Assessing radiation exposure of herbaceous plant species at the East-Ural Radioactive Trace

Investigation of biological-rhythm patterns: physiological and biochemical effects in herbaceous plants exposed to low-level chronic radiation - part 1: nonirradiated seeds

HYPOTHESIS

Because reactive oxygen species are involved in the regulation of biological rhythms, we hypothesized that intra-annual variability of seed progeny quality at low doses of ionizing radiation (LDIRs) would differ from that of background plants.

MATERIALS AND METHODS

We conducted 12 consecutive experiments using the roll culture method by germinating seeds (monthly for 3 weeks) of six herbaceous plant species (Bromus inermis, Geum aleppicum, Plantago major, Rumex confertus, Silene latifolia, and Taraxacum officinale) growing under conditions of chronic radiation in the East Ural Radioactive Trace (EURT). We assessed physiological (seed viability and abnormality frequency) and biochemical (low-molecular-weight antioxidants, LMWAs) parameters of seedlings.

RESULTS

Total absorbed dose rates of maternal plants (TADRplants) and seed embryos (TADRseeds) in the EURT exceeded background levels by 1-3 and 1-2 orders of magnitude, respectively. Nonlinear dependencies on TADR were mainly characteristic of physiological and biochemical parameters. For most populations of the studied species (B. inermis, G. aleppicum, R. confertus, and S. latifolia), seedling survival and root length decreased in the autumn-winter period, while the frequency of abnormal seedlings increased. The content of LMWAs could be ranked as R. confertus > B. inermis > G. aleppicum > S. latifolia, in good agreement with the presence of anthocyanin pigmentation in the plants. The lowest synthesis of antioxidants in seedlings was observed in winter. A high LMWA content promoted growth and reduced the frequency of abnormal seedlings.

CONCLUSIONS

These results underscore a multistage nature of the impact of LDIRs on intra-annual biological rhythms in plants. High heterogeneity in reference group 'wild grasses' and diversity of their radiobiological effects should help to develop methods of radiation protection for natural ecosystems and facilitate approaches used by the International Commission on Radiological Protection.HighlightsAbsorbed dose rates for six plant species in the East Ural Radioactive Trace (EURT) area range from 0.11 to 73.89 µGy h-s (plants) and 0.11 to 6.88 µGy h-s (seed embryos).Intra-annual rhythms of physiological and biochemical parameters in the EURT zone differ from those in background seedlings.Plants in the EURT area exhibit a wide range of trait variability, asynchrony of the manifestation of the effects, nonlinear dose-response relations, and hormesis.A high content of low-molecular-weight antioxidants (LMWAs) is associated with low frequency of developmental abnormalities and high viability of seed progeny.

Transposable Elements in the Revealing of Polymorphism-Based Differences in the Seeds of Flax Varieties Grown in Remediated Chernobyl Area

The nuclear reactor accident in Chernobyl, Ukraine, resulted in effects both locally and farther away. Most of the contaminated areas were the agricultural fields and forests. Experimental fields were established near Chernobyl—radioactively contaminated fields localized 5 km from Chernobyl Nuclear Power Plant as well as the remediated soil that is localized directly in the Chernobyl town. Two flax varieties growing under chronic exposition to ionizing radiation were used for this study—the local Ukrainian variety Kyivskyi and a commercial variety Bethune. The screening of the length polymorphism generated by transposable elements insertions were performed. All known types of common flax transposon, retrotransposons and iPBS approach were used. In the iPBS multiplex analyze, for the Kyivskyi variety, a unique addition was found in the seeds from the radioactive contaminated field and for the Bethune variety, a total of five amplicon additions were obtained and one deletion. For the TRIM Cassandra fingerprints, two amplicon additions were generated in the seeds from radioactive contaminated fields for the Bethune variety. In summary, the obtained data represent the genetic diversity between control and irradiated subgroups of flax seeds from Chernobyl area and the presence of activated transposable elements due to the irradiation stress.

Evaluation of the genetic structure of Bromus inermis populations from chemically and radioactively polluted areas using microsatellite markers from closely related species

Hypothesis The ecotoxicological and radiobiological effects can be manifested in a decrease in genetic diversity with an increase in toxic and radiation load, in an increase in the frequencies of rare and/or unique (private) alleles in impact samples, and in a decrease in the differentiation of B. inermis populations within each pollution area.Materials and methods We have selected a collection of primers for Bromus inermis, consisting of 21 microsatellite (SSR) loci from B. sterilis, B. tectorum and Triticum aestivum. The level of toxic load (chemically polluted area) was 4-19 conventional units, and the absorbed dose rate (the Kyshtym accident area) varied from 0.153 to 21.5 μGy h^-1, which is up to two orders higher than the natural background radiation level (≈ 0.1 μGy h^-1).Results Only eight of 21 (38%) of SSR primers showed good transferability and were used for B. inermis population studies from areas of technogenic pollution (heavy metals and radionuclides). We revealed 42 alleles at eight loci, and the number of alleles per locus varied from one to 13 in B. inermis populations. The percentage of polymorphic loci in B. inermis populations was 48.44%, the polymorphism information content (PIC) value was 0.556, and Shannon information index was 0.69 ± 0.3. A total of 22 rare, 14 private and 9 both rare and private alleles were reported for all B. inermis populations. There were no correlations between geographic and genetic distances. Only 6.8% of the genetic variability was distributed among B. inermis populations.Conclusion There was no decrease in genetic diversity ("genetic erosion") found in B. inermis populations growing for a long time under anthropogenic stress. No significant differences in the number of rare and private alleles in the background and impact populations of B. inermis were found. The smooth brome is characterized by low differentiation of the populations. Possible reasons for this phenomenon are discussed.

Radiological risk assessment in the terrestrial ecosystem: comparative study of two software tools used for dose rate calculations

In this study, two software tools, namely the ERICA Assessment Tool and the RESRAD-BIOTA code, are used for the calculation of the radiological exposure of non-human organisms. For the purposes of the analysis, data retrieved from field studies are used. The site-specific measurements were performed on organisms (mammals-sheep and goats of Bovidae spp.) collected from free-ranged grazing regions in Greece. Plants (grass) of Poaceae spp. and soil samples were also collected from these regions. Natural radionuclides (²²⁶Ra, ²²⁸Ra, and ²²⁸Th) of lithogenic origin and ¹³⁷Cs, resulted from human activities (Chernobyl and Fukushima nuclear power plant accidents and global fallout), were detected in all samples. The measured activity concentrations were used as input to the two software tools, the ERICA Assessment Tool and the RESRAD-BIOTA code. The results of the simulations provided the external, internal, and total dose rates received by the organisms due to the exposure to the radionuclides. The assessments indicated that out of all detected radionuclides, ²²⁸Th is the main contributor to the external dose and ²²⁶Ra and ²²⁸Ra are the main contributors to the internal dose. The comparative analysis of the two tools revealed significant differences in the calculated doses. In fact, external and internal doses calculated by RESRAD-BIOTA are higher than the values calculated by the ERICA Tool, due to the dose conversion coefficients (DCCs) used for the dose calculation. RESRAD-BIOTA provides more conservative values, but ERICA Tool provides lower uncertainty due to the higher flexibility in the design of the phantom organism. On a risk assessment basis, there is no significant impact, due to organisms' exposure to radioactivity. However, further consideration of the exposure levels is required due to the potential effects of protracted low-level ionizing radiation on the various levels of life's organization.

Heterogeneity of 90Sr radioactive contamination at the head part of the East Ural radioactive trace (EURT)

1: We measured ⁹⁰Sr concentrations and beta particle flux density (BPFD) in 44 soil samples collected from four soil profiles across a central transect on the head of the East Ural Radioactive Trace (EURT). The relationship between BPFD and ⁹⁰Sr concentration of each soil sample can be characterised by a linear regression model; ⁹⁰Sr concentration in the upper 12 cm soil layer can thus be assessed by measuring BPFD in the soil surface. 2: The BPFD on the soil surface was measured at 969 points at seven sites with linear dimensions ranging from 140 × 20 m to 140 × 320 m. The correspondence of ⁹⁰Sr concentration in the 12 cm soil layer with its BPFD value was calculated for each of these seven sites. Eighty (80) % of ⁹⁰Sr concentration measurements in the 12 cm soil layer in each model site differed by a factor of 2.0-5. The variability of ⁹⁰Sr concentration increased significantly in the 12 cm upper soil layer over territories with visual features of landscape disturbance (pits, trenches). The ratio of maximum to minimum concentration of ⁹⁰Sr varied from 6.1 to 6.6 in the 12 cm soil layer over territories without visual features of anthropogenic soil disturbance. 3: The ⁹⁰Sr concentration was measured in the skeletons of 34 juvenile Microtus oeconomus individuals weighing less than 12.5 g and trapped at the four model sites in July. The assessment of ⁹⁰Sr concentration in the 12 cm soil layer was conducted for each point where an animal was trapped. The relationship between ⁹⁰Sr concentration in soil and in the skeleton was characterised by a linear regression model with a determination coefficient of 0.51. 4: The concentration ratio for ⁹⁰Sr from soil to skeleton (CR_{skeleton-soil}) was 2.0 ± 0.1 for M. oeconomus over the territory of the EURT, which is consistent with the minimum value of the same CR_{skeleton-soil} for M. oeconomus from the Chernobyl area (Chesser et al., 2000).

Genetic variation in natural Melandrium album populations exposed to chronic ionizing radiation

The effect of radiation pollution on genetic variation in natural populations of Melandrium album was investigated at the head part of the East-Ural Radioactive Trace (EURT) and background areas. The highest genetic differentiation estimated using F _ST was revealed between compared pairs of the background and impact samples in populations of M. album. The highest rate of polymorphism was observed at the closest to nuclear accident, Impact-1 site. The unique alleles (Mdh-3¹⁰⁴, Pgi-2¹⁰⁶, Lap ¹⁰⁵, Mdh-2⁹⁶, and Dia ⁹⁴) were discovered at the EURT. Individuals from chronically low-level irradiated sites were genetically closer than to plants from background sites using Nadhdh locus. The increase of the frequency of unique homozygous and heterozygous genotypes was identified in populations of M. album growing under chronic radiation exposure conditions. The largest contribution to the group of unique heterozygous genotypes at the EURT was made by three loci - Lap, Pgi-2, and Nadhdh; the main role in interpopulation differentiation of samples was made by the alleles Sod-2¹¹⁵, Skdh ¹⁰⁰, and Nadhdh ¹⁰⁰. Our results provide evidence for the correlation between the increase of genetic variation other than the «genetic erosion» and chronic radiation exposure factor in natural plant populations.

Radioactivity measurements and dose rate calculations using ERICA tool in the terrestrial environment of Greece

In the present study, the radioactivity levels to which terrestrial non-human biota were exposed are examined. Organisms (grass and herbivore mammals) and abiotic components (soil) were collected during the period of 2010 to 2014 from grasslands where sheep and goats were free-range grazing. Natural background radionuclides ((226)Ra, (228)Ra, (228)Th) and artificial radionuclides ((137)Cs, (134)Cs, (131)I) were detected in the collected samples using gamma spectrometry. The actual measured activity concentrations and site-specific data of the studied organisms were imported in ERICA Assessment Tool (version 1.2.0) in order to provide an insight of the radiological dose rates. The highest activity concentrations were detected in samples collected from Lesvos island and the lowest in samples collected from Attiki and Etoloakarnania prefectures. The highest contribution to the total dose rate was clearly derived from the internal exposure and is closely related to the exposure to alpha emitters of natural background ((226)Ra and (228)Th). The Fukushima-derived traces of (137)Cs, (134)Cs, and (131)I, along with the residual (137)Cs, resulted in quite low contribution to the total dose rate. The obtained results may strengthen the adaptation of software tools to a wider range of ecosystems and may be proved useful in further research regarding the possible impact of protracted low level ionizing radiation on non-human biota. This kind of studies may contribute to the effective incorporation of dosimetry tools in the development of integrated environmental and radiological impact assessment policies.

Current assessment of integrated content of long-lived radionuclides in soils of the head part of the East Ural Radioactive Trace

Based on the datasets obtained during investigations from 2003 to 2012, the spatial distributions of (90)Sr, (137)Cs, and (239,240)Pu content in the soils of the head part of the East Ural Radioactive Trace (EURT) were mapped using the geographic information system ArcGIS. Taking into account the presence of spatial autocorrelation and anisotropy in the source data, an ordinary kriging method was applied to interpolate values of radionuclide contamination density at unsampled places. Further geostatistical data analysis was performed to determine the basic parameters of spatial dependencies and to integrally assess the contamination by long-lived radionuclides in soils of the central, east peripheral, and west peripheral parts of the trace. This analysis was based on simplified geometric models (sector- and rectangle-shaped areas). The Monte Carlo method was used to quantitatively assess the uncertainty of the values for the integrated quantities resulting from the statistical errors of the source data approximation.

Contemporary radiation doses to murine rodents inhabiting the most contaminated part of the EURT

The contemporary radiation doses to the organs and tissues of murine rodents inhabiting the most contaminated part of the EURT were estimated. The bones of animals trapped in 2005 at territories with a surface (90)Sr contamination of 24-40 MBq/m(2) were used for dose reconstruction. The concentration of (90)Sr in the animals' skulls was measured using the nondestructive method of bone radiometry. The dose estimation procedure included application of the published values of absorbed fractions of beta-radiation energy for different combinations of source and target organs, accounting for the distribution of radionuclide by organs and tissues. Twelve conversion coefficients were obtained to link the skeleton (90)Sr concentration and doses to eleven organs and the whole body. The whole-body dose rate on the 45th day after the beginning of exposure normalised to whole-body activity is 0.015 (mGy day(-1))/(Bq g(-1)). The estimation yields the following values of doses for Microtus agrestis, Sylvaemus uralensis and Clethrionomys rutilus, respectively: maximum absorbed doses in the skeleton: 267, 121 and 160 mGy; mean whole body internal doses: 37, 14 and 23 mGy; mean internal dose rates on the last day before trapping: 1.2; 0.44 and 0.75 mGy/day. Approaches to the assessment of doses to foetuses and to offspring before weaning were also developed.