Cesium rich microparticles

The Discovery of Cesium Rich Microparticles

The 2011 Fukushima nuclear disaster was the second-most serious nuclear accident in history, after Chernobyl in 1986. It caused serious damage to the nuclear reactors 1, 2, 3 and 4 at the Fukushima Daiichi Nuclear Power Plant. As a result, massive amounts of radionuclides were released in Fukushima prefecture, posing serious environmental threats of known, and unknown, nature.

The initial nuclear accident led to the release of several radioactive isotopes, including iodine-131, cesium-134 and cesium-137. Caesium 137 is one of the main sources of radioactive contamination after any nuclear reactor accident. In Fukushima accident too, Cs 137 is chiefly responsible for almost all the radioactivity in the contaminated regions. It is because it has a relatively long half-life of 30.15 years. This means it can last a long time in the ecosystem; for up to 300 years. High concentrations of Cs-137 are commonly found in meat, dairy, mushrooms, berries and game.

Cs 137 mimics potassium. By this mechanism it can easily enter into the muscle tissue, including the heart. It can cause severe damage to the heart through various mechanisms. Now seven and a half years later, it has been discovered that besides Cs 137 and I-131, another type of Cs was also released.

A different form of Cs, Cs-rich microparticles (CsMPs), has been found in the soils near the plant. These microparticles are condensed matter that was formed within the reactors during the disastrous meltdown, and thus hold important clues regarding the state of the radioactive material inside the reactors. This information can be an extremely useful tool in carrying out the decommissioning process, which has seen many roadblocks due to the lack of such information.

So, what are these microparticles? And what kinds of health risks do they carry? Let’s find out.

Caesium-rich micro-particles (CsMPs)
Initially it was believed that during the meltdowns, damaged reactors released only volatile, gaseous radionuclides, such as caesium and iodine. However, very small radioactive particles were also released into the environment.

These highly radioactive cesium-rich microparticles (CsMPs) were released at an early stage of the 2011 nuclear disaster. In fact, these caesium-bearing particles were first found some 170 km southwest of the Fukushima nuclear power plant. [1] [2]

The nanoparticles are primarily made of glass, and contain large amounts of radioactive caesium, along with trace amounts of uranium and technetium. Being small and sparingly soluble, these particles can be easily inhaled and present long-term risks to your health. However, it is not entirely clear how much of these nanoparticles are actually deposited in the soils and sediments. Their impact of the environment is also not clear.

Recently, a team of scientists from Kyushu University of Japan and The University of Manchester, UK, set out to determine the quantity of these CsMPs released into the environment. The scientists used a new method to identify and quantity the contamination. This technique allowed them to count the number of CsMPs in Fukushima soils and also measure the amount of radioactivity linked to these micro-particles.

What did the research say?

The scientists took samples from rice paddy soil from different locations within Fukushima prefecture, ranging from 4 km to 40 km from the reactors. All the samples were found to contain caesium-rich micro-particles with much higher amounts of cesium than thought to be present. The research also found that this form of caesium is different than other forms of Cs that are soluble.

Dr Satoshi Utsunomiya from Japan, also the lead author of the study says, “when we first started to find caesium-rich micro-particles in Fukushima soil samples, we thought they would turn out to be relatively rare. Now, using this method, we find there are lots of caesium-rich microparticles in exclusion zone soils and also in the soils collected from outside of the exclusion zone“. [3]

This method will enable scientists to measure the quantity of caesium-rich micro-particles in other areas of Fukushima prefecture as well as the amount of radioactivity contributed by the contributed by the CsMPs in contaminated soils.

In a previous study, the researchers found Uranium and other radioactive materials in tiny particles that had been released during the nuclear accident. [4] The particles were found to be five micrometres or less. This is nearly 20 times smaller than the width of a human hair. The study showed that the fragments of debris from the damaged reactors were found inside the exclusion zone, in paddy soils collected 4 km from the nuclear disaster.

Dr Gareth Law from Manchester and an author on the paper, says: “Our research strongly suggests there is a need for further detailed investigation on Fukushima fuel debris, inside, and potentially outside the nuclear exclusion zone. Whilst it is extremely difficult to get samples from such an inhospitable environment, further work will enhance our understanding of the long-term behaviour of the fuel debris nano-particles and their impact.” [5]

Health concern?

In one soil sample, the cesium micro particles was found to contribute as much as 32% of the total radioactivity in the soil. These findings show that total radioactivity increased with increasing numbers of CsMPS. This proves that, while there have been claims that most parts of Fukushima had low dose radioactivity, it is wrong to make assumptions without carrying out tests.

The CsMPs are extremely small and are associated with an extremely high level of radioactivity. CsMPs can trigger the production of high concentrations of hydroxyl radicals. Both these factors pose significant health concern. In addition, CsMPs are now viewed as important transporters that help other radionuclides, such as Uranium, reach the environment. It would be an understatement to say that Uranium, with its half-life of about 4.5 billion years, can remain in the environment for an exceptionally long time. This has only one implication: the impact of the nuclear fallout from the 2011 disaster could last much longer and pose much more serious health concerns than previously imagined.

While not much is known about the health impact of caesium rich microparticles, the study reported that it is highly likely that these radioactive particles can be lodged very deep in the respiratory system.

What does this discovery mean for the decommissioning process?

One of the most challenging issues remains the decommissioning of four nuclear reactors that were damaged during the accident. There is much uncertainty around the conditions inside the reactors. There is no firm information regarding the state, and the physical and chemical properties of the debris, which is composed of melted fuel rods and the components of damaged reactors. Unknown conditions, high temperatures and unknown level of radioactivity prevent access, thus delaying the decommissioning efforts.

It is, therefore, important to get more insights into the physical and chemical state of the radionuclides inside the reactors so the decommission process can be successfully carried out. That is where the detailed study of CsMPs can be useful, as these particles offer significant clues about so many things; for example, the nature of the debris, conditions within the reactors and status of the melted fuel rods. More specifically, characteristics and isotopic fingerprints of these CsMPs give important clues for understanding the nature of the chemical reactions that took place during meltdown of the reactors. This kind of information is likely to smooth and hasten the decommissioning process undertaken by TEPCO.

Other surprising sources of Cs radioactivity

Years after the Fukushima disaster, more radioactive particles have been found in the sand and in brackish ground water underneath the surrounding (and not so close) beaches. [6] Surprisingly, the scientists found the highest Cs 137 levels not in the ocean, rivers or portable groundwater but in the groundwater beneath beaches up to, and over tens of kilometres away from the Fukushima power plant.

The researchers explained that some of the radioactive cesium – carried along the coast after the initial disaster – stuck to the sands on the beach. What is interesting to note is that caesium loosens up from the sand in the presence of salty water. And when new waves bring along salty seawater and the brackish ground water becomes salty, the sand sheds the radioactive cesium into the ocean water. These findings are critical, considering that half of the world’s 440 nuclear power stations are located along coastlines!

In fact, in 2016 another study highlighted that the glassy Cs 137 microparticles landed as far as Tokyo just few days after the nuclear accident in 2011. The analysis showed that these particles consisted of high amounts of Cs along with Fe-Zn-oxides nanoparticles. This content was embedded in glass that was formed when the molten core interacted with concrete inside the reactors. Further analysis showed that substantial amount of the radioactivity came from tiny glass particles containing radioactive cesium, and not from the soluble form of Cs 137. [7]

What does this new discovery mean?

All these observations, especially the recent discovery of a widespread presence of a new type of radioactive particles questions many assumptions about the prevailing radioactivity around Fukushima. The microscopic glass particles are so tiny that they can float in air and be inhaled. In spite of the size, CsMPs generally have a high level of radioactivity.

Discovery of the CsMPS as a radiation dispersal pathway has largely been ignored. This report clearly suggests that CsMPS may have been a major way in which radioactivity spread to far flung areas. Additionally, it raises questions of just how much radiation is present in areas assumed to be safe.

Previously, it was reported that radioactive materials from the Fukushima Daiichi nuclear power plant disaster had been detected in the offshore areas around Vancouver, Canada. The radioactive materials were reported to be cesium-134 and cesium-137. Further testing showed that there was more cesium-137 than cesium-134. The concentration of these radioactive cesium isotopes was reportedly lower than the Canadian safe limit for cesium in drinking water. And apparently, these levels don’t present any real-time danger to human health.

Now, cesium-134 has a short half-life of two years. This is much shorter than the 30 years for cesium-137. This means that while the radioactivity of cesium-134 quickly comes down by half in two years, that of cesium-137 takes 30 years. In other words, with increased quantities of cesium-137, the low-dose radiation will stick around for a very long time.

That radioactive material could be found as far away from Fukushima as Vancouver in Canada is reason to worry. Presence of radioactive material in far-flung areas can be explained using the new discovery of cesium encapsulated in glass particles.

Conclusion

This new research suggests that there is a more serious danger lurking in the soil. The fact that this came to light only recently shows just how little is known about low dose radioactivity and its effects on human health and the environment. While the world has used nuclear power for decades, we simply do not understand it well enough.

Specifically, the dangers of low radiation are poorly understood. Most experts in this field believe that exposure to even a small amount of radiation can have significant effects over time.

It has been known for a long time that ionizing radiation pulls out electrons from cellular structures such as DNA, mitochondria, proteins, lipids and membranes. This increases the risk of developing cancer and many other non-cancer conditions. It has also been known that the higher the accumulated doses of radiation, the higher the risk to health. But, no conclusive studies have previously been done on the effects of low level radiation.
However, recent studies have changed this perception about the risks associated with chronic, low-dose radiation exposure. A 2015 study showed “a positive association between cumulative dose of ionising radiation and death caused by leukaemia among adults who were typically exposed to low doses.” [8]

A study as recent as 2017 found that exposure to low-doses of ionising radiation increases the risk of cardiovascular damage. This risk has been observed up to decades after the exposure. [9] The researchers emphasized that that even small doses, as small as 0.5 Gy, could have a negative impact. How small is this dose? You can get exposed to this amount of radiation after repeated CT scans.

Going by these new studies and reports, it is quite obvious that there are many facts about radioactive contamination and their hazardous consequences that are still unknown and unpredictable. And going by the relatively high radioactivity in the CsMPs, it is probable that the amount of radioactivity around Fukushima and beyond could be much higher than previously assumed.

References:

1. Adachi et al. Emission of spherical cesium-bearing particles from an early stage of the Fukushima nuclear accident. Sci. Rep. 3, 2554/1–5 (2013).
2. Abe et al. Detection of uranium and chemical state analysis of individual radioactive microparticles emitted from the Fukushima nuclear accident using multiple synchrotron radiation X-ray analyses. Anal. Chem. 86, 8521–8525 (2014).
3. University of Manchester. Fukushima Radioactive Particle Release Was Significant, Says New Research. Lab Manager. 2018.
4. Ochiai et al. Uranium Dioxides and Debris Fragments Released to the Environment with Cesium-Rich Microparticles from the Fukushima Daiichi Nuclear Power Plant. Environmental Science & Technology. 2018.
5. Manchester University. “New evidence of nuclear fuel releases found at Fukushima.” ScienceDaily. 2018
6. Sanial et al. Unexpected source of Fukushima-derived radiocesium to the coastal ocean of Japan. PNAS. 2017.
7. Radioactive cesium fallout on Tokyo from Fukushima concentrated in glass microparticles. Phys.org. 2016.
8. Leurad et al. Ionising radiation and risk of death from leukaemia and lymphoma in radiation-monitored workers (INWORKS): an international cohort study. The Lancet. Haemotology.
9. Azimzadeh et al. Proteome analysis of irradiated endothelial cells reveals persistent alteration in protein degradation and the RhoGDI and NO signalling pathways. Internation Journal of Radiation Biology. 2017