Brenda E. Rodgers

Consequences of Polluted Environments on Population Structure: The Bank Vole (Clethrionomys glareolus) at Chornobyl

The accident at the Chornobyl Nuclear Power Plant in April 1986, released 100–200 million Curies of radioactive material into the surrounding environment. To investigate the possible genetic and population effects resulting from chronic exposure to this environmental radiation, we have examined mitochondrial DNA (control region) sequences from bank voles, Clethrionomys glareolus, inhabiting contaminated sites. Our analysis indicates genetic diversity is elevated in the contaminated sites when compared to relatively uncontaminated reference sites. This may be attributed to either an increased mutation rate in the mtDNA control region or immigration of individuals from surrounding areas into the contaminated environment. Although our observations do indicate that the contaminated areas represent sink populations, we cannot statistically discriminate between these two alternatives at this time. In addition, we have been unable to attribute any significant detrimental effects to bank vole populations inhabiting the contaminated Chornobyl environment based on these data. This is particularly paradoxical considering bank voles in the contaminated areas harbor the highest radiocesium (137Cs) body burdens and external dose rates of any mammal ever measured. Our long-term research on the bank vole indicates that several factors, including contaminants, may affect haplotype dynamics both spatially and temporally. These multifarious influences subsequently affect population genetic estimates typically used to address the effects of environmental pollution on animal populations. Finally, we provide a general framework for designing experiments investigating the role contaminants play in altering the genetic characteristics of exposed populations.

Reconstruction of radioactive plume characteristics along Chernobyl’s Western Trace

Using data obtained from 435 radiation sampling stations in the Red Forest, 1.5 km W if the Chernobyl Nuclear Complex, we reconstructed the deposition pathway of the first plume released by the accident, Chernobyls Western Trace. The dimensions and deposition rates of the plume remain sharply defined 15 years after the accident. Assuming a uniform particle distribution within the original cloud, we derived estimates of plume dimensions by applying geometric transformations to the coordinates at each sample point. Our derived estimates for the radioactive cloud accounted for 87% of the variation of radioactivity in this region. Results show a highly integrated bell-shaped cross-section of the cloud of radiation, approximately 660 m wide and 290 m high, traveling at a bearing of 264 degrees from reactor IV. Particle sizes within Chernobyls Western Trace were within the most dangerous range for inhaled aerosols (2-5 microm). Therefore, reconstruction of the dispersion of such particles is critical for understanding the aftermath of nuclear and biological aerosol releases.

Mitochondrial DNA Heteroplasmy in Laboratory Mice Experimentally Enclosed in the Radioactive Chernobyl Environment

Abstract Wickliffe, J. K., Rodgers, B. E., Chesser, R. K., Phillips, C. J., Gaschak, S. P. and Baker, R. J. Mitochondrial DNA Heteroplasmy in Laboratory Mice Experimentally Enclosed in the Radioactive Chernobyl Environment. Radiat. Res. 159, 458–464 (2003). Mitochondrial DNA heteroplasmy using the protein-coding cytochrome b (Mtcyb) gene was assessed in laboratory mice (C57BL/6 and BALB/c) exposed to the Chernobyl environment. Subacute to subchronic (30–40 days) exposure resulted in a cumulative radiation dose of 1.2–1.6 Gy (∼0.04 Gy/day). Mice were sampled prior to introduction into the enclosures and again after removal from the enclosures. Nucleotide variation (site heteroplasmy) in 306 pre-exposure Mtcyb gene copies (122,400 base pairs) was compared to variation in 354 postexposure gene copies (141,600 base pairs). Five mutant copies, each characterized by a single nucleotide substitution, were observed (four in the pre-exposure samples, one in a postexposure sample). The frequencies of mutant gene copies and nucleotide substitutions in pre-exposure and postexposure samples were not significantly different. This suggests that this type of exposure (i.e. low dose rate) does not pose a significant mutation risk to the Mtcyb gene in digit tissue. Furthermore, no significant radiation risk to analogous human tissues may exist when occupational exposures involve low dose rates such as these. Finally, linear, cumulative models of genetic risk currently used to estimate radiation-induced effects are likely to be inappropriate for low-dose-rate exposures and need to be re-evaluated critically.

RADIO-ADAPTIVE RESPONSE TO ENVIRONMENTAL EXPOSURES AT CHERNOBYL

The genetic consequences resulting from environmental exposure to ionizing radiation have a significant impact on both radiation regulatory policies and the comprehension of the human health risks associated with radiation exposure. The primary objectives of the study were to assess 1) genotoxicity of exposure to radiation as a function of absorbed dose and dose rate, and 2) induction of a radio-adaptive response following a priming dose at varying dose rates. Results demonstrated that sub-acute environmental exposures of 10cGy gamma radiation resulted in indistinguishable levels of chromosomal damage as compared to controls. A radio-adaptive response was observed in all experimental groups, exposed to a subsequent acute challenge dose of 1.5 Gy, demonstrating that low dose rates of low energy transfer (LET) radiation are effective in reducing genetic damage from a subsequent acute low-LET radiation exposure. Furthermore, the data presented herein demonstrate a potential beneficial effect of sub-chronic exposure to low levels of low-LET radiation in an environmental setting and do not support the Linear No Threshold (LNT) hypothesis.

UNDERSTANDING THE GENETIC CONSEQUENCES OF ENVIRONMENTAL TOXICANT EXPOSURE: CHERNOBYL AS A MODEL SYSTEM

We sampled vole populations in Ukraine with the dual goal of characterizing population diversity and of providing a biogeographic perspective to evaluate experimental designs used for previous studies. Our data indicate that genetic diversity in bank vole populations is widely variable across regions and that diversity estimates in contaminated sites are unremarkable compared to those in uncontaminated areas. Furthermore, the relative frequencies of haplotypes have remained statistically identical throughout multiple sampling periods. Thus, the genetic data from bank vole populations in Ukraine fail to support the hypothesis that mutational changes in contaminated regions are the product of exposure to Chernobyl radiation. Our results suggest that genetic diversity in radioactive regions of Ukraine is probably a function of natural geographic variation rather than increased mutational pressure from radiation exposure and underscore the importance of adequate geographic sampling in studies designed to elucidate the effects of toxicant exposure.

Mitochondrial control region variation in bank voles (Clethrionomys glareolus) is not related to Chernobyl radiation exposure.

Three previous studies at Chernobyl, Ukraine, documented elevated mitochondrial DNA diversity in bank voles (Clethrionomys glareolus) from radioactively contaminated sites. Little evidence was found to link patterns of diversity in contaminated areas to radiation exposure, but the experimental design precluded discriminating among alternative explanations for elevated diversity in exposed groups. Reference sites selected for the studies were relatively distant from contaminated sites and, additionally, were separated from contaminated sites by large river systems; thus, we hypothesized that differences among sites were correlated with geographic isolation rather than with radiation exposure. For the present study, we added three reference sites, which were selected based on minimal radioactive contamination, proximity to contaminated sites, and absence of obvious barriers to dispersal. We hypothesized that neighboring reference sites should exhibit levels and patterns of diversity similar to those of contaminated sites if the previously detected differences were, in fact, caused by geographic isolation. Indeed, levels of diversity in nearby reference sites are comparable to levels in contaminated sites. Additionally, nearby reference sites contain several haplotypes not observed at other study sites. Our results suggest that levels of diversity in contaminated regions are more plausibly explained by ecological and historical factors than by increased mutational pressure resulting from exposure to Chernobyl radiation.

Piecing Together Iraq’s Nuclear Legacy

A forensic investigation of radioactive contamination at Iraq’s central nuclear research center confirms Saddam’s nuclear program never made it off the ground, but it did endanger Iraqis.

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.

IDENTIFYING VOUCHER SPECIMENS INVOLVING RISK: SHREWS FROM CHORNOBYL, UKRAINE

Abstract Specimens may pose a risk to personnel handling them such as the radioactive fauna collected from contaminated areas in Chornobyl. To minimize radiation exposure and to evaluate an inexpensive molecular tool in identifying species of shrew, we analyzed DNA sequences from the cytochrome-b gene. Specimens were visually identified as Sorex araneus, S. minutus, and Neomys fodiens, and morphological variants were noted that could represent additional species. Cytochrome-b sequences indicated the apparent variants represented intraspecific polymorphisms. This approach substantially reduced exposure to radioactivity present in the archived material. Excluding salaries and cost of equipment, the analytical cost per specimen was US