Abstract pnas.1120794109 www.pnas.org/cgi/doi/10.1073/pnas.1120794109
The Tohoku earthquake and tsunami of March 11, 2011, resulted in unprecedented radioactivity releases from the Fukushima Dai-ichi nuclear power plants to the Northwest Pacifc Ocean. Results are presented here from an international study of radionuclide con- taminants in surface and subsurface waters, as well as in zooplank- ton 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 cal- culate 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 advec- tion 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 iso- topes are elevated 10–1,000× over prior levels in waters off Japan, radiation risks due to these radionuclides are below those gener- ally considered harmful to marine animals and human consumers, and even below those from naturally occurring radionuclides. |