The Japan Probe website has a new post on the changing maximum radiation limits in Japan. "Several weeks ago, the Japanese government raised the acceptable maximum annual radiation dosage standard for children from 1 millisieverts to 20 millisieverts (about 3.8 microsieverts a day). The decision outraged many parents, who feared that the new standard meant that their children would be exposed to unhealthy levels of radiation. The Education Ministry initially responded by stating that there was non intention to allow 20 millisieverts of exposure, and that it actually expected that exposure to children would not exceed 10 millisieverts of radiation a year."
In past posts here, I have mentioned this problem and the need for more realistic standards for radiation. Despite what anti-nuclear groups say, there is solid scientific evidence that low dosages of ionizing radiation are not harmful. I have even given reasonable standards based on areas of the world with much higher background radiation and limits that are applicable to workers in nuclear technologies. Thanks to science fiction, uneducated anti-nuclear activists and government agencies of questionable competence, there will continue to be needless confusion on what is allowable without detectable increase in health risk.
"Although radiation may cause cancers at high doses and high dose rates, currently there are no data to establish unequivocally the occurrence of cancer following exposure to low doses and dose rates – below about 10,000 mrem (100 mSv). Those people living in areas having high levels of background radiation – above 1,000 mrem (10 mSv) per year – such as Denver, Colorado, have shown no adverse biological effects." The above is taken from the US Nuclear Regulatory Commission radiation fact sheet. Ten milliSieverts per year is 2.7 MicroSieverts per day or 0.114 microSieverts per hour.
In the same face sheet, the average US background radiation is 310 millirem per year or 3.1 milliseiverts per year or 0.85 microseiverts per days or 0.04 microseiverts per hour. Now for school children in Fukushima the goal is 1 milliseivert per year, 0.27 microseiverts per day or 0.01 microseiverts per hour.
Explaining the real impact of radiation to parents, after a nuclear accident, is not something I envy. But if the Japanese can reduce radiation exposure in Fukushima Prefecture to 1 tenth the background of Denver, Colorado and less than one third the normal background radiation in the United States, more power to them.
The Japan Times had the same story. Between the two sources there appears to be some confusion. By using 1 millisievert per year the Japanese nuclear regulators appears to be sticking with the US NRC guideline of 1 millisievert per year over normal background. Perfectly reasonable under most situation, but a bit overly conservative for Fukushima Prefecture. Their proposed target of 10 mSv per year is much more realistic and proven safe by studies of Denver, Colorado.
For concerned parents, the 20 mSv per year upper limit may be high from a comfort level view, but there is no indication that it is unsafe. Adult nuclear energy works have a 50 mSv per year limit with no ill effects and less than half that limit should not pose a problem for children. The only question really for children is infants, which have not been a large test group for obvious reasons.
Potatoes from Japan are in the news with low levels of radiation. The difference in radiation standards will continue to rear its ugly hear. In the Thai article, sweet potatoes were test at nearly 16 Becquerel per kilogram which is well be low the Thai limit of 100 Bq/kg. Japan has a limit of 500 Bq/kg for most produce. The arbitrary limits varying between nations should be realistically addressed.
While Bananas and Brazil nuts are fairly commonly known to have radiation levels, potatoes are also a background radiation contributor, with levels of 125 Bq/kg not uncommon. Hypersensitivity to radiation after an incident is common and can only be combated with education before an incident. Now Thailand is planning to destroy perfectly safe sweet potatoes once they determine a safe means to destroy a safe food. Yes, it is a little stupid, but every nation has to deal with their lack of proper standards and public trust.
The new tuber terror has spurred the media to look up reports on the potential for potatoes to absorb radiation as they grow. None of the reports I have seen mention that adding potassium fertilizer to the soil decreases the amount of radioactive Cesium 137 the potatoes absorb, much like iodine tables reduce the human bodies absorption of radioactive iodine.
It would nice if some trusted, if there is one, government agency published the average radiation levels of foods and recommended radiation limits so more countries could get on the same page.
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