04/14/2011 - 07:15

Wildlife and Chernobyl: The scientific evidence for minimal impacts

Robert J. BakerJeffrey K. Wickliffe

Robert J. Baker

Baker is Horn Professor of Biology at Texas Tech University in Lubbock, TX. He has worked on the...

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Jeffrey K. Wickliffe

Wickliffe is an assistant professor of environmental health sciences at the Tulane University School of...

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The ongoing Fukushima disaster will inevitably provoke a new examination of the biological effects of radiation from nuclear accidents, and it has already had a major influence on nuclear power initiatives worldwide. At present, the extent and levels of radioactive contamination around the reactor and in the affected Japanese prefectures is unknown, so any predictions of the effects on human and ecological populations would rely on mere speculation. However, our experience with the native fauna exposed to the Chernobyl environment may provide some insights.

The Chernobyl meltdown 25 years ago created a unique biological laboratory in which a broad array of living organisms in a few areas received extremely high, acute radiation doses over the first few months followed by a chronic, continuing exposure to decreasing levels of radiation. In these few areas, individuals of some of the species of fauna and flora receiving the highest acute doses did not survive. After the doses decayed to a point of sub-lethal exposure, the remaining fauna as well as the returning fauna experienced multigenerational exposure during all stages of their life cycles. This provided a unique opportunity to study the biological consequences resulting from chronic exposure to radiation in the environment.

Over the last 25 years, there have been hundreds of papers published on the environmental and biological impacts of the Chernobyl accident. A review of this literature presents a confounding complexity of opinions and conclusions about the significance of the Chernobyl meltdown to life. While some research concludes that chronic exposure to Chernobyl radiation is having a devastating effect on a broad array of organisms in and near the restricted areas around the failed reactor complex, other research -- some of it conducted by us and our colleagues -- does not document such negative biological effects, even among fauna that experienced chronic exposure to the highest levels of Chernobyl radiation throughout all of their life cycles.

Our first papers, in 1996, indicated that the abundance of individuals and biodiversity was as high or higher in the most radioactive regions when compared to the areas with little or no radiation. Our publications included many different types of data and included the use of transgenic mice -- ones engineered to study mutation rates -- that were exposed in the most radioactive regions in the highly contaminated zone known as the Red Forest, as well as chromosomal breakage and mutation studies in native mice. Our work also included studies documenting survival and reproduction of female bank voles over two years.

These studies documented essentially no statistically supported negative effect on bank voles living in the Chernobyl environment. We note that these results are compatible with those of independent experimental field studies on very similar species. Among these studies are ones from independent groups and individuals such as Ron Chesser's team at Texas Tech; J.T. Smith's program at the Centre for Ecology and Hydrology in Dorchester, UK; and Steve Mihok of the Canadian Nuclear Safety Commission.

Our group also published a paper in 1996 in Nature that reported an elevated mutational rate in two species of voles living in the Red Forest. Because we had archived the clones that were sequenced from the gene used in those studies, we were able to exactly replicate our initial studies using automated DNA sequencers that became available to us immediately after the Nature paper was published. When this more accurate sequencing was completed, the data were no longer significant when comparing highly exposed and unexposed samples. After sequencing all of the clones multiple times and repeatedly finding no statistically significant differences, we retracted our Nature paper.

A December 2010 New Yorker article concerning the nature of the scientific process generally indicates that conflict in interpretation of results and their significance to society is common in science. The article concludes that, in many cases, published extraordinary scientific data prove to be unsupported by further scientific studies, but the implications of the original data continue to be accepted by society because "they make sense." We experienced this first-hand. Extensive television and major newspaper coverage attended our 1996 paper that showed a deleterious effect of radiation exposure, but scant attention was paid to our 1997 retraction.

What we know from Chernobyl. What do we know about the environmental effects of Chernobyl, the world's worst nuclear power plant disaster? Some salient points follow.

  1. There is a great difference in the ability of trees to respond to huge doses of radiation. Scotch pines are highly sensitive; the Red Forest gets its name from the red-brown color of the dead Scotch pine trees, killed by radiation exposure in 1986. Today, even though the amount of radiation has been greatly reduced by decay, Scotch pines are only now beginning to grow in the unremediated Red Forest region. On the other hand, birch trees survived the radiation; these trees continue to grow, are beautiful, and appear healthy.  But the response of the Scotch pines is an obvious example of the negative effects of exposure to radiation.
  2. Within 10 years after the accident, all of the native species of small mammals that would be expected to be present in the Red Forest were collected there. As the trees and other flora in the Red Forest experienced ecological succession, the mammalian fauna changed. For example, when we first visited the Red Forest region in 1994, grassland was dominant. Voles and field mice -- expected in a grassy environment -- were commonly found. As forest replaced grasslands, bank voles and species of wood mice associated with forests became common and dominant. The significance of this is that population dynamics and species distribution were as expected based on local ecology and not on the presence, or absence, of radiation.
  3. The work of Chesser's team shows that the radionuclides present in individual animals varied substantially even in different species living in the same location. Bank voles were the most radioactive; the common wood mouse and shrews were the least radioactive. Even though bank voles had the highest radioactive body burden, they were the most common small mammal in the most radioactive regions.
  4. In the unremediated Red Forest (400 hectares, west of the destroyed reactor) and the area of the northern plume extending less than 12 kilometers from the reactor, large mammals such as Russian wild boar, wolves, moose, and roe deer, as well as fish hawks (ospreys), were more common than in clean areas outside the restricted zones. The northern plume area near Glyboke Lake was always a joy to visit because of the abundance of large animals. Glyboke Lake now appears analogous to a protected national park, such as Yellowstone.
  5. Although some mammalian species such as wolves, raccoon dogs, European badgers, and red deer were not observed by normal research activities in the Red Forest and Glyboke Lake regions, they were commonly photographed by automatic trail cameras.
  6. We know that normal farming and ranching in the areas adjacent to the restricted zone around Chernobyl resulted in a lower population density of most mammalian species when compared to their abundance in the most radioactive regions of the Red Forest. The exception was symbiotic house mice, which were not present in the towns and houses abandoned by humans in the contaminated Chernobyl zone, but were common near homes inhabited by humans outside of the zone. Importantly, house mice weren't only absent in the radioactive abandoned towns; they were also absent from abandoned towns in the zone where little or no radiation was present. We conclude that it was the presence or absence of humans -- -not radiation -- -that influenced the abundance of house mice.
  7. We know that there has been continuous, varying, multigenerational exposure of native vertebrates, including small mammals (bank voles, mice, shrews, and moles) and lower vertebrates (snakes, frogs, salamanders, and fish). Results from our research on bank voles did not find any tumors in a single individual of more than 400 necropsied bank voles. The population densities and health of the individuals of the bank voles are indistinguishable from populations present in clean areas.

The need for additional research. After the first post-Chernobyl decade, there was minimal sustained funding of research programs to document the biological effects of chronic exposure to radioactive contamination in the region's ecosystem. Most of the experimental results from the Chernobyl ecosystem are anecdotal in comparison with the science produced on the survivors of the 1945 Hiroshima and Nagasaki atomic bombings. More and better research is needed.

What researchers have not studied is whether or not multigenerational exposure to the radioactive environment created by the meltdown at Chernobyl resulted in an increase in genetic mutations that could produce birth defects and reduced survival fitness. The health of these populations in the most radioactive regions suggests no major impacts on fitness are likely. However, this question can be answered with an experimental design. The cost of the necessary laboratory breeding needed to perform such a study would be less than $1.5 million. This is an important question to answer in terms of assessing future radiation releases, but it's important for other reasons, too. If chronic mutigenerational exposure at the high radiation levels in the Red Forest bank voles does not increase mutational load, then, for example, human space travel to Mars -- which will result in high chronic radiation doses to the astronauts -- may not be as dangerous to the astronauts' health as some models predict.

How can society make sense of conflicting studies, and how can society logically understand the published data on Chernobyl pollution? Our team has struggled with this question and has questioned our ability, as well as that of others, to design scientific experiments that best describe risks and consequences of the Chernobyl accident. Our approach has been to study the level of radioactive contamination in the exclusion zone and design experiments to study species from the most radioactive environments. In addition, all of our team's studies have been conducted double-blind, and all biological samples have been frozen or alternatively preserved to be archived with exact location data and the date and origin of the samples so that future studies can be conducted by us and others.

There are enough papers published documenting the negative effects of Chernobyl radiation that certain patterns can be seen. One example involves barn swallows. A 2001 paper described the negative effects that closure of dairy farming had on local abundance, distribution, and reproduction of barn swallows in Europe, concluding that the abundance of barn swallows decreased at a specific locality significantly when a dairy farm closed, with an average reduction of 48 percent. After the Chernobyl meltdown, all farming activities and human inhabitants were removed from the contaminated zone, an action that would be expected to substantially reduce the barn swallow population. Yet the 2001 paper is never cited in the numerous papers written on the effects of radiation on barn swallows in the Chernobyl area. Rather, all of the reductions in barn swallow populations accounted for in these papers are proposed to be from negative effects of Chernobyl radiation, not from the subsequent evacuation of farming activities.

We emphasize that our research has focused on examining the genetic effects in small, resident mammals living in the major plumes created by the release; these sites are some of the most radioactive areas created by the meltdown. Bank voles, as well as other rodent species we have studied, experience doses several orders of magnitude greater than anything recorded for virtually all other vertebrates studied. Yet some other studies assert detrimental effects from radiation in areas with reported levels of radiation that were comparable to background levels. Furthermore, some of these surveys conclude that the magnitude of the effects depend on differences in dose that are so small that they are comparable to the differences in natural radiation doses received by organisms living along the US Gulf Coast compared with those living on the Colorado Plateau.

The extent to which the Chernobyl environment has negative effects on life has implications for space travel, future nuclear accidents, dirty bombs, workers in a variety of mines, and even airline travel. The data from the natural laboratory created by the Chernobyl disaster is valuable to society -- and to predicting future effects from Fukushima -- only if it is produced from properly designed experiments and unbiased experimenters and meets the scientific requirement of being statistically significant. We retracted our Nature article not because it pleased us, but because it was how science should be conducted if it is to be of value to society. If there is a conflict or inconsistency between studies of the same contaminants, it is also appropriate to carefully examine the nature of the science that produced different results. It is important to society to understand which result most accurately describes risk and biological consequences to exposure.

For scientists to do the best possible job assessing the effects of environmental radiation, archives of all clones, tissues, microscope slides, specimens, or any other biological or genetic material used in such studies should be established and made available for other scientists for future study. It is not unreasonable that every paper that presents a position on the biological consequences of chronic exposure to radiation at Chernobyl be designed to facilitate replication of the experiments.

The ultimate effects that the Fukushima accident has on the environment are impossible to predict at this time because of the evolving and fluid nature of the situation. Based on the current lack of consensus regarding the effects of environmentally released radiation, post-Fukushima predictions may well be fraught with considerable uncertainty. Twenty-five years after the Chernobyl meltdown, the scientific community has not yet been able to provide a clear understanding of the spectrum of ecological effects created by that radiological disaster. Perhaps the accident in Japan will serve to highlight again the undeniable fact that our scientific grasp of radiation risk to the environment is surprisingly limited.

Acknowledgments. We thank Ron Chesser and Heather Meeks for verification of our observations and for valuable discussions.

Editor's note: The current issue of the Bulletin's digital journal titled "Chernobyl: Looking back, moving forward" reflects on the 25-year anniversary of the Chernobyl tragedy.