I've noticed a significant number of breathless reports of the threat that radionuclides leaking from the damaged Fukushima reactors present to organisms (including humans) resident on the west coast of North America. This brief post is to point out that the risk to humans from the radioactivity added to the Pacific Ocean because of this disaster is very small indeed according to the latest peer reviewed science.
"Fears regarding environmental radioactivity, often a legacy of Cold War activities and distrust of governmental and scientific authorities, have resulted in perception of risks by the public that are not commensurate with actual risks" - Fisher et al. (2013) Proceedings of the National Academy of Sciences.
Radioactivity (e.g. Cesium 134 and Cesium 137) from the compromised Fukushima Daiichi nuclear plant have been detected in bluefin tuna that migrate between Japan and California. Despite the fact that levels of reactor bred isotopes were still well below national food safety limits there was widespread alarm broadcast through various media outlets. There are many outlandish claims being made as to the environmental damage being caused on the west coast or predicted to result from radiation leaking from Fukushima. Some or the more fringe theories are debunked by biologist Andrew Thaler here.
A recently published paper in Proceedings of the National Academy of Sciences by a colleague, Nick Fisher of Stony Brook University, investigated the risk of Fukushima derived radiation to those consuming Pacific bluefin tuna. Their findings indicate that the bulk of radiation dose to human consumers results from naturally occurring Polonium-210 which was roughly 600-fold greater than Fukushima dervied radiocesium isotopes. Indeed, the estimated dose of radioactivity from consuming tuna carrying Fukushima derived isotopes for a year is similar to or less than our annual doses from air travel, terrestrially derived foods, medical treatment and other background sources.
So, despite the local impact of the disaster which is real and should not be downplayed, the amount of radiation likely to be dispersed in ocean currents and distributed in the marine food web will pose little risk or threat to humans.