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| Fig. 1:Radiation warning sign in the countryside inside the exclusion zone. (Source: Wikimedia Commons) |
Following the Chernobyl Nuclear Power Plant Accident of 1986, a number of studies were conducted to assess the health consequences of the accident. The accident released radiogenic compounds that contaminated substantial areas, particularly in Belarus and the western areas of Russia and Ukraine (then part of the USSR), as all as other countries in Western Europe to a lesser degree. [1] Some areas immediately surrounding Chernobyl belong, to this day, to an exclusion zone, where public access and settlement are not allowed due to the radiation levels. Fig. 1 shows a radiation warning sign marking an area in the exclusion zone as dangerous. The Chernobyl accident resulted in the release into the atmosphere of radionuclides of about 8 exabecquerel (8 × 1018 Bq). A sharp increase in cases of pediatric thyroid cancer in children born within a 150 km radius from the Chernobyl power plant has led researchers to believe that short-lived radioactive fallout following the accident is responsible for this sudden spike. [2]
Thyroid cancer is one of many radiogenic diseases. Other such diseases include leukemia, breast cancer, autoimmune thyroiditis, cardiovascular disease, and cataracts. During the initial period after the accident the most biologically significant isotopes released in the fallout were radioiodines, primarily I-131 and the shorter-lived isotopes I-132 and I-133. Absorption of radioiodines can occur from ingestion of contaminated food and water as well as through inhalation. Absorption can lead to serious internal exposure of the radioiodines to the thyroid gland. Radioiodine absorption, however, is not the only way the thyroid glands can get exposed to radiation. Additional sources of radiation to the thyroid can come from protracted gamma radiation from external sources and internal exposure caused by longer-lived isotopes, such as cesium, strontium, and plutonium. [3] The thyroid gland is active and has bigger relative size during childhood and adolescence, which is why the effect of ingesting or inhaling radioactive I-131 is more pronounced in young people than in adults. [4] In 2012, a Conference on Radiation and Health took place in Kennelbunkport, Maine, where many scholars discussed new data surrounding the relationship between the Chernobyl accident and pediatric thyroid cancer incidence. Dr. Michael Abend from the Bundeswehr Institute of Radiobiology in Germany identified several specific gene candidates that can result in thyroid cancer after exposure to I-131 radiation released after the Chernobyl accident. [5]
In 1998-2000, the Belarus Health Ministry in collaboration with the Gomel Regional Health Department conducted a study on children born from Jan 1, 1983, to Dec 31, 1989, and who were living in the districts of Rechitskii, Loevskii, Gomelskii, and Hoynikskii, and Gomel City, in the Gomel region of Belarus. All of these areas are located within a 150 km radius from the accident site. The study examined thyroid glands by ultrasound, and measured concentrations of free thyroxine, a thyroid-stimulating hormone. The study split the 21601 children it examined in three groups: Group 1 was comprised of children born between Jan 1, 1983 and April 26, 1986, (i.e. children who were infants or toddlers at the time of the accident). Group 2 was comprised of children born between April 27 and December 31, 1986 (i.e.ie in the eight months immediately succeeding the accident). Finally children born between Jan 1, 1987 and Dec. 31, 1989 belonged to Group 3. While there were no instances of thyroid cancer in the Group 3 children and only one case in the Group 2 children, born in 1986 after the Chernobyl accident, there were 31 cases (or 0.32%) of thyroid cancer in the Group 1 children. When adjusted for sex and age, these results show a statistically significant (p=0.006) effect of exposure to fallout after Chernobyl in the frequency of thyroid cancer in the three groups. The conclusion of the study was that thyroid cancers detected in children after the Chernobyl accident were likely to have been caused by direct external or internal exposure to short-lived components of radioactive fallout, such as I-131 (whose half-life is half-life 8.04 days) and I-133 (whose half-life is 20.8 hours). [2]
In conclusion, there is evidence to support a correlation between exposure to radioactivity and thyroid cancer, particularly for children. A number of studies have been conducted on children exposed to radioactivity due to the Chernobyl accident, primarily in Belarus, a country whose southern region was one of the most contaminated areas after the accident. Most of the iodine isotopes suspected of causing thyroid cancer are relatively short-lived. This accounts for why children born in the years after the accident were less at risk.
© Nefeli Ioannou. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] G. R. Howe, "Leukemia Following The Chernobyl Accident," Health Phys. 93, 512 (2007).
[2] Y. Shibata et al., "15 Years After Chernobyl: New Evidence of Thyroid Cancer," Lancet 358, 1965 (2001).
[3] Y. Nikiforov and D. R. Gnepp, "Pediatric Thyroid Cancer After The Chernobyl Disaster. Pathomorphologic Study of 84 Cases (19911992) From the Republic of Belarus," Cancer 74, 748 (1994).
[4] O. Urban, "Health Consequences of the Chernobyl Accident," Physics 241, Stanford University, Winter 2016.
[5] N. Barnett, "Chernobyl's Effect on Cancer Levels in Eurasia ," Physics 241, Stanford University, Winter 2014.
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