interesting analysis by Majia of the recent study of Fukushima children's exposure to radiation:
http://majiasblog.blogspot.fr/2012/07/new-study-on-childrens-exposure-to.html
Sunday, July 15, 2012
New Study on Children's Exposure to Fukushima Radiation Raises More Questions Than It Answers
One of the most distressing aspects of the Fukushima crisis from my perspective is the effort to trivialize the significance of the event by scientists and regulators.
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The most recent effort to trivialize the effect of radiation from Fukushima can be found here:
A primary health concern among residents and evacuees in affected areas immediately after a nuclear accident is the internal exposure of the thyroid to radioiodine, particularly I-131, and subsequent thyroid cancer risk. In Japan, the natural disasters of the earthquake and tsunami in March 2011 destroyed an important function of the Fukushima Daiichi Nuclear Power Plant (F1-NPP) and a large amount of radioactive material was released to the environment. Here we report for the first time extensive measurements of the exposure to I-131 revealing I-131 activity in the thyroid of 46 out of the 62 residents and evacuees measured. The median thyroid equivalent dose was estimated to be 4.2 mSv and 3.5 mSv for children and adults, respectively, much smaller than the mean thyroid dose in the Chernobyl accident (490 mSv in evacuees). Maximum thyroid doses for children and adults were 23 mSv and 33 mSv, respectively.
MAJIA HERE: First, it is noteworthy how small the sample size is in this study: "In total, 62 people aged from 0 to 83 years old (of which accurate information on age was unavailable for eight people) underwent the measurement with informed consent."
MAJIA HERE: Second, the following passage is odd. It acknowledges that some children were in extensively contaminated areas but the study extrapolated their exposure from adults, and fails to tell us whether or not those adults were from the extensively contaminated areas:
"Some children were known to have stayed in heavily contaminated areas from March 11th to 18th. As the most conservative scenario, we estimated the thyroid dose to children, using the atmospheric I-131 concentration assessed from the thyroid measurements of adults."
Majia here: notice all the estimations in the article about how calculations for kids were extrapolated. Notice also that exposure is limited to March 15 in this passage:
[Excerpted] "As mentioned earlier, we considered that the rainfall on March 15th resulted in deposition of ambient radioactive materials on the ground and subsequent less possibilities to inhale them. The maximum I-131 activity detected in the thyroid of an adult was 1.5 kBq. Assuming the inhalation exposure took place for 4 hours on the afternoon of March 15th (see above), we estimated that this person could inhale as much as 85 kBq of I-131. Using the thyroid activity and breathing rate16, the maximum atmospheric I-131 concentration was estimated to be 23 kBq m−3. In our data analysis, we did not consider I-132 exposure due to lack of information. " Majia here: It is interesting that even with this set of limitations the article here finds that the children might have been subject to doses on excess of 50 millisieverts:
[Excerpted] "Using the maximum atmospheric concentration, the thyroid dose for different age groups from inhalation of I-131 was calculated for children as shown in Table 2. In this estimation the dose for 1-, 5- and 10-year-old children could exceed 50 mSv. If children in this age range remained in Tsushima District after the radioactive plume arrived in the afternoon of March 15th, they might have experienced further exposure to I-131 Majia here: Yet, the study results indicate an exposure of only 4 millisieverts for kids? How is that? Well, look at this passage from the methodology section. The study is using a lot of estimations in its calculations and one of those estimations is based on the premise that iodine-131 was inhaled only on March 15th
[Excerpted] "Where DT,0 is the thyroid equivalent dose (mSv) assuming that they inhaled I-131 on March 15th, t is the elapsed time between March 15th and the measured date, Teff is the effective half-life of I-13117, f is the equivalent thyroid dose coefficient16, 17, and i is the thyroid uptake factor equal to 0.3. The effective half-lives of 3 months (from 0 to 1 year of age), 5 years (more than 2 to 7 years of age), 15 years (more than 12 to 17 years of age), and adult (more than 17 years of age) were calculated using each biological half-life given by ICRP Publication 6717, and they were estimated to be 4.67, 5.94, 7.15, and 7.27 days, respectively." MAJIA HERE: This research study's conclusions based on 61 subjects, using a methodology that entailed a scintillation spectrometer held to the neck during the period of April 12 to 16th 2011 presuming .3 uptake RAISES MORE QUESTIONS THAN IT ANSWERS.
[Excerpted] We measured activity in the thyroid during the period from April 12th to 16th, 2011, using a 3-inch × 3-inch NaI(Tl) scintillation spectrometer (JSM-112, Hitachi Aloka Medical, Ltd., Tokyo). We wrapped the detection head with plastic foil and cleaned the neck with alcohol wipes so as to avoid radioactive contamination. We then placed the detection head on the cleaned part of the neck and started the measurement.
MAJIA HERE: I cannot comment on whether a scintillation spectrometer held to the neck is a reliable indicator of iodine-131 uptake.
But I can suggest that the sample size was not adequate and the assumptions about the time and amount of uptake raise many more questions than they answer.
Majia Here: I am not saying that this data set is the truth as contrasted with the comparatively low level of exposure extrapolated from the study published at Nature.
What I am saying is that there were quite a few accounts published in the Japanese news media that children in Fukushima have thyroid nodules and this development is very worrying.
Given efforts to trivialize the disaster, I hope to raise questions about the adequacy of the Nature study in predicting Fukushima children's exposure to iodine-131.
The release of iodine 131 was not restricted to March 15 2011.
On July 6 2011 the Japanese press Kyodo reported that in a March survey of 1,080 children aged 0 to 15 in Iwaki, Kawamata, and Iitate, 45% of kids in Fukushima survey had thyroid exposure to radiation[i] In August, NHK reported that Japan’s nuclear commission had erased children’s exposure data derived from a test of 1,000 children aged 15 or younger who had been screened for radiation affecting their thyroid.[ii]The report stated that one four year old child had a thyroid exposure of 35 millisieverts, but that the amount was “not considered a health threat.” This exposure level accounts only for Iodine-131 and does not incorporate the child’s total exposure to other radionuclides. In April 2012, the Peace Philosophy Centre posted the results of the Fukushima government’s March 2012 survey of 38,001 children under 18 located in thirteen Fukushima prefecture cities. Thyroid nodules (5.0mm) or cyst (20.0mm) were detected in 13,460 individuals, or 35.3% of the sample. These results were an increase of 5.6% from a January pre-test.[iii]
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