A doctor at Minamisouma Municipal Hospital near the devastated nuclear power plants has reported on the issue titled above recently. The original data is shown here at the city web site though it is in Japanese.
In summary, when the percentages of the children with Cessium detected with a whole body counter is compared between last summer and this winter, it has decreased from about 50% to 5%. The WBC detects Cessium above 20Bq/kg. The absolute value ranged from below the detection limit to 100Bq/kg. These measurements were much lower than those observed in Chernobyl. The declining pattern was individualized. That is, there were some whose values were declining slower than the others. Those people have had radiation-contaminated foods like the vegetables grown in their own garden farm etc. When they stopped taking those foods, they had the measured values substantially lowered.
This result means the internal radiation, which was not so serious so far, is steadily decreasing in the young generation. The contamination must be from the foods. In Japan, they could get foods produced in the other areas not polluted with the radioactive substances. That may be the reason why the contamination is kept at such level. The author points out that they should monitor the contamination by the other substances like Strontium. They should be careful for the carcinogenicity of radioactive Iodine to children's thyroid glands, which had alrady decayed long before they started maesurements. They should go on monitoring the internal radiation and the possible carcinogenicity the other health issue like heart toxicity as reported in Chernobyl due to the contamination of radiation for years.
I should add some points to this study. The WBC won't detect contamination localized within a body. Some researchers warn that Cessium would be absorbed by the urinary tract epithelium and would accumulate there so that eventually will cause atypism of those cells later. Even if WBC detects low level or undetectable level of internal radiation, this pathological process could take place in the urinary tract. They should follow up this accumulation of Cessium in the urinary tract and the cellular atypism in the urinary sediments.
This study was performed for the generation older than infants and toddlers. I suspect the usual WBC is not applicable to younger children. I have seen, in a TV interview, a person from the devasted area by the nuclear power plant accident complained their children under 3 yeras of age had not undergone any test for internal radiation at all. Those young ones are most vulnerable to the effect of radiation and should never be neglected in such studies. The government should promptly take any measures to observe and protect them from the contamination of radiation through foods as well as their environment.