Published: July 11, 2011
Oddly enough, the 25th anniversary of the worst nuclear accident in history has been marked by journalism about animals. Two magazines, Wired and Harper’s, have published lengthy articles about the rebirth of animal life in the so-called exclusion zone around the Chernobyl nuclear plant in Ukraine.
All well and good, but given the recent Japanese
nuclear accident, wouldn’t you rather know what has happened to the,
er, people who were affected by Chernobyl?
Is Chernobyl a Wild Kingdom or a Radioactive Den of Decay?
April 14, 2011
Wired May 2011
Life in the zone:
BOOSTER SHOTS: Oddities, musings and news from the health world
April 26, 2011 |By Eryn Brown, Los Angeles Times
The Lancet Oncology, Volume 12, Issue 5, Pages 416 - 418, May 2011
doi:10.1016/S1470-2045(11)70095-XCite or Link Using DOI
Published Online: 26 April 2011
25 years after Chernobyl: lessons for Japan?
On April 25, 1986, operators shut down unit 4 of the power plant at Chernobyl, in the former Soviet Union, to test the emergency power system in the event of power loss. The nuclear reactor—a different type than those damaged in the recent tsunami in Japan—was a graphite-moderated light water reactor that is now considered obsolete for use, although it still remains in use in some parts of the former Soviet Union. As with most nuclear power plants, uranium fission led to thermal generation, heating water to provide steam for electricity generation. However, because of the test of the backup system, the water that was used to cool the reactor was lost, resulting in overheating, a power surge and steam explosion, and destruction of the reactor core at 0123 h on April 26, 1986.
Unlike the reactors in Japan, the Chernobyl reactor was not in a reinforced shell, and the roof of the power plant essentially blew up. This explosion released tonnes of nuclear fuel (about 8—180 metric tonnes) and fission products (3—9 billion Ci) into the air, which were then blown northwest by the winds. The exact quantities of released products might never be known because of insufficient dosimetry calculations within the first several days after the accident. Several workers were immediately killed in the explosion, and 100 firefighters received extensive radiation exposure when putting out the fire. The graphite in the reactor burned for 10 days and substantial radiation was released for about 20 days. 100—200 workers were diagnosed with acute radiation syndrome with about 30 dying early and another 14 dying over the next 10 years.
The major radionuclides released during the accident were radioactive iodine (131I) and caesium (134Cs and 137Cs), and, to a lesser extent, radioactive strontium (89Sr and 90Sr) and plutonium (234Pu). The half-life of 131I is 8 days, therefore, after contaminating the food chain, dissipated fairly soon. However, radioactive caesium products have half-lives between 2 years and 30 years and continue to contaminate large areas around Chernobyl. Strontium has a half-life ranging between 52 days and 28 years, with the same issues of prolonged contamination as caesium. Plutonium has a half-life of 24 400 years. 400 times more radioactivity was released from the Chernobyl power plant than from the Hiroshima atomic bomb; by contrast, the atomic weapons testing of the 1950s and 1960s released about 100—1000 times more than the Chernobyl accident. The areas most affected by the Chernobyl release were Russia, Ukraine, and Belarus; however, other European countries and the rest of the world received some exposure, albeit at lower levels than the regions surrounding Chernobyl.
More than 800.000 personnel were involved in the clean up, and more than 200.000 workers received varying degrees of exposure, as did about 100.000 evacuees. 270.000 people in the most contaminated areas received small to moderate doses of radiation (about 5—500 mSv). In comparison, a chest radiograph exposes a person to 0,1 mSv, whereas a CT scan of the chest results in exposure to 6—18 mSv. Direct comparisons of the doses are difficult because the harmful effects from ingested radionuclides that expose a person for several days are different to exposure from split-second external gamma beams.
After the Chernobyl accident, many scientific papers reported the cancer consequences of the event. We participated in writing the first major UN report about the effects of the accident and, in 2002, summarised the existing published work. We concluded that, with the exception of thyroid cancer in young people, there was no strong evidence to suggest that excess cancer incidence was substantial in the aftermath of the accident. Several investigators have shared this conclusion. In this Comment, we aim to emphasise several studies that show the complexities faced when the health consequences of the Chernobyl accident are studied. Two subsequent studies[4, 5]—which provided evidence associating Chernobyl-related radiation and thyroid cancer in children—used population-based, case—control study designs, collated detailed information for individual dosimetry, and used thoughtful and sophisticated statistical approaches. Combined with past evidence, results from these studies leave little doubt that excess childhood thyroid cancer is a result of the accident. These findings should influence the decision to implement potassium iodine supplementation if similar scenarios should occur in the future.
Although we published work in 2005 that reported a possible increase in childhood leukaemia in Belarus, Ukraine, and Russia, we acknowledged that most of the controls were selected from regions that were largely unaffected by the accident, which led to significant associations that were not biologically plausible. This scenario shows the considerable logistical challenges in doing epidemiological research in countries of the former Soviet Union. Little expertise in chronic epidemiology at the time, language barriers, cultural differences, and the daily challenges in covering a very large study area were probable contributors to the flawed study design. Furthermore, an increase in rates of breast cancer was reported in Belarus and Ukraine. Although this study used a descriptive design, dose estimates were calculated on the basis of local contamination data. Ideally, this study should be followed up with an analytical epidemiological study focusing on women who were in puberty at the time of the accident.
Data from the Japanese Life Span Study suggested that the highest excess risk was for women who were in puberty at the time of the atomic bombing. Another sensitive time-point is lactation at the time of the accident, when the likelihood of radionuclide absorption to the mammary tissue is high. Despite the scientific interest and biological plausibility, there are several serious threats to the feasibility of such an investigation in the most affected regions. Unless government sponsored, to secure funding for a project of this scope will be a great challenge. Another issue is the collection of valid dosimetry data for dose reconstruction 25 years after the accident—eg, women might be unable to recall personal behaviour and food consumption during the crucial window of time. Another area of investigation would be risk of lung cancer. However, as for a study of breast cancer, substantial logistical challenges threaten the feasibility and validity of such investigations. Additionally, the separation of any radiation effects from the overwhelming influence of tobacco exposure in the development of lung cancer might not be possible.
Much is still unknown about the extent to which human error was involved into the recent accident at the Fukushima nuclear power plant in Japan. The inability to anticipate and react to the loss of power to cooling systems seems to have resulted in severe damage to the nuclear core, with release of radionuclides as seen in the Chernobyl accident. Aggressive efforts will be needed to limit exposure to radioactive iodine and caesium, and to isolate contaminated areas. In particular, children and young adults are at highest risk because of past data showing that exposure at young ages increases the risk of adverse health effects such as thyroid cancer.
Sadly, the ongoing events in Japan might offer another opportunity to study the cancer consequences of accidents at nuclear power plants. Although Japan is facing many challenges in the aftermath of three simultaneously occurring disasters, the country's long history in epidemiological research of radiation might place it in a better position to study the consequences of the nuclear power plant accident and to implement research investigations in a shorter timeframe than can other countries with less experience. Unlike the former Soviet Union, Japan is a more open society and did not attempt to hide the radiation release from its citizens. Japan is also a politically and economically stable society. Major challenges in doing valid research after the Chernobyl accident were associated with the political instability after the collapse of the former Soviet Union in 1991 and with the scarcity of funding from the new independent countries that were most affected by the accident.
However, in Japan, the political, economical, and scientific environment should allow for comprehensive investigations of the health consequences of a major accident at a nuclear power plant. Findings from such studies should be useful in informing the public about expectations of these health effects, and should guide public health officials in implementing an effective medical response.
The authors declared no conflicts of interest.