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Currently, the effects of chronic, continuous low dose environmental irradiation on the mitochondrial genome of resident small mammals are unknown. Using the bank vole (Myodes glareolus) as a model system, we tested the hypothesis that approximately 50 generations of exposure to the Chernobyl environment has significantly altered genetic diversity of the mitochondrial genome. Using deep sequencing, we compared mitochondrial genomes from 131 individuals from reference sites with radioactive contamination comparable to that present in northern Ukraine before the 26 April 1986 meltdown, to populations where substantial fallout was deposited following the nuclear accident. Population genetic variables revealed significant differences among populations from contaminated and uncontaminated localities. Therefore, we rejected the null hypothesis of no significant genetic effect from 50 generations of exposure to the environment created by the Chernobyl meltdown. Samples from contaminated localities exhibited significantly higher numbers of haplotypes and polymorphic loci, elevated genetic diversity, and a significantly higher average number of substitutions per site across mitochondrial gene regions. Observed genetic variation was dominated by synonymous mutations, which may indicate a history of purify selection against nonsynonymous or insertion/deletion mutations. These significant differences were not attributable to sample size artifacts. The observed increase in mitochondrial genomic diversity in voles from radioactive sites is consistent with the possibility that chronic, continuous irradiation resulting from the Chernobyl disaster has produced an accelerated mutation rate in this species over the last 25 years. Our results, being the first to demonstrate this phenomenon in a wild mammalian species, are important for understanding genetic consequences of exposure to low‐dose radiation sources.

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Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trade marks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. AbstractAn 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 ERICATool 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.

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.

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.

23Environmental impacts of the 1986 Chernobyl Nuclear Power Plant accident are much 24 debated, but the effects of radiation on host microbiomes has received little attention to date. 25We present the first analysis of small mammal gut microbiome from the Chernobyl Exclusion 26Zone in relation to total absorbed dose rate and including caecum as well as faeces sample. 27The associations between microbiome communities and radiation exposure varied between 28 host species. Associations between microbiome and radiation was different for analyses 29 based on ambient versus total weighted absorbed dose rates. We found considerable 30 variation between patterns for faecal and gut samples of bank voles, suggesting faecal 31 samples are not an accurate indicator of gut composition. For bank vole guts, associations 32 between radiation and bacterial community composition were robust against geographical 33 and habitat variation. We found limited associations between radiation and fungal 34 communities. Host physiological mechanisms or environmental factors may be driving these 35 patterns. 100Chornobyl Center's main laboratory (R 2 = 0.98). The limit of detection (LOD) was estimated 101 as three times the standard deviation of the background measurement. The sex of each 102 animal was determined and their live mass recorded. 103Freshly excreted faecal samples were collected directly from animals for subsequent 104 microbiome analysis. We sampled striped field mice (Apodemus agrarius; n = 29), yellow-105 necked mice (Apodemus flavicollis; n = 58), wood mice (Apodemus sylvaticus; n = 27) and 106 bank voles (Myodes glareolus; n = 22; Table S1). Faecal samples were immediately placed 107 into vials containing 100% ethanol and subsequently stored at -20°C. Samples were 108 transported under licence to the University of Salford (UK); sample integrity was maintained 109 during transit using dry ice and the samples were then stored at -20°C prior to DNA 110 extraction. We used fur clipping to mark each small mammal prior to release at the point of 111 capture, which allowed us to check whether each capture over the subsequent days was a 112 new animal. Only faeces from new animal captures were included in this study.113 114 Field sampling across the CEZ (2018) 115 Small mammals were trapped in July/August 2018 over 10 consecutive days, with only bank 116 voles included in this study. Twelve transects of Sherman traps were established at sites 117 across a gradient of ambient dose rates (Figure 1). Each transect measured 290 m with a 118 trap interval of 10 m (30 traps per transect). The 2018 sampling adopted the same protocol 119 for baiting and collection of captured animals that was used in 2017. For some of the 120 analyses, bank voles from 2018 have been categorised by collection 'site category', defined 121 as inside or outside of the Red Forest.122 Captured animals were transferred to the Chernobyl field station, where each animal 123 was live monitored to quantify the whole-body activity concentrations of both 137 Cs and 90...

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.