Dr. Tsubokura's Radiation Lecture Vol.38
Author: Masaharu Tsubokura
Editors: Akihiko Ozaki M.D., Yuki Senoo
75. Absence of internal contamination among residents in Fukushima
As of 2016, whole-body counter screening, which is done to evaluate the level of internal radiation exposure, found no internal contamination with radioactive cesium among the local residents in Minamisoma City, Fukushima Prefecture, which is the coastal area to the north of the Fukushima Daiichi nuclear power plant.
In fact, internal contamination was absent in more than 99% of the residents who participated in the screening, irrespective of the nature of the participants (e.g., adults and children). Currently, it is hard to find a local resident with internal contamination by cesium. This is also true with the locally produced rice, vegetables, and fruits.
Consequently, except for the whole-body counter screening conducted in 2011, internal contamination with radioactive cesium was not detected among residents in Minamisoma City. The absence of internal contamination illustrates the fact that the residents were not regularly consuming contaminated food.
Radioactive cesium was not detected in any residents, even if they consumed food without caring about its place of production, even if they consumed diets produced in neighboring places with adequate inspection, and even if they consumed tap water. The reasons for this phenomenon are adequate food inspections and the countermeasures taken to prevent radiation contamination, as well as the decreasing level of radiation.
In the past few years, the level of internal exposure has been maintained at a quite low level. Notably, no internal contamination has been detected at all among the local children in the last few years.
76. Low levels of radiation exposure do not cause adverse health effects
When one hears the phrase "radiation health effect," many people may think of symptoms such as hair loss, nosebleeds, diarrhea, and burned skin (erythema). Indeed, receiving a high level of radiation exposure in a short period leads to the health effects mentioned above and results in having a high risk of developing cataracts in the future. These symptoms are called "deterministic effects" because they will "definitely" appear in everyone who has been exposed to a high level of radiation.
However, it is important to note that the impact of radiation on health is determined by the extent of the exposure dose. These symptoms will only appear when one’s body receives an extremely high level (over several hundred millisieverts or more) of radiation exposure, which damages many cells in one’s body. In other words, these symptoms will not appear in anyone who is not exposed to radiation exceeding the particular level (lower than several hundred millisieverts). As you may know, CT scanning and X-ray examination do not cause hair loss or erythema.
A deterministic effect is a health effect that will occur in everyone who receives a significantly high level of radiation, but conversely, it will not appear in anyone who receives a lower level of radiation exposure.
The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on June 12th and 19th 2016 was reproduced for MRIC Global under the author's permission.