Frequency distributions of 90Sr and 137Cs concentrations in an ecosystem of the "Red Forest" area in the Chernobyl exclusion zone

Investigation of Radionuclide Migration at Sites Adjacent to the 30-km Exclusion Zone of the Chernobyl Nuclear Power Plant

ABSTRACT

This paper reports the study of the vertical migration of radionuclides in soils at test sites adjacent to the 30-km Chernobyl Exclusion Zone. The results of this effort demonstrate that the migration processes for studied pollution occur similarly to the fuel fallout behavior at the vicinity of the Chernobyl Nuclear Power Plant (ChNPP) Unit 4. It was also observed that the main fallout component, 137Cs, originated from aerosol fallout and was bound in the surface layer. The authors determined a significant increase of 60Co, 94Nb, and 241Am radionuclide concentrations in soils near the ChNPP Unit 4 and suggested their appearance due to the installation of the New Safe Confinement. Niobium-94 activity is proposed as a marker for monitoring the "fresh" fallout in the Chernobyl Exclusion Zone.

Current ionising radiation doses in the Chernobyl Exclusion Zone do not directly impact on soil biological activity

Although soil organisms are essential for ecosystem function, the impacts of radiation on soil biological activity at highly contaminated sites has been relatively poorly studied. In April-May 2016, we conducted the first largescale deployment of bait lamina to estimate soil organism (largely soil invertebrate) feeding activity in situ at study plots in the Chernobyl Exclusion Zone (CEZ). Across our 53 study plots, estimated weighted absorbed dose rates to soil organisms ranged from 0.7 μGy h^-1 to 1753 μGy h^-1. There was no significant relationship between soil organism feeding activity and estimated weighted absorbed dose rate. Soil biological activity did show significant relationships with soil moisture content, bulk density (used as a proxy for soil organic matter) and pH. At plots in the Red Forest (an area of coniferous plantation where trees died because of high radiation exposure in 1986) soil biological activity was low compared to plots elsewhere in the CEZ. It is possible that the lower biological activity observed in the Red Forest is a residual consequence of what was in effect an acute high exposure to radiation in 1986.

Radiation-induced effects on bone marrow of bank voles inhabiting the Chornobyl exclusion zone

PURPOSE

To investigate the effects of chronic exposure to low-dose radiation on bone marrow hematopoiesis of bank voles inhabiting the radioactively contaminated territory of the Chornobyl exclusion zone.

MATERIALS AND METHODS

Animals were collected within the highly radioactive area of the so-called Red Forest located close to the destroyed 4th reactor of the Chornobyl Nuclear Power Plant. Radioecological investigations included evaluation of radiocontamination of soil samples by ⁹⁰Sr and ¹³⁷Cs, levels of incorporated radionuclides in animals' bodies and organs, as well as the absorbed dose rates. The study of peripheral blood and bone marrow parameters combined with cytogenetic analysis of bone marrow micronucleated polychromatic erythrocytes and standard metaphase test was carried out.

RESULTS

The blood system of the exposed animals manifested significant changes in peripheral blood parameters (anaemia and leucocyte formula left shift), ineffective differentiation and maturation of bone marrow cells, particularly relevant to the erythroid and granulocyte pools. Increased yields of bone marrow micronucleated polychromatic erythrocytes and chromosomal aberrations, including dicentrics and Robertsonian fusion-like configurations, were revealed.

CONCLUSIONS

Observed disturbances in the bone marrow and peripheral blood suggest functional instability and inefficient compensatory and recovery reactions of the blood system of the bank voles from the contaminated areas of the Chornobyl exclusion zone. We assume that they are the consequences both of direct radiation exposure and hereditary pathological changes that have formed in a number of generations inhabiting radioactively contaminated areas.

Spectroscopy of Radiostrontium in Fuel Materials Retrieved from the Chernobyl Nuclear Power Plant

ABSTRACT

Some basic methods of measuring radiostrontium activity by spectroscopic methods are considered in this study. These methods of assessing beta spectra and the characteristic radiation that accompanies the breakdown of radiostrontium are described. The sensitivity of these methods based on the assessments of beta spectra both after radiochemical procedures and without radiochemistry is presented. The objective of this paper is to review the spectroscopic procedures that have been developed and used to determine radiostrontium in various matrices; they are focused on modern methods. Samples of fuel particles of different origins, obtained from the Chernobyl Nuclear Power Plant Unit 4, were analyzed using the methods presented in this study.

Review of resistance to chronic ionizing radiation exposure under environmental conditions in multicellular organisms

Ionizing radiation resistance occurs among many phylogenetic groups and its mechanisms remain incompletely understood. Tolerances to acute and chronic irradiation do not always correlate because different mechanisms may be involved. The radioresistance phenomenon becomes even more complex in the field than in the laboratory because the effects of radioactive contamination on natural populations are intertwined with those of other factors, such as bioaccumulation of radionuclides, interspecific competition, seasonal variations in environmental conditions, and land use changes due to evacuation of humans from contaminated areas. Previous reviews of studies performed in radioactive sites like the Kyshtym, Chernobyl, and Fukushima accident regions, and of protracted irradiation experiments, often focused on detecting radiation effects at low doses in radiosensitive organisms. Here we review the literature with a different purpose: to identify organisms with high tolerance to chronic irradiation under environmental conditions, which maintained abundant populations and/or outcompeted more radiosensitive species at high dose rates. Taxa for which consistent evidence for radioresistance came from multiple studies conducted in different locations and at different times were found among plants (e.g. willow and birch trees, sedges), invertebrate and vertebrate animals (e.g. rotifers, some insects, crustaceans and freshwater fish). These organisms are not specialized "extremophiles", but tend to tolerate broad ranges of environmental conditions and stresses, have small genomes, reproduce quickly and/or disperse effectively over long distances. Based on these findings, resistance to radioactive contamination can be examined in a more broad context of chronic stress responses.

Radionuclide transfer to wildlife at a 'Reference site' in the Chernobyl Exclusion Zone and resultant radiation exposures

This study addresses a significant data deficiency in the developing environmental protection framework of the International Commission on Radiological Protection, namely a lack of radionuclide transfer data for some of the Reference Animals and Plants (RAPs). It is also the first study that has sampled such a wide range of species (invertebrates, plants, amphibians and small mammals) from a single terrestrial site in the Chernobyl Exclusion Zone (CEZ). Samples were collected in 2014 from the 0.4 km² sampling site, located 5 km west of the Chernobyl Nuclear Power complex. We report radionuclide (¹³⁷Cs, ⁹⁰Sr, ²⁴¹Am and Pu-isotopes) and stable element concentrations in wildlife and soil samples and use these to determine whole organism-soil concentration ratios and absorbed dose rates. Increasingly, stable element analyses are used to provide transfer parameters for radiological models. The study described here found that for both Cs and Sr the transfer of the stable element tended to be lower than that of the radionuclide; this is the first time that this has been demonstrated for Sr, though it is in agreement with limited evidence previously reported for Cs. Studies reporting radiation effects on wildlife in the CEZ generally relate observations to ambient dose rates determined using handheld dose meters. For the first time, we demonstrate that ambient dose rates may underestimate the actual dose rate for some organisms by more than an order of magnitude. When reporting effects studies from the CEZ, it has previously been suggested that the area has comparatively low natural background dose rates. However, on the basis of data reported here, dose rates to wildlife from natural background radionuclides within the CEZ are similar to those in many areas of Europe.

Inter-cultivar variation in soil-to-plant transfer of radiocaesium and radiostrontium in Brassica oleracea

Radiocaesium and radiostrontium enter the human food chain primarily via soil-plant transfer. However, uptake of these radionuclides can differ significantly within species (between cultivars). The aim of this study was to assess inter-cultivar variation in soil-to-plant transfer of radiocaesium and radiostrontium in a leafy crop species, Brassica oleracea. This study comprised four independent experiments: two pot experiments in a controlled environment artificially contaminated with radiocaesium, and two field experiments in an area contaminated with radiocaesium and radiostrontium in the Chernobyl Exclusion Zone. Radiocaesium concentration ratios varied 35-fold among 27 cultivars grown in pots in a controlled environment. These 27 cultivars were then grown with a further 44 and 43 other cultivars in the Chernobyl Exclusion Zone in 2003 and 2004, respectively. In the field-grown cultivars radiocaesium concentration ratios varied by up to 35-fold and radiostrontium concentration ratios varied by up to 23-fold. In three of these experiments (one pot experiment, two field experiments) one out of the 27 cultivars was found to have a consistently lower radiocaesium concentration ratio than the other cultivars. The two field experiments showed that, five out of the 66 cultivars common to both experiments had consistently lower radiocaesium concentration ratios, and two cultivars had consistently lower radiostrontium concentration ratios. One cultivar had consistently lower radiocaesium and radiostrontium concentration ratios. The identification of cultivars that have consistently lower radiocaesium and/or radiostrontium concentration ratios suggests that cultivar selection or substitution may be an effective remediation strategy in radiologically contaminated areas. Future research should focus on plant species that are known to be the largest contributors to human dose.

Comparison of the Chernobyl and Fukushima nuclear accidents: a review of the environmental impacts

The environmental impacts of the nuclear accidents of Chernobyl and Fukushima are compared. In almost every respect, the consequences of the Chernobyl accident clearly exceeded those of the Fukushima accident. In both accidents, most of the radioactivity released was due to volatile radionuclides (noble gases, iodine, cesium, tellurium). However, the amount of refractory elements (including actinides) emitted in the course of the Chernobyl accident was approximately four orders of magnitude higher than during the Fukushima accident. For Chernobyl, a total release of 5,300 PBq (excluding noble gases) has been established as the most cited source term. For Fukushima, we estimated a total source term of 520 (340-800) PBq. In the course of the Fukushima accident, the majority of the radionuclides (more than 80%) was transported offshore and deposited in the Pacific Ocean. Monitoring campaigns after both accidents reveal that the environmental impact of the Chernobyl accident was much greater than of the Fukushima accident. Both the highly contaminated areas and the evacuated areas are smaller around Fukushima and the projected health effects in Japan are significantly lower than after the Chernobyl accident. This is mainly due to the fact that food safety campaigns and evacuations worked quickly and efficiently after the Fukushima accident. In contrast to Chernobyl, no fatalities due to acute radiation effects occurred in Fukushima.

Are radiosensitivity data derived from natural field conditions consistent with data from controlled exposures? A case study of Chernobyl wildlife chronically exposed to low dose rates

The discrepancy between laboratory or controlled conditions ecotoxicity tests and field data on wildlife chronically exposed to ionising radiation is presented for the first time. We reviewed the available chronic radiotoxicity data acquired in contaminated fields and used a statistical methodology to support the comparison with knowledge on inter-species variation of sensitivity to controlled external γ irradiation. We focus on the Chernobyl Exclusion Zone and effects data on terrestrial wildlife reported in the literature corresponding to chronic dose rate exposure situations (from background ~100 nGy/h up to ~10 mGy/h). When needed, we reconstructed the dose rate to organisms and obtained consistent unbiased data sets necessary to establish the dose rate-effect relationship for a number of different species and endpoints. Then, we compared the range of variation of radiosensitivity of species from the Chernobyl-Exclusion Zone with the statistical distribution established for terrestrial species chronically exposed to purely gamma external irradiation (or chronic Species radioSensitivity Distribution - SSD). We found that the best estimate of the median value (HDR50) of the distribution established for field conditions at Chernobyl (about 100 μGy/h) was eight times lower than the one from controlled experiments (about 850 μGy/h), suggesting that organisms in their natural environmental were more sensitive to radiation. This first comparison highlights the lack of mechanistic understanding and the potential confusion coming from sampling strategies in the field. To confirm the apparent higher sensitive of wildlife in the Chernobyl Exclusion Zone, we call for more a robust strategy in field, with adequate design to deal with confounding factors.