Chapter III. Consequences of the Chernobyl Catastrophe for the Environment

Strontium-90 pollution can be bioremediated with the green microalga Tetraselmis chui

Strontium-90 (90Sr) is an artificial radioisotope produced by nuclear fission, with a relatively long half-life of 29 years. This radionuclide is released into the environment in the event of a nuclear incident, posing a serious risk to human and ecosystem health. There is a need to develop new efficient methods for the remediation of 90Sr, as current techniques for its removal have significant technical limitations and involve high energy and economic costs. Recently, several species of green microalgae within the class Chlorodendrophyceae have been found to form intracellular mineral inclusions of amorphous calcium carbonate (ACC), which can be highly enriched in natural (non-radiogenic) Sr. As bioremediation techniques are an attractive option to address radioactive pollution, we investigated the capacity of the unicellular alga Tetraselmis chui (class Chlorodendrophyceae) to sequester 90Sr. The 90Sr uptake capacity of T. chui cells was assessed in laboratory cultures by monitoring the time course of radioactivity in the culture medium using liquid scintillation counting (LSC). T. chui was shown to effectively sequester 90Sr, reducing the initial radioactivity of the culture medium by up to 50%. Thus, this study demonstrates the potential of the microalga T. chui to be used as a bioremediation agent against 90Sr pollution.

The occurrence of 40K and 137Cs radioactivity in mosses during 2015-2019 in the Djerdap National Park (E. Serbia)

The radiation status of the national park (NP) Djerdap (Eastern Serbia) is characterized using bioindicators (mosses). Mosses (16 species, 156 samples) were collected randomly within the area of NP Djerdap during the month of June, periodically from 2015 to 2019. Samples were collected in the regions of Dobra, Donji Milanovac, and Tekija. Within the mosses, the presence of ⁴⁰ K and ¹³⁷Cs is regarded as a good indicator of radionuclides present in the environment due to their easy interchangeability with ³⁹ K highly present in living moss organisms. The activity concentrations of gamma ray-emmiting radionuclides in samples were determined using high-resolution gamma ray spectrometry, an HPGe-ORTEC/Ametek detector. The determining activity concentrations of ⁴⁰ K and ¹³⁷Cs in collected samples were as follows: for ⁴⁰ K from 31.4 to 721 Bq kg^-1and for ¹³⁷Cs varied from 2.6 to 908 Bq kg^-1. The average activity concentrations of ⁴⁰ K and ¹³⁷Cs (Bq kg^-1) in mosses in the period 2015-2019 were the lowest in moss samples collected in the Dobra region, and the highest in the area of Donji Milanovac. The most prevalent collected moss species within the Djerdap National Park was Hypnum cupressiforme. The determined activity concentrations in H. cupressiforme of ¹³⁷Cs for the whole region of NP Djerdap for all 5 years was 78.1 ± 70.3 Bq kg^-1 and of ⁴⁰ K was 181 ± 86.1 Bq kg^-1.

Ionizing radiation and melanism in Chornobyl tree frogs

Human actions are altering ecosystems worldwide. Among human‐released pollutants, ionizing radiation arises as a rare but potentially devastating threat to natural systems. The Chornobyl accident (1986) represents the largest release of radioactive material to the environment. Our aim was to examine how exposure to radiation from the Chornobyl accident influences dorsal skin coloration of Eastern tree frog (Hyla orientalis) males sampled across a wide gradient of radioactive contamination in northern Ukraine. We assessed the relationship between skin frog coloration (which can act as a protective mechanism against ionizing radiation), radiation conditions and oxidative stress levels. Skin coloration was darker in localities closest to areas with high radiation levels at the time of the accident, whereas current radiation levels seemed not to influence skin coloration in Chornobyl tree frogs. Tree frogs living within the Chornobyl Exclusion Zone had a remarkably darker dorsal skin coloration than frogs from outside the Zone. The maintenance of dark skin coloration was not linked to physiological costs in terms of frog body condition or oxidative status, and we did not detect short‐term changes in frog coloration. Dark coloration is known to protect against different sources of radiation by neutralizing free radicals and reducing DNA damage, and, particularly melanin pigmentation has been proposed as a buffering mechanism against ionizing radiation. Our results suggest that exposure to high levels of ionizing radiation, likely at the time of the accident, may have been selected for darker coloration in Chornobyl tree frogs. Further studies are needed to determine the underlying mechanisms and evolutionary consequences of the patterns found here.

Ionizing Radiation-Induced Brain Cell Aging and the Potential Underlying Molecular Mechanisms

Population aging is occurring rapidly worldwide, challenging the global economy and healthcare services. Brain aging is a significant contributor to various age-related neurological and neuropsychological disorders, including Alzheimer's disease and Parkinson's disease. Several extrinsic factors, such as exposure to ionizing radiation, can accelerate senescence. Multiple human and animal studies have reported that exposure to ionizing radiation can have varied effects on organ aging and lead to the prolongation or shortening of life span depending on the radiation dose or dose rate. This paper reviews the effects of radiation on the aging of different types of brain cells, including neurons, microglia, astrocytes, and cerebral endothelial cells. Further, the relevant molecular mechanisms are discussed. Overall, this review highlights how radiation-induced senescence in different cell types may lead to brain aging, which could result in the development of various neurological and neuropsychological disorders. Therefore, treatment targeting radiation-induced oxidative stress and neuroinflammation may prevent radiation-induced brain aging and the neurological and neuropsychological disorders it may cause.

Difference of ecological half-life and transfer coefficient in aquatic invertebrates between high and low radiocesium contaminated streams

The Fukushima accident emitted radioactive substances into the environment, contaminating litter, algae, sand substrate, aquatic invertebrates, and fish in freshwater streams. Because these substances have substantial effects on stream ecology over many years, it is necessary to clarify the diffusion and decay mechanisms of radiocesium. The transfer coefficient differed among aquatic invertebrate groups, likely due to the differences in habitat. The ecological half-life of cesium was longer where the air dose rate was lower. The transfer coefficient was also higher in areas with lower air dose rate. The radiocesium concentration in algae was inversely related to stream current velocity in the radiocesium-contaminated area. However, this relationship was not observed in the lower air dose rate area: the radiocesium concentration in algae in the rapid-velocity areas tended to be higher than that in the slow-velocity areas. This reverse trend would lead to a longer period of freshwater contamination. The radiocesium concentration would continue to decrease in highly contaminated areas, but it would be difficult to reduce the radiocesium concentration in less-contaminated areas because different contamination mechanisms are at work. Controlling the water flow is key to regulating radiocesium concentration in freshwater ecosystems.

Borrelia and Other Zoonotic Pathogens in Ixodes ricinus and Dermacentor reticulatus Ticks Collected from the Chernobyl Exclusion Zone on the 30th Anniversary of the Nuclear Disaster

Background: The 26th of April 2016 marked 30 years since the Chernobyl accident has occurred in Ukraine. As a result, the uninhabited Chernobyl region has been directly exposed to ionizing radiation for >30 years. Most work has focused on identifying associations between levels of radiation and the abundance, distribution, and mutation rates of plants and animals. Much less, however, is known about microbial communities in this affected region. To date, there are no reports on the prevalence of any tick-borne pathogens in Ixodes ricinus ticks from the Chernobyl exclusion zone (CEZ). The objective of our study was to examine the abundance of I. ricinus and Dermacentor reticulatus ticks in the CEZ and to investigate the prevalence of Borrelia burgdorferi sensu lato (s.l.) and other zoonotic agents in these ixodid ticks. Methods: A total of 260 questing I. ricinus and 100 D. reticulatus adult ticks were individually polymerase chain reaction analyzed for the presence of Anaplasma phagocytophilum, Babesia spp., Bartonella spp., Borrelia burgdorferi s.l., Francisella tularensis, and/or Rickettsia spp. Results: The respective infections rates were identified and compared with those of ixodid ticks that were concurrently collected from Kyiv. The significant differences between the infection rates of the CEZ and Kyiv ticks were observed for Rickettsia raoultii in D. reticulatus ticks (53.0% vs. 35.7%, respectively; p < 0.05) and Bartonella spp. (8.1% vs. 2.7%; P < 0.05) in I. ricinus ticks. Conclusions: Although the current data clearly demonstrated that the prevalence of some zoonotic pathogens were significantly higher in the ixodid ticks from the CEZ, a more comprehensive systematic approach is required to examine the causal effect of long-term ionizing radiation on adaptive changes of tick-borne pathogens.

Fibroblasts from bank voles inhabiting Chernobyl have increased resistance against oxidative and DNA stresses

Background

Elevated levels of environmental ionizing radiation can be a selective pressure for wildlife by producing reactive oxygen species and DNA damage. However, the underlying molecular mechanisms that are affected are not known.

Results

We isolated skin fibroblasts from bank voles (Myodes glareolus) inhabiting the Chernobyl nuclear power plant accident site where background radiation levels are about 100 times greater than in uncontaminated areas. After a 10 Gy dose of gamma radiation fibroblasts from Chernobyl animals recovered faster than fibroblasts isolated from bank voles living in uncontaminated control area. The Chernobyl fibroblasts were able to sustain significantly higher doses of an oxidant and they had, on average, a higher total antioxidant capacity than the control fibroblasts. Furthermore, the Chernobyl fibroblasts were also significantly more resistant than the control fibroblasts to continuous exposure to three DNA damaging drugs. After drug treatment transcription of p53-target gene pro-apoptotic Bax was higher in the control than in the Chernobyl fibroblasts.

Conclusion

Fibroblasts isolated from bank voles inhabiting Chernobyl nuclear power plant accident site show elevated antioxidant levels, lower sensitivity to apoptosis, and increased resistance against oxidative and DNA stresses. These cellular qualities may help bank voles inhabiting Chernobyl to cope with environmental radioactivity.

Electronic supplementary material

The online version of this article (10.1186/s12860-018-0169-9) contains supplementary material, which is available to authorized users.

Frequencies of chromosomal inversions in Drosophila melanogaster in Fukushima after the nuclear power plant accident

In order to investigate genetic impact of a large amount of radionuclides released by the Fukushima Dai-ichi Nuclear Power Plant accident in 2011, we surveyed 2,304 haploid genomes of Drosophila melanogaster collected in three localities in Fukushima in 2012 and 2013 for chromosomal inversions. No unique inversion was found in 298 genomes in 2012 and only two in 2,006 genomes in 2013. The observed frequencies were even lower than the long-term average frequency of unique inversions in Japan. The common cosmopolitan inversions were also examined in Fukushima, Kyoto, and Iriomote (Okinawa) in 2012. Among three samples in Fukushima, the flies in Iizaka, where environmental radiation level was the highest, showed the lowest frequency of In(2L)t, but the highest frequency of In(3R)P, contrary to the expectation of decreasing of their frequencies in higher polluted areas. These results suggest that, at this level of genetic analysis, Fukushima populations of D. melanogaster would not have been negatively impacted following the release of radionuclides. Transposable P-element mobility was not likely to induce DNA damage solely or synergistically with radioactivity, because their transposition activity was totally repressed in the Fukushima strains. However, it should be noted that, because of limitations in access to the exclusion zone, we could only sample the populations in areas of relatively low radioactive contamination (0.39-0.63 μSv/h). Therefore, the present study is likely to be underpowered to detect any effects that might be expected in heavily contaminated areas.

Dietary supplementation with radionuclide free food improves children's health following community exposure to (137)Cesium: a prospective study

BACKGROUND

Following the Chernobyl nuclear disaster of 1986, vast areas of Ukraine became contaminated with radionuclides. We examined health effects of school-based food intervention for children in a rural region Narodichi, Ukraine, exposed to low-level radiation through diet of locally produced foods. Until 1995, children received three daily meals with low content of artificial radionuclides which were subsequently reduced to two.

METHODS

Annual health screening data (1993-1998) were examined using a quasi-experimental regression discontinuity analysis (n = 947 children; 3,573 repeated measurements). Generalized Estimating Equation models evaluated effect of the food supplementation reduction on hematologic measures and prevalence of anemia, acute respiratory illnesses and diseases of immune system.

RESULTS

Prior improvement of several hematologic parameters diminished after food supplementation was reduced. From 1995 to 1996, levels of hemoglobin and erythrocytes decreased from 12.63 (95% CI: 12.56-12.71) to 12.46 g/dL (% CI: 12.39-12.52) and from 4.10 (95% CI: 4.07-4.12) to 4.02 (95% CI: 4.00-4.04) × 10(12)/L, respectively. In agreement, the prevalence ratio (PR) of previously declining anemia increased from 0.57 to 1.31 per year (p(interaction )< .0001). The relation between food supplementation and hemoglobin levels was modified by residential (137)Cs soil levels. After food supply reduction, PR of common cold and bronchitis increased from 1.27 to 2.32 per year (p(interaction) = 0.01) and from 1.09 to 1.24 per year (p(interaction) = 0.43), respectively.

CONCLUSIONS

Food supplementation provided by the Ukrainian government likely prevented development of anemia in many of the children residing in the contaminated district. Food supplementation after the community exposure to radioactivity through a diet of locally grown foods should be considered as an effective approach to reduce adverse health effects of radiation.

Genotoxicity in earthworm after combined treatment of ionising radiation and mercury

This study was performed to investigate the acute genotoxic effects of mercury and radiation on earthworms (Eisenia fetida). The levels of DNA damage and the repair kinetics in the coelomocytes of E. fetida treated with mercuric chloride (HgCl₂) and ionising radiation (gamma rays) were analysed by means of the comet assay. For detection of DNA damage and repair, E. fetida was exposed to HgCl₂ (0-160 mg kg(-1)) and irradiated with gamma rays (0-50 Gy) in vivo. The increase in DNA damage depended on the concentration of mercury or dose of radiation. The results showed that the more the oxidative stress induced by mercury and radiation the longer the repair time that was required. When a combination of HgCl₂ and gamma rays was applied, the cell damage was much higher than those treated with HgCl₂ or radiation alone, which indicated that the genotoxic effects were increased after the combined treatment of mercury and radiation.