A recent letter to JAMA (Journal of the American Medical Assoc). about an ongoing study of human radiation exposures in Minamisoma Japan has caused much misinformation. Sadly, most of the misinformation has been distributed by the news media in the US. The letter is intended to give a glimpse into the study and some of their preliminary discoveries, it is not the final peer reviewed paper. The letter itself gives a number of caveats that have been ignored in media reports. It also does not explain in depth some of the other ongoing factors that cause exposure but are not part of the study or the letter. The media has inaccurately reported the absence of that information in the letter as absence of those factors in the study and on the ground in Japan. That is not the case made by the study authors. The letter’s information about the study does give some useful information but unless that information is taken in the proper context it is quite inaccurate and misrepresents what the authors were presenting.
All Nuclides Not Included:
The study looks at internal contamination by cesium 134 and 137 only. No other radionuclides are included in these body scans. Iodine 131, plutonium, americum, strontium, uranium and a variety of other radioactive contaminants are known to have been released to the environment by Fukushima Daiichi and have been found in food, soil, plant, insect or animal sampling when tested for. The whole body scans only show one narrow slice of the internal exposure spectrum and are not the total of a person’s internal contamination. This narrow testing does not show alpha or beta emitters in the body and does not take into account the varied energy of different isotopes, some with considerably more energy as they decay than others. All of this causes damage inside the body. Iodine 131, a known problematic isotope bombards the thyroid by being taken in by the body and then the thyroid by the same pathways normal dietary iodine would. This isotope & exposure is not included in the study.
Internal vs. External Exposure:
The whole body scans only look at internal exposure. The scans look at cesium trapped inside the body at that specific point in time after being inhaled or ingested. Cesium and other radioactive contamination in the body remain for a period of time and most are shed out of the body gradually. Cesium 137’s biological half life is 70 days. Isotopes like strontium 90 can have a biological half life of up to 18 years. Some of this internal contamination will not go away quickly. Internal contamination of all types is more damaging than external contamination and bombards the body 24/7 where an external source could be shielded, removed or be moved away from.
Most commonly mentioned guidelines for exposure look at external exposure only or a combination of external and internal exposure together to make up the total. The often mentioned ICRP 1 mSv/year rule of thumb takes internal and external sources for a total of all artificial radiation sources the person would be exposed to in a year. These guidelines are over and above any background radiation. Media comparisons to background radiation are erroneous as guidelines look at levels over and above the background radiation. In Minamisoma the environmental air dose radiation levels after the Fukushima Daiichi disaster alone are quite high. The annual external exposure just from fallout in the environment in Minamisoma ranges from 2.5 mSv/year to 10.5 mSv/year. This puts anyone in these areas of Minamisoma over the ICRP limit before any other source of exposure is added in. The internal exposure recorded in the WBC scans would just add to that already unacceptable level. Additional exposure from inhaling or ingesting contaminated dust or other substances would add to the total. Eating contaminated food adds to the total exposure. Environmental external exposure adds to the total.
Scan Is A Picture In Time:
The scans are a picture in time. They show that someone had a certain level of internal cesium exposure on that day. It does not show what their internal cesium exposure looked like months before or what it could look like months later. Other monitoring has indicated internal cesium levels can actually continue to go up rather than down in some cases. ACRO found people with unusually high cesium levels compared to where they lived. Upon further questioning they found people’s diet was almost always the culprit. That they were consuming contaminated food and it was causing cesium to build up in their body. An elderly couple from Minamisoma who were not included in the original study were reported in an Asahi Shimbun article to have levels far higher than the people already tested. The husband had 20,000 bq total body, the wife 10,000 bq total body of combined cesium contamination. The couple ate mostly local produce including local mushrooms, known to be very highly contaminated. The scans found during the earlier time frame do not guarantee an individual person’s internal exposure will go down. Future exposures from various sources are still a problem in the region. The initial trend found in the testing has been that levels have gone down but this appears to be dependent on environment & life habits. One aspect completely lost in the scan data is iodine 131 exposure. Iodine exposure happens quickly and clears the body quickly yet can do considerable damage to the thyroid. Iodine 131 has a biological half life of about 100 days. The iodine exposure not only wasn’t included in the testing, it would have been gone by that time. Residents of Minamisoma may have received a thyroid count of some type by another organization but that data is not matched up to the people scanned for cesium with the WBC scanner. Iodine exposure and cesium exposure could be useful when presented together.
1 mSv Being Misrepresented:
1 mSv/year has been mentioned frequently since the Fukushima disaster as the goal for exposure maximum. This is based off of the IRCP rule of thumb to keep civilian levels of total artificial radiation exposure (both internal and external) to under 1 mSv a year. This would include environmental external exposure, inhaled or ingested internal contamination and any exposure from contaminated food. The current level where food will be taken off the market is 100 bq/kg. This is intended to keep highly contaminated foods out of stores but lower level contaminated foods may still make it to market and not every bit of food is tested. This ICRP rule of thumb was assumed by some in the media to be what was meant by the JAMA letter’s mention of ” Committed effective doses were less than 1 mSv in all but 1 resident (1.07 mSv)“. The letter earlier mentions this: “Common dose-limit recommendations for the public are 1 mSv or less.” This statement was not attempting to compare the committed effective dose number to the ICRP rule of thumb annual exposure number. The statement of committed effective dose being 1 mSv in the letter is not qualified with a time frame. Other Fukushima region body scan studies have used a calculation that expresses the 1 mSv effective dose as being over 50 years for an adult. It is being used as a frame of reference but does not adequately express the total implications of all internal exposure over time inside the body. It does give a uniform reference unit to compare people’s exposures.
The letter also mentions that the committed effective doses did not warrant treatment with prussian blue. Prussian blue treatment is usually suggested for people with considerable acute exposure. It was used to treat acute cases of cesium exposure in Brazil after a number of people came in contact with an unshielded cesium source. The threshold of use is 30 mSv projected committed effective dose, considerably higher than the committed effective doses estimated in Japan. Prussian blue treatment thresholds may not be the best comparison since it appears to be considered more of a treatment for acute exposure. There is one historical instance of people exposed at Chernobyl being treated with prussian blue. A group of Chinese foreign trade entity members were given a whole body scan and found to be within low ranges similar to the lower exposures in Minamisoma. These people were given prussian blue and saw notable improvement in shedding cesium from the body. So there is some precedent for treating people for non-acute cesium contamination at the exposure levels found in Minamisoma.
Exposures Varied Widely:
Individual people’s exposure varied widely. The body readings done in Minamisoma mentioned in the letter ranged from none detected to 10,000 bq. The older couple mentioned in the Asahi article had even larger exposures and are not included in the letter. This seems to be the case found in other testing done. It is a case of radiation roulette. Those who were in the right places or were able to take the right actions at the right time avoided considerable exposure. Those who were in the wrong place on the wrong day or were not able to avoid exposures showed with higher levels. The population in Fukushima was not uniformly exposed. This shows that taking cautionary actions like evacuation, decontamination, staying indoors, restricting certain foods from sale and sourcing safe food from other areas have proven useful in protecting the public.
The JAMA letter’s information is not in a finished form. The final paper should give a wider context and conclusions on the situation. What is known gives a small slice of data to look at. What is known so far from various sources indicates no uniform exposures and that measures to avoid exposure have been quite effective. The US media and the nuclear industry has attempted to use the JAMA letter to claim evacuations of any kind were not needed and people should have been left in the evacuation zone. There have also been claims that the letter proves there were no exposures of significance in Fukushima. Neither is the case as individuals that did not heed evacuation or food safety are now showing up as considerably more exposed than those who were able to take better precautions. Examples such as the individuals in Namie who had much higher thyroid exposure than others and the elderly couple in Minamisoma highlight the importance of evacuations & precautions. This also shows that much additional work is needed to find those with higher exposures and also to monitor those with lower exposures to complete the understanding of their doses vs. outcomes. Follow up on those with lower exposures is also critical to assure their health does not suffer and that any negative outcomes are detected as soon as possible to assure timely treatment. The purpose for this data should not just be understanding the accident but to help those impacted. They should be our first priority.
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