Dr. Tsubokura's Radiation Lecture Vol.44
Author: Masaharu Tsubokura
Editors: Akihiko Ozaki M.D., Yuki Senoo
87. The levels of radiation contamination in seafood have gradually decreased over time.
Since the 2011 Fukushima Daiichi nuclear accident, regular measurements of radioactive contamination in sea products have been conducted once a week to evaluate the effect of airborne and waterborne radiation on seafood.
These measurements have indicated that, as with air dose rate and agricultural products, the contamination of sea products has gradually decreased year by year.
Furthermore, even in 2016, the radiation contamination of some fish, mainly bottom-dwelling fishes such as dabs and Pacific cod in a particular area of the sea, had reached the level of the reference value.
However, in the survey conducted in the Fukushima prefectural office, a proportion of the fish with contamination of the reference value or above dropped to approximately 0.1%; that is, the survey found only one fish with a contamination level exceeding the reference value in 1000 samples.
In particular, fish that inhabit the sea surface, such as whitebait and ammodytes; migratory species, such as skipjack, tuna, chum salmon, and saury; tentacle species, such as octopus and squid; shrimp; crabs; shellfish; and seaweed are all clarified to be contaminated at the level lower than the reference value in all Japanese prefectures, including Fukushima.
88. Seawater fishes are less likely to accumulate radioactive cesium.
The last article explained that since the 2011 Fukushima Daiichi nuclear accident, regular assessments of radioactive contamination in sea products have been conducted once a week to detect the effect of airborne and waterborne radiation on seafood.
Although the overall level of radioactive contamination in seafood is continuously reducing, as with agricultural products, the absorbed contamination of radioactive substances is different among species.
For example, saltwater fish can discharge cesium more rapidly than freshwater fishes, which means that the contamination of the former is smaller than that of the latter.
Fish and shellfish take in radioactive cesium from water and feed, in the same manner as how they take in minerals such as potassium, sodium, and magnesium. Meanwhile, like humans, their bodies discharge radioactive substances through urine and feces.
Because saltwater fish are surrounded by an environment that has a higher concentration of minerals than their body fluids, minerals inside saltwater fish are naturally discharged outside of their bodies, whereas freshwater species retain minerals inside their bodies.
Thus, seawater species are less likely to absorb the radioactive cesium contaminates compared to freshwater species.
----------------------------------------------------------------------------------------------------------
The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on September 4th and 11th 2016 was reproduced for MRIC Global under the author's permission.