By Francois Diaz-Mauran
Because of the controversy surrounding Satoshi’s paper and the lack of research on the health impacts of these particles, it remains unclear to what extent Tokyo residents have been exposed to dangerous radiation levels as a result of the Fukushima accident.
[…]
Japanese radiochemist Satoshi Utsunomiya found that air samples from March 15, 2011, in Tokyo contained a very high concentration of insoluble cesium microparticles. He immediately realized the implications of the findings for public safety, but his study was kept from publication for years.
On March 14 and 15, 2011—three days after the Great East Japan Earthquake and its resulting tsunami hit the Fukushima nuclear power plant—explosions at two of the plant’s reactor buildings released a huge amount of invisible radioactivity.
[…]
Following the explosions, Japanese researchers rushed to collect and study radioactive materials from the soil and the air to find out what had happened inside the reactors, believed now to have melted down because their cooling systems failed. On March 13, the Tokyo Metropolitan Industrial Technology Research Institute, the agency responsible for measuring the air quality of particulate matter in the Tokyo area, started to collect air samples more frequently. This effort was part of the Tokyo metropolitan government’s emergency monitoring program for environmental radiation, which aimed to detect gamma-emitting nuclides in airborne dust. The filters revealed that at around 10 a.m. on March 15, 2011, a large plume of radioactivity reached Tokyo, some 240 kilometers (149 miles) south of Fukushima. All samples taken on March 14 and March 15 showed spikes in radioactivity.
The institute’s researchers published their first results in the journal of the Japan Radioisotope Association in June 2011 (Nagakawa et al. 2011); they estimated the total exposure dose to humans from radioactive substances, including iodine 131 and cesium 137 found in airborne dust, foodstuffs, and drinking water from the Setagaya ward in the old Tokyo City. Extrapolating from their measurements from March 13 to May 31, they calculated the corresponding annual cumulative dose of radiation in that part of Tokyo as being 425.1 microsieverts, which is less than half the annual dose limit to the public recommended by the International Commission on Radiological Protection. In a second conference publication in English (Nagakawa et al. 2012), the researchers extended their monitoring period to October and estimated that the total annual effective dose due to inhalation for adults in the Tokyo metropolitan area from the Fukushima radioactive plumes was far lower, at 25 microsieverts.
But two years after the accident, Japanese scientists discovered a new type of highly radioactive microparticle in the exclusion zone around the Fukushima plant. The microparticles, which had been ejected from the Fukushima reactors, contained extremely high concentrations of cesium 137—a radioactive element that can cause burns, acute radiation sickness, and even death. Satoshi Utsunomiya, an environmental radiochemist from Kyushu University in southwestern Japan, soon found that these particles were also present in air filter samples collected in Tokyo in the aftermath of the Fukushima accident.
The controversy surrounding his attempts to publish his findings nearly cost him his career and prevented his results from being widely known by the Japanese public ahead of the 2020 Summer Olympics in Tokyo.[1] Scientists still don’t know if these highly radioactive microparticles present significant danger to people, and Satoshi is one of the very few scientists who is focused on trying to find out. “We have the measurements now that tell that the particles did pass over population centers and were being deposited in places,” Gareth Law, a radiochemist from the University of Helsinki, told me. “We should answer the question.”
The discovery
In May 2012, Toshihiko Ohnuki, an accomplished environmental radiochemist then at the Japan Atomic Energy Agency (JAEA), visited Yoshiyasu Nagakawa at the Tokyo Metropolitan Industrial Technology Research Institute, also known as TIRI. Nagakawa was the first author of two TIRI studies on radiation exposure in Tokyo, and Ohnuki asked Nagakawa if he could obtain some air samples for further analysis. Ohnuki had already studied how radioactive cesium fallout from Fukushima reacted with components of contaminated soil. Now, he wanted to do the same with the airborne dust samples from Tokyo.
Nagakawa gave Ohnuki five small filters that had been collected from the Setagaya ward in old Tokyo City at different times on March 15, 2011—the day the radioactive plume reached Tokyo. Ohnuki received the samples without restriction on their use, and no written agreement was made.[2]
Back in his laboratory at JAEA, Ohnuki performed autoradiography of the five samples, revealing many radioactive spots on all of them. The bulk radioactivity on each sample was measured to be between 300 counts per minute for the filter that covered the midnight to 7 a.m. period and 10,500 counts per minute between 10 a.m. and 11 a.m. on March 15.[3] The radiation rate was so high that Ohnuki had to cut some of the filters into small pieces, less than one square centimeter, to keep from saturating the scanning electron microscope. Ohnuki stored the unexamined filters for future analysis.
Months later, in August 2013, four researchers from the Meteorological Research Institute in Japan reported for the first time about a new type of spherical radioactive cesium-bearing particle that had been ejected in the early days of the Fukushima accident (Adachi et al. 2013). The researchers had collected air samples on quartz fiber filters at their institute in Tsukuba, located 170 kilometers southwest of the Fukushima plant. Their findings, published in Scientific Reports, were about to revolutionize the way environmental radiochemists understood the radioactive fallout from Fukushima.
Back in the lab, the researchers placed the filters on an imaging plate and inserted them into a portable radiography scanner. The images revealed many black dots, which indicated the presence of radioactive materials on the filters, with a maximum radioactivity level measured on the sample at 9:10 a.m. on March 15, 2011, four days after the Fukushima accident began. The researchers placed this sample under a scanning electron microscope and then into an energy-dispersive X-ray spectrometer to directly observe the shape and composition of the radioactive materials on the filters.
[…]
Shocking results
The newly discovered entities were initially called spherical cesium-bearing particles, but Satoshi and his co-workers coined the term cesium-rich microparticles, or CsMPs, in 2017, which is now what researchers call them generally (Furuki et al. 2017). CsMPs had not been noted in earlier major reactor accidents.
Scientists knew the microparticles came from the Fukushima reactors because their isotopic ratio between cesium 134 and cesium 137 matched the average ratio for the three damaged reactors calculated by the Oak Ridge National Laboratory.[5] Because these particles emanated from the Fukushima reactors, Satoshi and the other scientists studying them thought that they may contain evidence about reactions that occurred during the accident. But the environmental radiochemist’s curiosity was also triggered by the unique features of these microparticles: Their size is very small, typically two to three microns, even smaller than one micron in some cases.[6] And the cesium concentration in each of the particles is very high relative to their size.
After Satoshi obtained four small pieces of the Tokyo air filters, he designed what he calls “a very simple procedure” to find out whether the filters contained cesium-rich microparticles. In April 2015, he took autoradiograph images of the four pieces, confirming what Ohnuki had already seen with a digital microscope at JAEA. Then Satoshi moved to characterize the structural and chemical properties of the particles using scanning electron microscopy (SEM) and atomic-resolution transmission electron microscopy (TEM). Although the procedure’s design was simple, executing these steps would prove to be extremely difficult.
[…]
Satoshi was now ready to publish his results in a scientific journal. These were important findings that the scientific community needed to know. But Satoshi also understood that they could create a public relations crisis in Japan because his findings contradicted previous statements that played down the implications for public health of Fukushima fallout in Tokyo.
The Goldschmidt Conference—the foremost such international meeting on geochemistry—that year was held in the Japanese city of Yokohama. Satoshi was invited to give a plenary talk and present his research on environmental contamination from the Fukushima disaster (Utsunomiya 2016). During the talk, he presented his new findings on the Tokyo air filters. His talk received a lot of attention and was even reported by several Japanese and international newspapers. After his presentation, the scientific chair of the conference, Hisayoshi Yurimoto, said: “Very interesting results. And also very shocking results.”[1
In April and June 2016, Satoshi conducted dissolution experiments and quickly confirmed that the CsMPs were insoluble in water. The experiments also showed that most of the cesium activity on these filters came from CsMPs. In fact, up to 90 percent of the cesium radioactivity came from these microparticles, not from soluble forms of cesium—meaning that most of the cesium radioactivity detected during the March 15 plume in Tokyo was from CsMPs.
Between 2016 and 2019, a Kafkaesque sequence of events circled about Ohnuki, the former JAEA researcher who gave Satoshi the Tokyo air filter samples, and Satoshi. During that sequence of events, Satoshi’s research paper was accepted for publication by a prestigious scientific journal after peer review—but the journal delayed publication of the paper for years, eventually deciding not to publish it based on mysterious accusations of misconduct that, it turned out, were unwarranted.
As a result, Satoshi’s findings were not made widely known, saving the Japanese authorities a possible public relations crisis as the summer Olympics in Tokyo neared. Because of the controversy surrounding Satoshi’s paper and the lack of research on the health impacts of these particles, it remains unclear to what extent Tokyo residents have been exposed to dangerous radiation levels as a result of the Fukushima accident.
[…]
In October, as Ohnuki dealt with insistent requests that he return the filter samples, Satoshi submitted two research manuscripts to the journal Scientific Reports, one on the first successful isotopic analysis of individual cesium-rich microparticles based on soil samples collected from the exclusion zone at Fukushima, and one on the first characterization of the CsMPs from the Tokyo air filter samples that he had presented during his talk in Yokohama. Both articles were accepted in early January 2017 after peer review.[11]
The Tokyo paper, titled “Caesium fallout in Tokyo on 15th March, 2011 is dominated by highly radioactive, caesium-rich microparticles,” was co-authored by three graduate students from Satoshi’s lab—Jumpei Imoto, Genki Furuki, and Asumi Ochiai, who conducted the experiments—and three Japanese collaborators: Shinya Yamasaki from the University of Tsukuba who contributed to the measurement of samples; Kenji Nanba of Fukushima University, who contributed to the collection of samples; and Toshihiko Ohnuki, who had obtained the samples. The paper included two international collaborators who were world experts in the study of radioactive materials, Bernd Grambow of the French National Center for Scientific Research at the University of Nantes in France and Rodney C. Ewing of Stanford University, who contributed to the research ideas and participated in the analysis of the data. Satoshi was the lead author of the study.
[…]
On the day of the visit, Moriguchi sent an e-mail to Ohnuki, pressing him to inform TIRI about the planned publication. “This type of information makes government agencies very sensitive,” Moriguchi wrote. “If the results obtained from these valuable sample collections conducted at a research institute under the administration were to incur the displeasure of government agencies and it becomes difficult to obtain cooperation from research institutions, we are concerned that this could hinder future research using these types of samples.”
[…]
Almost immediately, Sakurai moved to block the publication, according to e-mails obtained by the Bulletin.
[…]
In July 2017, TIRI increased the pressure by sending a formal complaint to the Tokyo Institute of Technology, where Ohnuki was now employed. In a letter that the researchers were not able to see until a year after it was sent, TIRI accused Ohnuki of “suspected acts violating internal regulations, researcher’s ethics and code of conduct” in providing Satoshi with samples from TIRI without the institute’s consent.
[…]
In June 2019, Satoshi and his co-authors posted their paper on arXiv (Utsunomiya et al. 2019), thereby making the findings public—two-and-a-half years after its acceptance by Scientific Reports.
[…]
The Most Revolutionary Act 