20 Nov (NucNet): The combined dose of caesium-134 and caesium-137 from eating a typical restaurant-sized portion of Pacific bluefin tuna contaminated by radioactivity from the Fukushima-Daiichi nuclear plant in Japan is only about five percent of the dose acquired from eating one uncontaminated banana, a study says.
The study, published by the National Academy of Sciences of the United States of America, says consumption of a typical serving of 200 grams of tuna contaminated with 4.0 becquerels per kilogramme (Bq/kg) dry weight of caesium-134 and 6.3 Bq/kg dry weight of caesium-137 – the mean values for Pacific bluefin tuna caught off San Diego in August 2011 – resulted in committed effective doses of 3.7 and 4.0 nanosieverts (nSv – one billionth of a sievert) respectively.
“To put this into perspective, the combined dose of 7.7 nSv from these two caesium isotopes is only about five percent of the dose acquired from eating one uncontaminated banana and absorbing its naturally occurring potassium-40 (K-40), and only about seven percent of the dose attributable to the K-40 in the tuna.
More strikingly, the study says, the dose from both caesium isotopes is only 0.2 percent of that attributable to the naturally occurring polonium-210 from ingesting the fish.
In August 2012, Pacific bluefin tuna off California were found to have less than half the levels of radioactive caesium that were found in August 2011, which would result in even lower doses to human consumers, the study says.
The study shows that the committed effective dose received by humans based on one year’s average consumption of contaminated Pacific bluefin tuna from the Fukushima-Daiichi accident is comparable to, or less than, the dose we routinely receive from naturally occurring radionuclides in many food items, medical treatment, air travel or other background sources.
The study says publication of the news that radioactive isotopes originating from Fukushima-Daiichi had been found in migrating Pacific bluefin tuna resulted in a worldwide response that caused “anxiety and concern”.
The news was covered by more than 1,100 newspapers worldwide and numerous internet, television, and radio outlets. Such widespread coverage reflects the public’s concern and general fear of radiation, the study says.
Calculations in the study are based on Pacific bluefin tuna because it is the species the media became most alarmed about when Fukushima-contaminated samples were caught off the coast of California.
The report is online: www.pnas.org/content/early/2013/05/30/1221834110.full.pdf
