifter data and an oceanographic model that shows rapid advection of contaminants further out in the Pacific. Importantly, our data are consistent with higher estimates of the magnitude of Fukushima fallout and direct releases [Stohl et al. (2011) Atmos Chem Phys Discuss 11:28319–28394; Bailly du Bois et al. (2011) J Environ Radioact, 10.1016/j.jenvrad.2011.11.015]. We address risks to public health and marine biota by showing that though Cs isotopes are elevated 10–1,000× over prior levels in waters off Japan, radiation risks due to these radionuclides are below those generally considered harmful to marine animals and human consumers, and even below those from naturally occurring radionuclides.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: kbuesseler{at}whoi.edu.
Author contributions: K.O.B., S.R.J., and N.S.F. designed research; K.O.B., S.R.J., I.I.R., H.B., Z.B., C.F.B., J.G., A.M.M., H.M., J.N., S.M.P., and S.Y. performed research; C.F.B. and S.M.P. contributed new reagents/analytic tools; K.O.B., S.R.J., N.S.F., I.I.R., H.B., Z.B., C.F.B., E.M.D., J.G., A.M.M., H.M., J.N., S.M.P., and S.Y. analyzed data; and K.O.B., S.R.J., N.S.F., and I.I.R. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: Data reported in this paper and from the cruise is available from the Biological and Chemical Oceanography Data Management Office, http://osprey.bcodmo.org/project.cfm?flag=view&id=186.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1120794109/-/DCSupplemental.
Freely available online through the PNAS open access option.