Study: Radioactive Hot Particles Still Afloat Throughout Japan Six Year After Fukushima Meltdowns

Radioactive particles of uranium, thorium, radium, cesium, strontium, polonium, tellurium and americium are still afloat throughout Northern Japan more than six years after a tsunami slammed into the Fukushima Daiichi Power Plant causing three full-blown nuclear meltdowns. That was the conclusion reached by two of the world’s leading radiation experts after conducting an extensive five-year monitoring project.

Arnie Gundersen and Marco Kaltofen authored the peer reviewed study titled, Radioactively-hot particles detected in dusts and soils from Northern Japan by combination of gamma spectrometry, autoradiography, and SEM/EDS analysis and implications in radiation risk assessment, published July 27, 2017, in Science of the Total Environment (STOLEN).

Gundersen represents Fairewinds Associates and is a nuclear engineer, former power plant operator and industry executive, turned whistleblower, and was CNN’s play-by-play on-air expert during the 2011 meltdowns. Kaltofen, of the Worcester Polytechnic Institute (WPI), is a licensed civil engineer and is renowned as a leading experts on radioactive contamination in the environment.

415 samples of “dust and surface soil” were “analyzed sequentially by gamma spectrometry, autoradiography, and scanning electron microscopy with energy dispersive X-ray analysis” between 2011 and 2016. 180 of the samples came from Japan while another 235 were taken from the United States and Canada. The study further clarifies, “Of these 180 Japanese particulate matter samples, 57 were automobile or home air filters, 59 were surface dust samples, 29 were street dusts (accumulated surface soils and dusts) and 33 were vacuum cleaner bag or other dust samples.”

108 of the Japanese samples were taken in 2016, while the other 72 were gathered in 2011 after the meltdowns. Gundersen and Kaltofen tapped 15 volunteer scientists to help collect the dust and soil — mostly from Fukushima Prefecture and Minamisouma City. “A majority of these samples were collected from locations in decontaminated zones cleared for habitation by the National Government of Japan,” the study revealed. For the 108 samples taken in 2016, an “International Medcom Inspector Alert surface contamination monitor (radiation survey meter) was used to identify samples from within low lying areas and on contaminated outdoor surfaces.”

A Fairewinds Associates’ video from 2012 features Gundersen collecting five samples of surface soil from random places throughout Tokyo — places including a sidewalk crack, a rooftop garden, and a previously decontaminated children’s playground. The samples were bagged, declared through Customs, and brought back to the U.S. for testing. All five samples were so radioactive that according to Gundersen, they “qualified as radioactive waste here in the United States and would have to be sent to Texas to be disposed of.” Those five examples were not included as part of the recently released study, but Gundersen went back to Tokyo for samples in 2016. Those samples were included, and were radioactive, and according to Gundersen were “similar to what I found in Tokyo in [2012].”


Furthermore, 142 of the 180 samples (about 80 percent) contained cesium 134 and cesium 137. Cesium 134 and 137, two of the most widespread byproducts of the nuclear fission process from uranium-fueled reactors, are released in large quantities in nuclear accidents. Cesium emits intense beta radiation as it decays away to other isotopes, and is very dangerous if ingested or inhaled. On a mildly positive note, the study shows that only four of the 235 dust samples tested in the United States and Canada had detectable levels of cesium from Fukushima.

Cesium, due to its molecular structure, mimics potassium once inside the body, and is often transported to the heart where it can become lodged, thereafter mutating and burning heart tissue which can lead to cardiovascular disease. Other isotopes imitate nutritive substances once inside the body as well. Strontium 90 for example mimics calcium, and is absorbed by bones and teeth.

“Different parts of the human body (nerves, bones, stomach, lung) are impacted differently,” Kaltofen told EnviroNews in an email. “Different cells have radio-sensitivities that vary over many orders of magnitude. The body reacts differently to the same dose received over a short time or a long time; the same as acute or chronic doses in chemical toxicity.”

In contrast to external X-rays, gamma, beta or alpha rays, hot particles are small mobile pieces of radioactive elements that can be breathed in, drunk or eaten in food. The fragments can then become lodged in bodily tissue where they will emanate high-intensity ionizing radiation for months or years, damaging and twisting cells, potentially causing myriad diseases and cancer. The study points out, “Contaminated environmental dusts can accumulate in indoor spaces, potentially causing radiation exposures to humans via inhalation, dermal contact, and ingestion.”

The study also explains, “Given the wide variability in hot particle sizes, activities, and occurrence; some individuals may experience a hot particle dose that is higher or lower than the dose calculated by using averaged environmental data.” For example, a person living in a contaminated area might use a leaf blower or sweep a floor containing a hefty amount of hot particle-laden dust and receive a large does in a short time, whereas other people in the same area, exposed to the same background radiation and environmental averages, may not take as heavy a hit as the housekeeper that sweeps floors for a living. People exposed to more dust on the job, or who simply have bad luck and haphazardly breathe in hot radioactive dust, are at an increased risk for cancer and disease. High winds can also randomly pick up radioactive surface soil, rendering it airborne and endangering any unsuspecting subject unlucky enough to breath it in.

Hot particles, or “internal particle emitters” as they are sometimes called, also carry unique epidemiological risks as compared to a chest X-ray by contrast. The dangers from radiation are calculated by the dose a subject receives, but the manner in which that dose is received can also play a critical factor in the amount of damage to a person’s health.

“Comparing external radiation to hot particles inside the body is an inappropriate analogy,” Gundersen told EnviroNews in an email. “Hot particles deliver a lot of energy to a very localized group of cells that surround them and can therefore cause significant localized cell damage. External radiation is diffuse. For example, the weight from a stiletto high heal shoe is the same as the weight while wearing loafers, but the high heal is damaging because its force is localized.”

Kaltofen elaborated with an analogy of his own in a followup email with EnviroNews saying:

Dose is the amount of energy in joules absorbed by tissue. Imagine Fred with a one joule gamma dose to the whole body from living in a dentist’s office over a lifetime, versus Rhonda with exactly the same dose as alpha absorbed by the lung from a hot particle. Standard health physics theory says that Fred will almost certainly be fine, but Rhonda has about a 10 percent chance of dying from lung cancer — even though the doses are the same.

External radiation and internal hot particles both follow exactly the same health physics rules, even though they cause different kinds of biological damage. Our data simply shows that you can’t understand radiation risk without measuring both.

Some isotopes, like plutonium, only pose danger to an organism inside the body. As an alpha emitter, plutonium’s rays are blocked by the skin and not strong enough to penetrate deep into bodily tissue. However, when inhaled or ingested, plutonium’s ionizing alpha rays twist and shred cells, making it one of the most carcinogenic and mutagenic substances on the planet.

“Measuring radioactive dust exposures can be like sitting by a fireplace,” Dr. Kaltofen explained in a press release. “Near the fire you get a little warm, but once in a while the fire throws off a spark that can actually burn you.”

“We weren’t trying to see just somebody’s theoretical average result,” Kaltofen continued in the press release. “We looked at how people actually encounter radioactive dust in their real lives. [By] combining microanalytical methods with traditional health physics models… we found that some people were breathing or ingesting enough radioactive dust to have a real increase in their risk of suffering a future health problem. This was especially true of children and younger people, who inhale or ingest proportionately more dust than adults.”

“Individuals in the contaminated zone, and potentially well outside of the mapped contaminated zone, may receive a dose that is higher than the mean dose calculated from average environmental data, due to inhalation or ingestion of radioactively-hot dust and soil particles,” the study says in summation. “Accurate radiation risk assessments therefore require data for hot particle exposure as well as for exposure to more uniform environmental radioactivity levels.”

Radioactively-hot Particles Detected in Dusts and Soils from Northern Japan by Combination of Gamma Spectrometry, Autoradiography, and SEM/EDS Analysis and Implications in Radiation Risk Assessment


Dr. Marco Kaltofen – Nuclear Science and Engineering Program, Dept. of Physics, Worcester Polytechnic Institute

Arnie Gundersen – Chief Engineer, Fairewinds Energy Education, Community Research Fellow University of Vermont 

Complete Methodology: 

The purposes of the study were to identify and collect samples with a high potential to contain radioactively-hot particles for microscopic examination, to determine if local hot spots of contamination existed at the time of the Fukushima Dai-ichi meltdowns, and finally to document whether any hot spots persisted five years after the accidents.

Samples of 180 Japanese house dusts, car engine filters, HVAC filters, street dusts and fine surface soils were collected and shipped to Worcester Polytechnic Institute for radioisotope analysis. A total of 235 US and Canadian samples of similar matrices were collected between 2011 and 2015. Of these 180 Japanese particulate matter samples, 57 were automobile or home air filters, 59 were surface dust samples, 29 were street dusts (accumulated surface soils and dusts) and 33 were vacuum cleaner bag or other dust samples. All filters were in service on or after March 11, 2011, the date of the initial releases from the Fukushima Dai-ichi reactors.

Of the 180 samples from Japan, 108 were collected in Japan during 2016 while the remaining 72 samples were collected during 2011. These samples included fine surface soils, sediments from drainage areas, and soils from floor mats. Dusts were collected from bulk and surface dust accumulations; including air handling fans, residential air filters, vacuum cleaner bags, automobile air filters, public restroom ventilation fans and from surfaces at public transportation points throughout northern Japan. This study used a mix of samples submitted by volunteers and by the authors. There were controls on the volunteers’ methods used to select samples, however direct sampling oversight was limited. Fifteen scientists and volunteer citizen-scientists collected these samples in areas across Japan, but predominantly in Fukushima Prefecture and Minamisoma City. Sampling locations were in publicly-accessible areas such as bike paths, roadways, sidewalks and public buildings. Permits were received to sample in restricted areas where post-Fukushima meltdown decontamination work was in progress. A majority of these samples were collected from locations in decontaminated zones cleared for habitation by the National Government of Japan.

Sample collection

Sample collection was biased by performing a preliminary visual survey to facilitate collection from areas where fine particulate matter can accumulate, such as low spots on roads or rooftops, air handling fan blades, floor mats and rooftops. For the 2016 sample set (108 of 180 samples), an International Medcom Inspector Alert surface contamination monitor (radiation survey meter) was used to identify samples from within low lying areas and on contaminated outdoor surfaces. Screening introduces a bias to the soil sample set allowing for maximum probability of collecting particulate matter that might contain hot particles. Indoor dusts, HVAC system dusts and auto air filters were randomly selected and no survey meters were used nor were surface radiation measurements taken prior to dust sample collection.

At the time of the 2016 sampling campaign, mapped surface activity data was available from Safecast, an open citizen-led group that collected activity data via a standardized device of their own design, the bGeigie. Uncontaminated areas in Japan (as mapped by have bGeigie-measured activities on the order of 0.08 uSv/hr. or less. Areas of known contamination are on the order of 0.16 uSv/hr. and higher. More than 90 percent of the samples in this study come from the areas Safecast-mapped as 0.16 uSv/hr. and higher (Figure 1). This indicates that the data are more representative of the contaminated zone, rather than of Japan as a whole. Mapping via the Safecast bGeigie proceeds with a plastic alpha and beta shield around the detector element. This makes the device essentially a gamma activity monitor. Thirteen of the 2016 samples from Japan were measured by the primary instrument (Ortec NaI well gamma photon detector) and the bGeigie. With the shield present on the bGeigie so that both devices measured gamma energy only, the R2 value between the two sets was 0.97, a good fit (Figure 2). Without the shield the bGeigie also accumulated beta and alpha energy, so the fit was poorer, with R2 = 0.15. The strong correlation between the bGeigie in gamma mode and the Ortec spectrometer is added evidence that the sampling methodology provides data that is more representative of the contaminated areas in northern Japan, and less so for Japan as a whole.

For each 2016 sample collection location point, a photograph was taken to provide an image of where the sample was collected as well as a record of the GPS location. All Japanese samples were air dried at ambient temperature prior to analysis, then shipped internationally to Worcester Polytechnic Institute in Worcester, MA, USA, for analysis.

Motor vehicle engine air filters process large volumes of air. In Japan private vehicles average 65 liters of gasoline use per month. (Schipper 2009) This fuel requires approximately 638 cubic meters of air for complete combustion. This is about 30 cubic meters per day, which is in the same order of magnitude as a working adult tidal air volume of 10 to 20 cubic meters per day. It was hypothesized that engine air filters in routine use and first installed prior to March 11, 2011 would provide an approximation of the amount of radioactive dusts present in ambient air for each driving region.

Bulk dust and street dust/soil samples were air dried at ambient temperatures prior to analyses. Dust samples containing macroscopic objects and excessive pet hair were sieved to pass a 150 micron brass ASTM #100 screen. Samples were divided and separately screened by gamma spectroscopy to determine if activity was heterogeneously distributed within samples. Samples were sequentially divided if necessary, based on gamma-screening results.

Dust was mechanically removed from automobile and HVAC filters. Motor vehicle air filters varied in usage from nearly new to as much as 55,000 logged kilometers of use. Sample results for dust samples were reported on a kBq kg-1 basis. Eight filter samples with detectable activities but with dust that could not be quantitatively removed from filter media were assigned a dust mass of 1.0 g. This introduced a low bias to these samples. Nine samples had activities greater than 0.25 MBq kg-1. To ensure safe transport, these samples were mass-limited to 3 grams before shipping from Japan.

Included in this set of nine atypically-radioactive samples, was a 300 mg sample of street dust received from a location about 10 km from the Fukushima-Dai-ichi accident site in Namie-machi, Futaba-gun, Fukushima Prefecture. This is in the restricted zone, close to but just outside of the exclusion zone. A very similar sample was collected from Iitate. The particulate matter samples were analyzed by sodium iodide gamma spectrometry. One vacuum bag received from a home in Nagoya, Japan, yielded subsamples with no detectable radioactivity above background, despite a sizable amount of activity for the bag as a whole. (Nagoya is 433 km from Fukushima Dai-ichi). By sample division and hot particle isolation with a pancake detector, a single 1 cm by 2 cm glass slide was prepared, with a small number of microscopic dust particles (with activity > 1 MBq ug-1) mounted via double sided adhesive tape.

Analyses of the samples proceeded sequentially by NaI gamma spectrometry, autoradiography of high activity samples, and scanning electron microscopy / energy dispersive X-ray analysis (SEM/EDS) of individual radioactively-hot particles identified by autoradiography (Moody 2015). Autoradiographs were prepared from the highest specific activity samples using blue-sensitive X-ray film, followed by SEM/EDS analysis of autoradiographically positive portions of the sample. Air filter media that had positive gamma spectrometry results were mounted in a single layer onto double sided adhesive paper sheets. These sheets with dusts were then attached to 3 mm thick copper plates. Vehicle and HVAC air filters were prepared by cutting the filter media from their frames, and mounting the filter media on 3 mm thick copper plates. A sheet of blue-sensitive Xray film was sandwiched with the mounted filters, and exposed in a dark photographer’s box for seven days. The autoradiographs used MidSci® classic blue autoradiography film BX and D76 processing.

All gamma spectrometry data are corrected for geometry, and were standardized against a known activity of 137Cs. Gamma photon analyses used Ortec® NaI and Canberra® GeLi flat plate photon detectors. An Ortec® NaI well detector and 1K MCA were also used. Counting efficiency @ 662 keV was found to be 30% based on use of a certified calibration standard from an Eckert & Ziegler Isotope Products standard source, manufactured and certified on Sept. 12, 2011, with 40.12 nCi of 137Cs. The 137Cs in the standard used for quantitation and any Fukushima-related 137Cs in the samples were of the same approximate age, therefore no 137Cs decay correction is warranted in this five-year study. Nuclides not amenable to gamma spectrometry, such as strontium, were not analyzed in this study.

Samples with evident gamma spectral peaks for uranium, thorium or plutonium were selected for SEM/EDS analyses. All particles were mounted as a monolayer on a 25 mm OD Ted Pella, Inc., PELCO® tape tab-covered aluminum SEM stub. If necessary to improve particle conductivity, the samples were carbon or gold coated prior to SEM/EDS analysis. SEM/EDS work was tested commercially at Microvision Laboratories of Chelmsford, MA, using a Bruker® X-Flash® Peltier-cooled silicon drift detector (SDD). The electron beam current was 0.60 nAmperes, accelerated at a voltage of < 0.5 to 60 keV.

Want to look at the numbers? Click below to download the complete data sheet of our samples (.xlsx). 

Activities as radio-cesium

27 july 2017.png


Maps of Safecast data and sample sites in Japan

july 27 2017 2.jpg(Above-left) Safecast map with dark blues representing low contamination

(Above-right) Map of study sample areas using same Safecast color scheme

Boat tracks and other clutter have been removed from this graphic.

Japan Radiation Interactive Map

(Above) Browse the location, supplementary info and photographs of samples taken in Japan with our interactive sample map created by Ben Shulman-Reed, Fairewinds Energy Education program researcher. 

Safecast bGeigie data vs. Ortec NaI gamma spectroscopy data


Japanese dusts and sediments presented by specific activity in kBq kg-1

27 july 2017 3.jpg


Distribution of total radiocesium activities in particulate matter samples from Japan

27 july 2017 4.jpg


Gamma spec Ibaraki Prefecture, analyzed April 11, 2011



Tokyo vehicle air filter image (Left) and 7 day exposure autoradiograph (Right) Corresponding auto exposed points on the X-ray film are connected by red lines.

27 july 2017 5.jpg


SEM image of hot particle, magnification 5000 X.

27 july 2017 6


(Top) SEM/EDS spectrum showing one nodule of hot particle with 15.6% Cs, 16.7% Te, 1.2% Rb, 0.61% Po.  (Bottom) second nodule with 48% Te, 1.2% Po, 0.18% Dy (analyzed 12/18/2013).

27 july 2017 7



To read more at :

Increases in perinatal mortality in prefectures contaminated by the Fukushima nuclear power plant accident in Japan: A spatially stratified longitudinal study.

“Radiation damage spreading to Fukushima and other Tohoku Prefectures, and Kanto Prefectures Tokyo, Saitama, Chiba, is demonstrated. Perinatal mortality is increasing, it has been announced for the first time in peer-reviewed medical journals the Fukushima/Perinatal mortality link.”

3 oct 2016 perinatal mortality.jpg



Descriptive observational studies showed upward jumps in secular European perinatal mortality trends after Chernobyl.

The question arises whether the Fukushima nuclear power plant accident entailed similar phenomena in Japan.

For 47 prefectures representing 15.2 million births from 2001 to 2014, the Japanese government provides monthly statistics on 69,171 cases of perinatal death of the fetus or the newborn after 22 weeks of pregnancy to 7 days after birth.

Employing change-point methodology for detecting alterations in longitudinal data, we analyzed time trends in perinatal mortality in the Japanese prefectures stratified by exposure to estimate and test potential increases in perinatal death proportions after Fukushima possibly associated with the earthquake, the tsunami, or the estimated radiation exposure.

Areas with moderate to high levels of radiation were compared with less exposed and unaffected areas, as were highly contaminated areas hit versus untroubled by the earthquake and the tsunami.

Ten months after the earthquake and tsunami and the subsequent nuclear accident, perinatal mortality in 6 severely contaminated prefectures jumped up from January 2012 onward: jump odds ratio 1.156; 95% confidence interval (1.061, 1.259), P-value 0.0009.

There were slight increases in areas with moderate levels of contamination and no increases in the rest of Japan.

In severely contaminated areas, the increases of perinatal mortality 10 months after Fukushima were essentially independent of the numbers of dead and missing due to the earthquake and the tsunami.

Perinatal mortality in areas contaminated with radioactive substances started to increase 10 months after the nuclear accident relative to the prevailing and stable secular downward trend.

These results are consistent with findings in Europe after Chernobyl. Since observational studies as the one presented here may suggest but cannot prove causality because of unknown and uncontrolled factors or confounders, intensified research in various scientific disciplines is urgently needed to better qualify and quantify the association of natural and artificial environmental radiation with detrimental genetic health effects at the population level.




Read more on the PDF:


Majority of municipalities planning residential decontamination haven’t finished work

001People walk along a street in the Miyagi Prefecture town of Yamamoto, where planned decontamination of homes has not yet been carried out. Some residents do not even know that decontamination work is scheduled.

September 22, 2014

More than half of the 74 municipalities in the Tohoku and Kanto regions that have planned decontamination of residences in areas where surveys of radioactive pollution are needed have yet to complete the work, a survey by the Mainichi Shimbun has found.

The survey showed that as of the end of June, 40 cities, towns and villages had yet to complete planned decontamination of homes, with at least 311,700 still needing work. In two municipalities — the Miyagi Prefecture town of Yamamoto and the Fukushima Prefecture town of Shinchi — residential decontamination had not begun at all.

Altogether, 104 municipalities in the eight prefectures of Iwate, Miyagi, Fukushima, Ibaraki, Tochigi, Gunma, Saitama and Chiba have been designated by the environment minister as areas where surveys of radioactive pollution are needed. The Mainichi Shimbun questioned all of these municipalities on the progress of decontamination of houses, roads, farmland and forests, and received replies from all of them. The survey did not cover schools and other public facilities, where decontamination work has mostly been completed.

Of the 104 municipalities, 74 have made plans to decontaminate residents’ homes. Twenty-nine of those that have not yet completed this work are located in Fukushima Prefecture, which has a large number of houses subject to decontamination. At least 286,002 homes in these 29 municipalities still need to be decontaminated. Another four municipalities are located in Tochigi Prefecture, four more in Miyagi Prefecture, two in Ibaraki Prefecture and one in Gunma Prefecture. In these four prefectures, 25,719 residences remain to be cleaned.

When asked how many homes would be decontaminated in the future, three municipalities did not reply. One of them explained that data was still being compiled. The Miyagi Prefecture town of Yamamoto has planned decontamination of 1,495 homes, while the town of Shinchi in Fukushima Prefecture has planned to decontaminate 600 homes, but the work has yet to commence in either of the municipalities.

When questioned why work was not progressing, many municipalities cited a lack of temporary storage areas for radioactive waste.

“We are having extreme difficulty securing places to temporarily store contaminated soil,” a representative of the Fukushima Prefecture city of Iwaki said. The Tochigi Prefecture town of Nasu, meanwhile, stated that the process of gaining consent from the vast number of people involved in properties was taking a long time. Other municipalities reported similar difficulties in gaining consent from landowners.

In addition, five municipalities in Iwate, Ibaraki and Fukushima prefectures said that they had finished decontamination at all of the planned locations, but that there was a need for additional decontamination in spots where relatively high levels of radiation were detected, such as under the eaves of homes.

Commenting on progress, a representative of the Ministry of the Environment said, “Fukushima Prefecture has a lot of homes to deal with, but it is pretty much on pace to complete its projects by the end of fiscal 2015 or 2016. For other prefectures, if you use the number of houses as a base, then about 90 percent is completed.”

Kunihiro Yamada, a professor in environmental studies at Kyoto Seika University, pointed out, “The central government decides on the outline of decontamination methods through guidelines, but leaves the actual task to local bodies, which results in regional differences. There are cases in which hotspots and other problems remain even after the planned work is completed, but the government has yet to present any concrete guidelines for the future.”

A total of 70 municipalities had planned to decontaminate roads, but 41 of them had yet to finish the work. In addition, 28 out of 47 municipalities had yet to complete decontaminating farmland, and 36 out of 44 had yet to decontaminate forests.

Source: Mainichi