Recent reports in the popular press cite evidence for contamination of tuna and other fish by unnatural radionuclides released after the Fukushima nuclear disaster. These reports occasionally assert possible consequences to human health, usually without context or reference to rigorous, evidence-backed models. Some reports state that the mere presence of these elements is dangerous without explaining that many of the methods employed (e.g. ICP-MS) are capable of detecting them in processed samples in trace or even parts per trillion quantities, below the levels of at which any effects to human health should be reasonably predicted, and far below the levels of naturally occurring radioactive elements such as polonium 210.
Ken Buesseler of the Wood Hole Oceanographic Institution has compiled an authoritative FAQ explaining the nature of the measurements, worthy of study by legislators and consumers alike. Below are some links to the primary literature, including a 2013 PNAS paper by Fisher et al., “Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood,” stating
Radioactive isotopes originating from the damaged Fukushima nuclear reactor in Japan following the earthquake and tsunami in March 2011 were found in resident marine animals and in migratory Pacific bluefin tuna (PBFT). Publication of this information resulted in a worldwide response that caused public anxiety and concern, although PBFT captured off California in August 2011 contained activity concentrations below those from naturally occurring radio- nuclides. To link the radioactivity to possible health impairments, we calculated doses, attributable to the Fukushima-derived and the naturally occurring radionuclides, to both the marine biota and human fish consumers. We showed that doses in all cases were dominated by the naturally occurring alpha-emitter 210Po and that Fukushima-derived doses were three to four orders of magnitude below 210Po-derived doses. Doses to marine biota were about two orders of magnitude below the lowest benchmark protection level proposed for ecosystems (10 μGy·h−1). The additional dose from Fukushima radionuclides to humans consuming tainted PBFT in the United States was calculated to be 0.9 and 4.7 μSv for average consumers and subsistence fishermen, respectively. Such doses are comparable to, or less than, the dose all humans routinely obtain from naturally occurring radionuclides in many food items, medical treatments, air travel, or other background sources. Although uncertainties remain regarding the assessment of cancer risk at low doses of ionizing radiation to humans, the dose received from PBFT consumption by subsistence fishermen can be estimated to result in two additional fatal cancer cases per 10,000,000 similarly exposed people.