S. Gaschak

Estimating the exposure of small mammals at three sites within the Chernobyl exclusion zone - a test application of the ERICA Tool

An essential step in the development of any modelling tool is the validation of its predictions. This paper describes a study conducted within the Chernobyl exclusion zone to acquire data to conduct an independent test of the predictions of the ERICA Tool which is designed for use in assessments of radiological risk to the environment. Small mammals were repeatedly trapped at three woodland sites between early July and mid-August 2005. Thermoluminescent dosimeters mounted on collars were fitted to Apodemus flavicollis, Clethrionomys glareolus and Microtus spp. to provide measurements of external dose rate. A total of 85 TLDs were recovered. All animals from which TLDs were recovered were live-monitored to determine (90)Sr and (137)Cs whole-body activity concentrations. A limited number of animals were also analysed to determine (239,240)Pu activity concentrations. Measurements of whole-body activity concentrations and dose rates recorded by the TLDs were compared to predictions of the ERICA-Tool. The predicted (90)Sr and (137)Cs mean activity concentrations were within an order of magnitude of the observed data means. Whilst there was some variation between sites in the agreement between measurements and predictions this was consistent with what would be expected from the differences in soil types at the sites. Given the uncertainties of conducting a study such as this, the agreement observed between the TLD results and the predicted external dose rates gives confidence to the predictions of the ERICA Tool.

Predicting the radiation exposure of terrestrial wildlife in the Chernobyl exclusion zone: an international comparison of approaches

There is now general acknowledgement that there is a requirement to demonstrate that species other than humans are protected from anthropogenic releases of radioactivity. A number of approaches have been developed for estimating the exposure of wildlife and some of these are being used to conduct regulatory assessments. There is a requirement to compare the outputs of such approaches against available data sets to ensure that they are robust and fit for purpose. In this paper we describe the application of seven approaches for predicting the whole-body ((90)Sr, (137)Cs, (241)Am and Pu isotope) activity concentrations and absorbed dose rates for a range of terrestrial species within the Chernobyl exclusion zone. Predictions are compared against available measurement data, including estimates of external dose rate recorded by thermoluminescent dosimeters attached to rodent species. Potential reasons for differences between predictions between the various approaches and the available data are explored.

New Information for Systematics, Taxonomy, and Phylogeography of the Rodent Genus Apodemus (Sylvaemus) in Ukraine

Abstract In 2004, we collected 211 specimens of European field mice (genus Apodemus; subgenus Sylvaemus) from 16 localities in northern, western, central, and southern Ukraine, including the Crimean Peninsula. We used cytochrome-b mitochondrial DNA sequence data to investigate species diversity, distributional patterns, and taxonomy of Apodemus in Ukraine. Sequence data proved useful for species-level discrimination, because the 11 species examined were defined by low levels of intraspecific variation (mean range, 0.00–3.35%) and by high levels of interspecific variation (mean range, 5.37–18.9%). We identified the 211 specimens to 1 of 4 species: A. flavicollis (n = 121), A. sylvaticus (n = 34), A. uralensis (n = 16), and A. witherbyi (n = 40). Although all 4 species are known from Ukraine, this study provides new information about the ranges and population identity for these species in southeastern Europe. For example, our analyses substantiate the marked genetic structure reported for A. sylvaticus and document the presence of northern and southern continental lineages of this species in Ukraine that are hypothesized to have been isolated from each other in glacial refugia approximately 1.5 million years ago (>5% genetic divergence). Banks of the Dneiper River in northern Ukraine represent an area of secondary contact for the 2 lineages. Additionally, although application of A. witherbyi as a species-level name is debatable, examination of our genetic and morphological data supports its validity and priority over junior synonyms A. hermonensis and A. iconicus.

RADIATION ECOLOGY ISSUES ASSOCIATED WITH MURINE RODENTS AND SHREWS IN THE CHERNOBYL EXCLUSION ZONE

This article describes major studies performed by the Chernobyl Centers International Radioecology Laboratory (Slavutich, Ukraine) on radioecology of murine rodents and shrews inhabiting the Chernobyl Exclusion Zone. The article addresses the long-term (1986–2005) and seasonal dynamics of radioactive contamination of animals and reviews interspecies differences in radionuclide accumulations and factors affecting the radionuclide accumulations. It is shown that bioavailability of radionuclides in the “soil-to-plant” chain and a trophic specialization of animals play key roles in determining their actual contamination levels. The total absorbed dose rates in small mammals significantly reduced during the years following the Chernobyl Nuclear Power Plant accident. In 1986, the absorbed dose rate reached 1.3–6.0 Gy h−1 in the central areas of the Chernobyl Exclusion Zone (the “Red Forest”). In 1988 and 1990, the total absorbed dose rates were 1.3 and 0.42 Gy h−1, respectively. In 1995, 2000, and 2005, according to the present study, the total absorbed dose rates rarely exceeded 0.00023, 0.00018, and 0.00015 Gy h−1, respectively. Contributions of individual radiation sources into the total absorbed dose are described.

Variation in mitochondrial DNA control region haplotypes in populations of the bank vole, Clethrionomys glareolus, living in the Chernobyl environment, Ukraine.

Bank vole, Clethrionomys glareolus, specimens have been annually sampled from the radioactive Chernobyl, Ukraine, environment and nonradioactive reference sites since 1997. Exposed voles continually exhibit increased mitochondrial DNA haplotype (h) and nucleotide diversity (ND), observed in the hypervariable control region (1997-1999). Increased maternal mutation rates, source-sink relationships, or both are proposed as hypotheses for these differences. Samples from additional years (2000 and 2001) have been incorporated into this temporal study. To evaluate the hypothesis that an increased mutation rate is associated with increased h, DNA sequences were examined in a phylogenetic context for novel substitutions not observed in haplotypes from bank voles from outside Ukraine or in other species of Clethrionomys. Such novel substitutions might result from in situ mutation events and, if largely restricted to samples from radioactive environments, support an increased maternal mutation rate in these areas. The only unique substitution meeting this criterion was found in an uncontaminated reference site. All other substitutions are found in other haplotypes of the bank vole or in other species. Increased maternal mutation rates do not appear to explain trends in h and ND observed in northern Ukraine. Studies examining ecological dynamics will clarify the reasons behind, and significance of, increased levels of h in contaminated areas.

Effects of radionuclide contamination on leaf litter decomposition in the Chernobyl exclusion zone.

The effects of radioactive contamination on ecosystem processes such as litter decomposition remain largely unknown. Because radionuclides accumulated in soil and plant biomass can be harmful for organisms, the functioning of ecosystems may be altered by radioactive contamination. Here, we tested the hypothesis that decomposition is impaired by increasing levels of radioactivity in the environment by exposing uncontaminated leaf litter from silver birch and black alder at (i) eleven distant forest sites differing in ambient radiation levels (0.22-15μGyh(-1)) and (ii) along a short distance gradient of radioactive contamination (1.2-29μGyh(-1)) within a single forest in the Chernobyl exclusion zone. In addition to measuring ambient external dose rates, we estimated the average total dose rates (ATDRs) absorbed by decomposers for an accurate estimate of dose-induced ecological consequences of radioactive pollution. Taking into account potential confounding factors (soil pH, moisture, texture, and organic carbon content), the results from the eleven distant forest sites, and from the single forest, showed increased litter mass loss with increasing ATDRs from 0.3 to 150μGyh(-1). This unexpected result may be due to (i) overcompensation of decomposer organisms exposed to radionuclides leading to a higher decomposer abundance (hormetic effect), and/or (ii) from preferred feeding by decomposers on the uncontaminated leaf litter used for our experiment compared to locally produced, contaminated leaf litter. Our data indicate that radio-contamination of forest ecosystems over more than two decades does not necessarily have detrimental effects on organic matter decay. However, further studies are needed to unravel the underlying mechanisms of the results reported here, in order to draw firmer conclusions on how radio-contamination affects decomposition and associated ecosystem processes.

Radioadaptive Response Following In Utero Low-Dose Irradiation

Acute radiation exposure is known to cause biological damage that leads to severe health effects. However, the effects and subsequent health implications of exposure to low doses of ionizing radiation are unclear. The purpose of this study was to investigate the effects of low-dose ionizing radiation exposures in utero. Pregnant laboratory mice (BALB/c) were exposed to low-dose Chernobyl radiation [10–13 mSv per day for 10 days] during organogenesis. The progeny were born and weaned in an uncontaminated laboratory, then were exposed to an acute radiation dose (2.4 Sv). Analysis of our end points (litter dynamics, DNA damage, bone marrow stem cell function, white blood cell counts and gene expression) suggests that a low-dose (100–130 mSv) in utero exposure to ionizing radiation is not deleterious to the offspring. Rather DNA damage, white blood cell levels, and gene expression results suggest a radioadaptive response was elicited for the in utero exposure with respect to the effects of the subsequent acute radiation exposure.

The effects of environmental low‐dose irradiation on tolerance to chemotherapeutic agents

The nuclear disaster at Chernobyl, Ukraine, in April of 1986 continues to impact the environment on many different levels. Studies of epidemiological, environmental, and genetic impacts have been prolific since the accident, revealing interesting results concerning the effects of radiation. The long-tailed field mouse, Apodemus flavicollis, was collected from distinct localities near the Chernobyl site and evaluated based on in vivo responses to the current clinically employed chemotherapeutic agents bleomycin (BLM) and vinblastine (VBL), as well as the immune modulator lipopolysaccharide (LPS). Maximum tolerable doses of three different cancer drugs were administered to the rodents from three different lifestyles: native mice living and reproducing in a radioactive environment, native mice living and reproducing in an uncontaminated region, and laboratory-reared mice (Mus musculus BALB/c) with a known sensitivity to the chemical agents tested. The endpoints employed include micronucleus formation, immune cell induction, differential gene expression, and chemotherapeutic side effects such as lethargy and weight loss. In accordance with the well-studied phenomenon termed radio-adaptation, we observed varied tolerance to chemotherapeutic treatment dependent on history of ionizing radiation exposure. The results of the present study demonstrate a differential response to chemotherapeutic treatment with respect to previous levels of radiation exposure, suggesting a potential benefit associated with low-dose radiation exposure. Data reported herein could have a profound impact on the development of novel cancer treatments involving low-dose ionizing radiation.

ENVIRONMENTAL PROBLEMS ASSOCIATED WITH DECOMMISSIONING THE CHERNOBYL NUCLEAR POWER PLANT COOLING POND

Decommissioning of nuclear power plants and other nuclear fuel cycle facilities associated with residual radioactive contamination of their territories is an imperative issue. Significant problems may result from decommissioning of cooling ponds with residual radioactive contamination. The Chernobyl Nuclear Power Plant (ChNPP) Cooling Pond is one of the largest self-contained water reservoirs in the Chernobyl region and Ukrainian and Belorussian Polesye region. The 1986 ChNPP Reactor Unit Number Four significantly contaminated the ChNPP Cooling Pond. The total radionuclide inventory in the ChNPP Cooling Pond bottom deposits are as follows: 137Cs: 16.28 ± 2.59 TBq; 90Sr: 2.4 ± 0.48 TBq; and 239+240Pu: 0.00518 ± 0.00148 TBq. The ChNPP Cooling Pond is inhabited by over 500 algae species and subspecies, over 200 invertebrate species, and 36 fish species. The total mass of the living organisms in the ChNPP Cooling Pond is estimated to range from about 60,000 to 100,000 tons. The territory adjacent to the ChNPP Cooling Pond attracts many birds and mammals (178 bird species and 47 mammal species were recorded in the Chernobyl Exclusion Zone). This article describes several options for the ChNPP Cooling Pond decommissioning and environmental problems associated with its decommissioning. The article also provides assessments of the existing and potential exposure doses for the shoreline biota. For the 2008 conditions, the estimated total dose rate values were 11.4 40 &mgr;Gy h−1 for amphibians, 6.3 &mgr;Gy h−1 for birds, 15.1 &mgr;Gy h−1 for mammals, and 10.3 &mgr;Gy h−1 for reptiles, with the recommended maximum dose rate being equal to 40 &mgr;Gy h−1. However, drying the ChNPP Cooling Pond may increase the exposure doses to 94.5 &mgr;Gy h−1 for amphibians, 95.2 &mgr;Gy h−1 for birds, 284.0 &mgr;Gy h−1 for mammals, and 847.0 &mgr;Gy h−1 for reptiles. All of these anticipated dose rates exceed the recommended values.

OVERVIEW OF THE COOPERATION BETWEEN THE CHERNOBYL CENTERʼS INTERNATIONAL RADIOECOLOGY LABORATORY IN SLAVUTYCH, UKRAINE, AND U.S. RESEARCH CENTERS BETWEEN 2000 AND 2010

The International Radioecology Laboratory (IRL) located in Slavutych, Ukraine, was created in 1999 under the initiative of the United States Government and the Government of Ukraine in the framework of international cooperation on evaluation and minimization of consequences of the Chernobyl nuclear power plant (ChNPP) accident. Since the time the IRL was founded, it has participated in a large number of projects, including the following: 1) study of radionuclide accumulation, distribution, and migration in components of various ecological systems of the Chernobyl Exclusion Zone (ChEZ); 2) radiation dose assessments; 3) study of the effects of radiation influence on biological systems; 4) expert analysis of isotopic and quantitative composition of radioactive contaminants; 5) development of new methods and technologies intended for radioecological research; 6) evaluation of future developments and pathways for potential remediation of the ChEZ areas; 7) assistance in provision of physical protection systems for ionizing irradiation sources at Ukrainian enterprises; 8) reviews of open Russian language publications on issues associated with consequences of the ChNPP accident, radioactive waste management, radioecological monitoring, and ChNPP decommissioning; 9) conduct of training courses on problems of radioecology, radiation safety, radioecological characterization of test sites and environmental media, and research methods; 10) conduct of on-site scientific conferences and workshops on the ChEZ and radioecology problems; participation in off-site scientific conferences and meetings; and 11) preparation of scientific and popular science publications and interactions with mass media representatives. This article provides a brief overview of the major achievements resulting from this cooperation between the IRL and U.S. research centers.