Dr. Tsubokura's Radiation Lecture Vol.45
Author: Masaharu Tsubokura
Editors: Akihiko Ozaki M.D., Yuki Senoo
89. The levels of radioactive contamination in squid, octopus, and shrimp are low.
Since the 2011 Fukushima Daiichi nuclear accident, regular measurements of radioactive contamination in sea products have been conducted once a week.
Although the overall level of radioactive contamination in seafood is continuously decreasing, as with agricultural products, the absorbed contamination of radioactive substances tends to remain in some species, but this is not the case with other species.
In particular, invertebrates, such as mollusk (e.g. squid, octopus, and shellfish) and crustaceans (e.g. shrimp), tend to have lower levels of radioactive cesium inside their bodies compared to other seabed fish. In fact, the radioactive cesium among these species are barely detectable.
In most sea invertebrates, unlike human invertebrates, minerals are able to freely move back and forth between the surrounding seawater and their bodies. Because of this, the concentration of minerals in their body fluids changes according to that in the environment.
Therefore, the level of radioactive cesium among invertebrates decreases instantly, parallel to that of radioactive cesium in the ocean. As the radioactive cesium in the ocean around the nuclear power plant is barely detectable at present, so is the contamination in invertebrates.
90. The majority of radioactive strontium is discharged from fish.
Since the 2011 Fukushima Daiichi nuclear accident, regular measurements of radioactive contamination in sea products have been conducted once a week.
The reference value of radioactive cesium for sea products is determined as 100 Becquerel/kilogram, similar to other agricultural products. This reference value is designed in the following manner: The total internal radiation contamination, both from radioactive cesium and other radioactive substances (e.g. strontium and plutonium), should not exceed 1 millisievert/year when a person regularly consumes food that reaches the reference value.
As with agricultural products, radioactive cesium is the one we have to pay the most attention to among other radioactive substances.
Some people are concerned about the radioactive strontium contamination in small fishes, as strontium tends to accumulate in bones. However, it is known that the enrichment (the ratio of the level of radioactive substances in seawater and the level of radioactive substances of sea species) of radioactive cesium is much higher than that of strontium for fishes. This is because the majority of ingested strontium is discharged immediately without being absorbed in body tissue.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.
----------------------------------------------------------------------------------------------------------
The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on September 18th and 25th 2016 was reproduced for MRIC Global under the author's permission.