Radiation Exposure and Tohoku Earthquake in Japan

On March 11, 2001, an earthquake with a magnitude of 9.0 on the Richter scale hit Tohoku, Japan, the biggest earthquake in the history of the country. Along with over 15,000 deaths, the earthquake and the subsequent tsunami caused significant damage to the Fukushima Daiichi Nuclear plants (Oskin, 2017). The radiation leaks from the damaged plants led to the immediate evacuation of residents within 20 km of the area and those within 20-30 km were highly suggested to stay inside or evacuate as soon as possible (Zare & Afrouz, 2012).

It was also thought that there was substantial radioactive deposits in the Pacific Ocean. This accident was classified as a Level 7 in the International Nuclear Event Scale, which is defined by a significant release of radioactivity and widespread negative health outcomes for the people in the surrounding area. The only other event that has been classified as a Level 7 is the Chernobyl Power Plant explosion in 1986, demonstrating the devastating magnitude of this accident (Mahr, 2011). The biggest hazard from this nuclear accident was radiation exposure, specifically iodine being the most prevalent. Increased exposure to radioactive iodine is particularly dangerous because it is in known to increase the risk of thyroid cancer (Drew, Swirsky, & Tarrago, 2002). The biggest stakeholders from this accident were the residents that were in the surrounding area. The people who were closest to the power plants had the most amount of radiation exposure, especially the young children. Furthermore, the accident had an effect on the whole Japanese population due to the risk that sources of food were contaminated from the radioactive meltdown. The Tokyo Electric Power Company (TEPCO), the owner of the Daiichi nuclear plants, was responsible for minimizing the spread of radioactivity from the power plants.

        The source of the radioactivity leak resulted from the tsunami's pressure disabling the cooling devices of the nuclear reactors. The generators were then unable to cool down, leading to nuclear meltdowns and a substantial amount of being radioactivity released (Mimura, Yasuhara, Kawagoe, Yokoki, & Kazama, 2011). The most common way people were exposed to the radioactive particles was through inhalation. The amount of radioactive iodine inhalation was dependent on how long the residents in the surrounding area were exposed to outside air and the intensity of the activities they were performing outside (Akiba, 2012). The other major pathway for the radioactive iodine is through ingestion. Ingestion of food from an area with high levels of radioactivity can be a major route of exposure. Specifically, looking at milk and dairy intake is crucial because that is the primary source of thyroid ingestion, especially for children (Steinhauser, Ch?- vez-Ortega, & Vahlbruch, 2017). Other sources of ingestion can include drinking tap water and consuming fish, such as contaminated tuna (Fisher et al., 2013). This contamination could potentially affect the whole Japanese population because fish is such a crucial component of their diet.

        The populations that were most vulnerable to the exposure were the residents living closest to the nuclear plant and children. The people closest to the powerplant would naturally have the highest dose of exposure through inhalation. Even though the people within 20km did evacuate, they were still initially exposed to the nuclear meltdown. Children are also more vulnerable than adults because they have a lower body weight, so the proportion of exposure in their body is higher. When measured, newborns had 16 times higher dose of iodine in their body than adults even when they were exposed to the same amount of radioactive iodine (Drew, Swirsky, & Tarrago, 2002). Children are also more vulnerable because their body and brain are still developing.

        According to the International Commission on Radiological Protection, the reference level of radiation exposure is 500-1000 mSv for those who were working at the site of the nuclear power plant meltdown without it having detrimental effects (Hasegawa et al., 2015). Specifically for thyroid radiation, there is increased risk of thyroid cancer at exposure doses above 100 mSv (Yamashita, Suzuki, Suzuki, Shimura, & Saenko, 2018). Sievert (Sv) is the SI unit for the equivalent radiation dose that equals 1 J/kg (Baes, n.d.). Another commonly used unit is Gray (Gy) which is the SI unit for radiation dose that equals absorbed energy/tissue mass (Baes, n.d.). Besides killing the cells, the radiation can also create mutations that cause the cells to start diving uncontrollably, making them carcinogenic. Iodine is normally absorbed by the thyroid gland to make thyroxine hormone. Because of this, radioactive iodine is likely to accumulate in the thyroid increasing the risk for thyroid cancer (Hasegawa et al., 2015).

        The source of understanding the potential effects of the Fukushima radiation mainly come from epidemiological studies based on the Chernobyl accident in 1986. Due to an extreme power surge, the nuclear reactors in Chernobyl exploded, causing them to burn for 10 days straight and led to more than 115,000 people being evacuated (Chernobyl Accident and Its Consequences, n.d.). Through longitudinal cohort studies of this population, they were able to determine that children affected by the radiation had a higher incidence of thyroid cancer (Cardis et al., 2006). The odds of getting cancer among children who had high radiation exposure (more than 1Gy) was 5 times greater than the odds of getting cancer among children who had low radiation exposure (less than 0.3Gy) (Cardis & Hatch, 2011). Another longitudinal cohort study determined that even after two decades, there was a clear linear dose-response relationship of 1.91 Excess Relative Risk/Gy, demonstrating for every gray of radioactive iodine absorbed, one had 1.91 times higher risk of developing thyroid cancer (Brenner et al., 2011). These sources demonstrate the adverse risk of cancer associated with increased radioactive iodine exposure. I did not find sufficient animal studies to support this data, but believe it is because there is already a vast amount of strong epidemiological data from the Chernobyl accident, as well as from the Nagasaki and Hiroshima bombings to demonstrate the relationship between radioactive iodine and the incidence of thyroid cancer.

        The primary types of studies that were done and are still being done after the Fukushima nuclear plant accident are longitudinal cohort studies similar to those done after the Chernobyl accident with their exposure of interest being radioactive iodine and their outcome of interest being the incidence of thyroid cancer. Their population of interest is the residents that were living in the Fukushima prefecture at the time of the earthquake and nuclear accident. I think that this type of study is appropriate because it is important to note the changes in the radiation levels in their body as time goes on. Furthermore, health effects from the radiation, such as incidence of cancer, cannot be detected right away; it could take years to decades as they saw from the Chernobyl incident. This brings up the downsides to longitudinal cohort studies. Studying a set population for many years is very expensive, especially when ensuring a low dropout rate. Furthermore, it was very difficult to measure the thyroid radiation levels for many people using the thyroid monitor because of the flooding and evacuation (Hasegawa et al., 2015).

As I mentioned above, the populations that were most affected by this nuclear accident were the residents, especially the children, that were near the site of the nuclear plant. TEPCO workers were also affected because they had to go back to the nuclear plants to prevent further radiation damage. Furthermore, firefighters and rescue teams that went into the areas of highest exposure to help residents evacuate may have had an increased amount of radiation exposure.

Initial studies have shown that the exposure doses of radioactive iodine among the Fukushima population has been less than a few mSv, and has certainly been lower than the exposure dose of those affected by the Chernobyl accident (Yamashita, Suzuki, Suzuki, Shimura, & Saenko, 2018). Further longitudinal studies have not seen a detectable increase in the incidence of thyroid cancer among the populations that lived closest to the nuclear plant (Yamashita, Suzuki, Suzuki, Shimura, & Saenko, 2018). However, it is still crucial to continue the studies, especially in children who were exposed because they are the most vulnerable and can still develop late onset thyroid cancer (Harada et al., 2014). Also, it is equally important to think about the mental health effects due to this accident. There is a lot of speculation with the residents that the Japanese government is not telling them the full scope of the effects of the radiation, which creates excess stress on top of many of their houses being destroyed and families being separated by the earthquake and nuclear plant (Akiba, 2012). This accident was definitely unexpected. It was the largest earthquake ever recorded in Japan and the subsequent tsunami caused additional damage. Since it was mostly an unavoidable situation, I believe the best way to carry on is to ensure that the risk for the people who were exposed are minimized. Sometimes iodine tablets are recommended. However, the Japanese have a higher intake of iodine consumption than most populations due to their high intake of seaweed. This should replace the radioactive iodine found in their thyroid (Hasegawa et al., 2015).

To further minimize the spread of the radiation, there was a restriction of food distribution from areas that were affected by the radiation. Throughout the nation, there was a daily radiation check on school lunches to ensure they were not contaminated (Hasegawa et al., 2015). There has been continued radiation monitoring and surveys being done in the affected areas to get a comprehensive understanding of the possible health effects (Yamashita, Suzuki, Suzuki, Shimura, & Saenko, 2018). Even in 2018, there is still a big push to continue donations to help with the rebuilding of communities affected by the earthquake and radiation exposure. The government is also trying to get the public more informed by starting radiation education in Japanese high schools (Tsubokura, Kitamura, & Yoshida, 2018).

Some policies have been revised since this accident, including Japan's Basic Energy Plan. Last updated in 2018, this plan is trying to get Japan to move towards renewable energy sources, hopefully decreasing the number of nuclear plants available so that an accident of this magnitude cannot happen again (Japanese Cabinet approves new basic energy plan - World Nuclear News, 2018). The plan from the Convention of Nuclear Safety was updated in 2014 to include consequences of the Fukushima accident to make sure that other countries can also prevent nuclear accidents in the future (Convention on Nuclear Safety, 2017) . However, nuclear power is still the top energy source in Japan to this day making up 20-22% of the generation of electricity (Japanese Cabinet approves new basic energy plan - World Nuclear News, 2018). This demonstrates that there is still a long way to go to push policy so that nuclear power plants can be replaced with safer energy sources, so an accident like this will not happen again.

        Although the epidemiological studies done in Fukushima so far has not found a direct effect of radioactive iodine exposure to thyroid cancer, I still believe that the continuous check on the citizens on their radiation dose and health effects will be beneficial to have a more thorough understanding of the potential adverse effects of different amounts of radiation dosage (Yamashita, Suzuki, Suzuki, Shimura, & Saenko, 2018). Incidence of thyroid cancer, the main health concern for increased radioactive iodine exposure, is not something that appears the next day. As they saw in Chernobyl, it can take years to decades to see the effects and even still they do not know if the full scope of the consequences has been captured. Food monitoring done in public schools is a great way to mitigate the risks, especially since children are the most vulnerable population. I believe that educating the children about the radiation exposure is also critical as well. Hopefully with a population more educated on the adverse effects of radiation, more policy can be implemented to transition the country away from nuclear power sources. I think there also needs to be a push towards providing the residents with mental health help. From my experience in Japan, I know that mental health is not a very open topic for discussion and I'm sure many people have had trouble reaching out for help. I think that there should definitely be more opportunities within the communities for those seeking mental health advice. I also believe the Japanese government need to be more transparent about the situation with the affected population. The Fukushima residents are the ones that have to live with the repercussions of the accident, so the government should inform them and provide aid in any way possible.

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