The biological effects of ionising radiation on Crustaceans: A review

Reproductive Capacity, but not Food Consumption, is Reduced by Continuous Exposure to Typical Genotoxic Stressor γ-Rays in the sentinel species Gammarus fossarum

The long-term impacts of radiocontaminants (and the associated risks) for ecosystems are still subject to vast societal and scientific debate while wildlife is chronically exposed to various sources and levels of either environmental or anthropogenic ionizing radiation from the use of nuclear energy. The present study aimed to assess induced phenotypical responses in both male and female gammarids after short-term continuous γ-irradiation, acting as a typical well-characterized genotoxic stressor that can interact directly with living matter. In particular, we started characterizing the effects using standardized measurements for biological effects on few biological functions for this species, especially feeding inhibition tests, molting, and reproductive ability, which have already been proven for chemical substances and are likely to be disturbed by ionizing radiation. The results show no significant differences in terms of the survival of organisms (males and females), of their short-term food consumption which is linked to the general health status (males and females), and of the molting cycle (females). In contrast, exposure significantly affected fecundity (number of embryos produced) at the highest dose rates for irradiated females (51 mGy h-1) and males (5 and 51 mGy h-1). These results showed that, in gammarids, reproduction, which is a critical endpoint for population dynamics, is the most radiosensitive phenotypic endpoint, with significant effects recorded on male reproductive capacity, which is more sensitive than in females. Environ Toxicol Chem 2024;43:2071-2079. © 2024 SETAC.

Evaluation of Cs-137 and natural radionuclides on different marine biota (crustacean and fishes) along Beheira governorate Coast-Egypt: RESRAD biota

PURPOSE

This work will focused on the environmental and radio-ecological impacts occurred on an Egyptian coastal region, based on the radiochemical measurement of 238U, 137Cs, 232Th, 40K. The novelty of the study was cleared by the using of new technique showing the integration of two biological RESRAD models, lead to a probabilistic estimation of the radionuclides bioaccumulation in different consumed marine organisms and determination the probability of human cancer risk at different ages.

MATERIAL AND METHODS

The 20 water samples were collected and mounted into clean containers, and their decay products, were measured in Bq.L-1, using different quality assurance tools. The study will used different statistical analysis and different RESRAD modeling codes were used in the study to predict the degree of environmental and radio-ecological impacts at the studied area, this will be helpful in order to define the impacts resulted from the transferring and accumulation of different radionuclides.

RESULTS

showed that the highest human dose conversion factor values of (5, 10, 15, with adult ages) were measured in Th-232 (mrem/pCi) while the lowest ingestion conversion factors values were observed in artificial 137Cs. On the other hand the highest values of external risk factor in case of (5, 10, 15 with adult age) were observed in artificial Cs-137(mrem/pCi), while the lowest value of external risk factor with the same ages were observed in U-238. This will lead to continual monitoring of artificial Cs-137 in different marine coastal regions. The arrangement of the bioaccumulation value (BIV) in Bq.kg-1 which being calculated by using RESRAD-Biota in case of crustacean animals will be as follow: U-238 > Th-232 > Cs-137, while the arrangement of BIV in case of fish animals will be: Cs-137 > U-232 > Th-232. On the other hand the arrangement of Internal Dose Conversion factors in case of crustacean animals will be: U-238 > Th-232 > Cs-137. While the arrangement of Internal Dose Conversion factors in case of fish animals will be: Cs-137> Th-232 > U-238.

CONCLUSION

RESRAD code's results showed that the arrangement of the bioaccumulation and Dose Conversion factors were depend on the type of marine living organism. RESRAD code also showed that there are increments of the calculated external risk factor values which resulted from the adult than all the infants (5,10 and 15 ages) ages this may be related to the continuous replacement of new human's body cells during the growth stages. The study results showed that, environmental bioaccumulation impacts of the artificial Cs-137 were very effective in both marine living organisms and human as this will support the relation between the ingestion Cs-137 in the body(inside the soft tissues), and the probability of the human cancer risk. On the other hand, study results showed the importance of using RESRAD BIOA code for the EIA's ecological and radiological studies which should be done for any future industrial coastal .projects.

Tritium: Its relevance, sources and impacts on non-human biota

Tritium (³H) is a radioactive isotope of hydrogen that is abundantly released from nuclear industries. It is extremely mobile in the environment and in all biological systems, representing an increasing concern for the health of both humans and non-human biota (NHB). The present review examines the sources and characteristics of tritium in the environment, and evaluates available information pertaining to its biological effects at different levels of biological organisation in NHB. Despite an increasing number of publications in the tritium radiobiology field, there exists a significant disparity between data available for the different taxonomic groups and species, and observations are heavily biased towards marine bivalves, fish and mammals (rodents). Further limitations relate to the scarcity of information in the field relative to the laboratory, and lack of studies that employ forms of tritium other than tritiated water (HTO). Within these constraints, different responses to HTO exposure, from molecular to behavioural, have been reported during early life stages, but the potential transgenerational effects are unclear. The application of rapidly developing "omics" techniques could help to fill these knowledge gaps and further elucidate the relationships between molecular and organismal level responses through the development of radiation specific adverse outcome pathways (AOPs). The use of a greater diversity of keystone species and exposures to multiple stressors, elucidating other novel effects (e.g., by-stander, germ-line, transgenerational and epigenetic effects) offers opportunities to improve environmental risk assessments for the radionuclide. These could be combined with artificial intelligence (AI) including machine learning (ML) and ecosystem-based approaches.

Multiomics Point of Departure (moPOD) Modeling Supports an Adverse Outcome Pathway Network for Ionizing Radiation

While adverse biological effects of acute high-dose ionizing radiation have been extensively investigated, knowledge on chronic low-dose effects is scarce. The aims of the present study were to identify hazards of low-dose ionizing radiation to Daphnia magna using multiomics dose-response modeling and to demonstrate the use of omics data to support an adverse outcome pathway (AOP) network development for ionizing radiation. Neonatal D. magna were exposed to γ radiation for 8 days. Transcriptomic analysis was performed after 4 and 8 days of exposure, whereas metabolomics and confirmative bioassays to support the omics analyses were conducted after 8 days of exposure. Benchmark doses (BMDs, 10% benchmark response) as points of departure (PODs) were estimated for both dose-responsive genes/metabolites and the enriched KEGG pathways. Relevant pathways derived using the BMD modeling and additional functional end points measured by the bioassays were overlaid with a previously published AOP network. The results showed that several molecular pathways were highly relevant to the known modes of action of γ radiation, including oxidative stress, DNA damage, mitochondrial dysfunction, protein degradation, and apoptosis. The functional assays showed increased oxidative stress and decreased mitochondrial membrane potential and ATP pool. Ranking of PODs at the pathway and functional levels showed that oxidative damage related functions had relatively low PODs, followed by DNA damage, energy metabolism, and apoptosis. These were supportive of causal events in the proposed AOP network. This approach yielded promising results and can potentially provide additional empirical evidence to support further AOP development for ionizing radiation.

Adverse outcome pathways (AOPs) for radiation-induced reproductive effects in environmental species: state of science and identification of a consensus AOP network

BACKGROUND

Reproductive effects of ionizing radiation in organisms have been observed under laboratory and field conditions. Such assessments often rely on associations between exposure and effects, and thus lacking a detailed mechanistic understanding of causality between effects occurring at different levels of biological organization. The Adverse Outcome Pathway (AOP), a conceptual knowledge framework to capture, organize, evaluate and visualize the scientific knowledge of relevant toxicological effects, has the potential to evaluate the causal relationships between molecular, cellular, individual, and population effects. This paper presents the first development of a set of consensus AOPs for reproductive effects of ionizing radiation in wildlife. This work was performed by a group of experts formed during a workshop organized jointly by the Multidisciplinary European Low Dose Initiative (MELODI) and the European Radioecology Alliance (ALLIANCE) associations to present the AOP approach and tools. The work presents a series of taxon-specific case studies that were used to identify relevant empirical evidence, identify common AOP components and propose a set of consensus AOPs that could be organized into an AOP network with broader taxonomic applicability.

CONCLUSION

Expert consultation led to the identification of key biological events and description of causal linkages between ionizing radiation, reproductive impairment and reduction in population fitness. The study characterized the knowledge domain of taxon-specific AOPs, identified knowledge gaps pertinent to reproductive-relevant AOP development and reflected on how AOPs could assist applications in radiation (radioecological) research, environmental health assessment, and radiological protection. Future advancement and consolidation of the AOPs is planned to include structured weight of evidence considerations, formalized review and critical assessment of the empirical evidence prior to formal submission and review by the OECD sponsored AOP development program.

Radiocaesium accumulation and fluctuating asymmetry in the Japanese mitten crab, Eriocheir japonica, along a gradient of radionuclide contamination at Fukushima

The 2011 Tohoku earthquake-tsunami and the subsequent nuclear accident at the Fukushima Dai-ichi Nuclear Power Station (FDNPS) led to large-scale radionuclide contamination of the marine and freshwater environment. Monitoring studies of marine food products in the Fukushima region have generally demonstrated a declining trend in radiocaesium concentrations. However, the accumulation and elimination of radiocaesium and potential biological effects remain poorly understood for freshwater biota inhabiting highly contaminated areas at Fukushima. Consequently, the present study aimed to assess radiocaesium accumulation and developmental effects on the commercially important catadromous Japanese mitten crab, Eriocheir japonica. E. japonica were collected from four sites along a gradient of radionuclide contamination 4-44 km in distance from the FDNPS in 2017. To determine potential developmental effects, fluctuating asymmetry (FA) was used as a measure of developmental stability. Combined ¹³⁴Cs and ¹³⁷Cs values for whole E. japonica from highly contaminated sites 4 and 16 km in distance from the FDNPS were 3040 ± 521 and 2250 ± 908 Bq kg^-1 wet weight respectively, 30 and 22 times greater than the Japanese standard limit of 100 Bq kg^-1. Estimated total dose rates based on radiocaesium concentrations in whole crabs and sediment ranged from 0.016 to 37.7 μGy h^-1. No significant relationship between radiocaesium accumulation and FA was recorded, suggesting that chronic radiation exposure at Fukushima is not inducing developmental effects in E. japonica as measured using fluctuating asymmetry. Furthermore, estimated dose rates were below proposed regulatory limits where significant deleterious effects are expected. The present study will aid in the understanding of the long-term consequences of radiation exposure for non-human biota and the management of radioactively contaminated environments.

The transcriptional landscape of the giant freshwater prawn: Embryonic development and early sexual differentiation mechanisms

The giant freshwater prawn pjMacrobrachium rosenbergii is one of the best studied species in aquaculture. However, the transcriptional changes associated with embryonic development and the sexual differentiation mechanism of M. rosenbergii remain to be elucidated. To characterize the embryonic development of this prawn and to determine whether differential expression and differential splicing play roles in the early sexual differentiation of M. rosenbergii, we profiled five developmental days of male and female embryos by RNA sequencing. We identified modules of co-expressed genes representing waves of transcription that correspond to physiological processes in early embryonic development (such as the maternal-to-zygotic transition) up to preparation for life outside the egg (development of muscles, cuticle etc.). Additionally, we found that hundreds of genes are differentially expressed between sexes, most of them uncharacterized, suggesting that the sex differentiation mechanism of M. rosenbergii might contain clade-specific elements. The resulting first-of-a-kind transcriptional map of embryonic development of male and female M. rosenbergii will guide future studies to reveal the roles of specific genes and splicing isoforms in the embryonic development and sexual differentiation process of M. rosenbergii.

Medium-term feasibility of the management of the invasive crayfish Procambarus clarkii with the sterile males release technique

BACKGROUND

The sterile male release technique (SMRT) is a useful method applied for controlling invasive and pest species. However, the use of X-rays can lead to negative effects on the survival and health conditions of sterilized males.

RESULTS

This study was set up to evaluate the functional integrity of physiological, morphological and behavioural responses in males of the red swamp crayfish, Procambarus clarkii (Girard, 1852), exposed to a dose of 40 Gy of ionizing radiation. Concerning physiological responses, the results showed that the irradiation dose, tested at 5, 12, 28, 35, 65, 99, 132 and 193 days after treatment, has no effects on glycaemic and plasmatic total protein levels measured as biomarkers for general stress indexes. Nevertheless, the significant reduction of circulating haemocytes and the basal levels of phenoloxidase (PO) activities recorded in 40-Gy irradiated crayfishes indicate that the exposure shrinks their capability to mount a rapid nonspecific response, and higher levels of plasmatic total PO activity indicate the ability to compensate and maintain an inducible response. Histological analyses performed at the end of the experiment showed no morphological damage in the testicular acini of irradiated males. Moreover, behavioural responses to two different water stimuli (vaporization and jet), measured at 15 and 45 days after the irradiation, were not modified in exposed crayfishes compared to the control group.

CONCLUSIONS

These results confirm the validity of SMRT on young males when the breeding season is less than 4 months but exposure to X-ray should be repeated at mid-breeding season when temperatures allow a longer breeding season. © 2021 Society of Chemical Industry.

Ultrastructural alteration in Gill and Hepatopancrease of freshwater prawn Macrobrachium rosenbergii exposed to 60Co gamma radiation

The present study was designed to evaluate the impact of gamma radiation (⁶⁰Co) on freshwater prawn Macrobrachium rosenbergii by using electron microscopic (SEM, TEM) studies. One set of prawns (experimental group) was irradiated (3, 30, 300, and 3000 mGy) by Theratron Phoenix TeleCobalt Unit [P-33], while other set of prawns (control group) was maintained (non-irradiated) separately. Scanning electron microscopic observations of gills and hepatopancreas showed fused and swollen lamella, abnormal gill tips, wrinkled lamellar epithelium, and necrotic epithelium surface in irradiated groups, while no such abnormalities were obvious in the control group. Transmission electron microscopic studies showed damaged nucleus, granulated mitochondria, vacuoles with crystalline granular inclusions, destructed membrane, vacuoles filled with granules, rough endoplasmic reticulum with residual bodies, shrunken mitochondria, dilated rough endoplasmic reticulum, and dilated cisternae of the Golgi body in irradiated groups. The structural abnormalities of vital organs could affect physiological functions such as respiration, osmo-ionic regulation and storage, secretion of the gills, and hepatopancreas, which in turn could adversely affect the growth and survivability of M. rosenbergii.

Epigenetic, transcriptional and phenotypic responses in Daphnia magna exposed to low-level ionizing radiation

Ionizing radiation is known to induce oxidative stress and DNA damage as well as epigenetic effects in aquatic organisms. Epigenetic changes can be part of the adaptive responses to protect organisms from radiation-induced damage, or act as drivers of toxicity pathways leading to adverse effects. To investigate the potential roles of epigenetic mechanisms in low-dose ionizing radiation-induced stress responses, an ecologically relevant crustacean, adult Daphnia magna were chronically exposed to low and medium level external ⁶⁰Co gamma radiation ranging from 0.4, 1, 4, 10, and 40 mGy/h for seven days. Biological effects at the molecular (global DNA methylation, histone modification, gene expression), cellular (reactive oxygen species formation), tissue/organ (ovary, gut and epidermal histology) and organismal (fecundity) levels were investigated using a suite of effect assessment tools. The results showed an increase in global DNA methylation associated with loci-specific alterations of histone H3K9 methylation and acetylation, and downregulation of genes involved in DNA methylation, one-carbon metabolism, antioxidant defense, DNA repair, apoptosis, calcium signaling and endocrine regulation of development and reproduction. Temporal changes of reactive oxygen species (ROS) formation were also observed with an apparent transition from ROS suppression to induction from 2 to 7 days after gamma exposure. The cumulative fecundity, however, was not significantly changed by the gamma exposure. On the basis of the new experimental evidence and existing knowledge, a hypothetical model was proposed to provide in-depth mechanistic understanding of the roles of epigenetic mechanisms in low dose ionizing radiation induced stress responses in D. magna.

Chernobyl-level radiation exposure damages bumblebee reproduction: a laboratory experiment

The consequences for wildlife of living in radiologically contaminated environments are uncertain. Previous laboratory studies suggest insects are relatively radiation-resistant; however, some field studies from the Chernobyl Exclusion Zone report severe adverse effects at substantially lower radiation dose rates than expected. Here, we present the first laboratory investigation to study how environmentally relevant radiation exposure affects bumblebee life history, assessing the shape of the relationship between radiation exposure and fitness loss. Dose rates comparable to the Chernobyl Exclusion Zone (50-400 µGy h-1) impaired bumblebee reproduction and delayed colony growth but did not affect colony weight or longevity. Our best-fitting model for the effect of radiation dose rate on colony queen production had a strongly nonlinear concave relationship: exposure to only 100 µGy h-1 impaired reproduction by 30-45%, while further dose rate increases caused more modest additional reproductive impairment. Our data indicate that the practice of estimating effects of environmentally relevant low-dose rate exposure by extrapolating from high-dose rates may have considerably underestimated the effects of radiation. If our data can be generalized, they suggest insects suffer significant negative consequences at dose rates previously thought safe; we therefore advocate relevant revisions to the international framework for radiological protection of the environment.

Radiation-induced transgenerational effects in animals

According to the results of recent studies, parental exposure to ionizing radiation not only leads to mutation induction in the germline of irradiated animals but also affects their non-exposed offspring. These radiation-induced transgenerational effects belong to an epigenetic phenomenon that could not be defined as a transmission of altered phenotypes from the irradiated parents to their non-exposed offspring. In this review, we present the results of laboratory studies aimed to evaluate the transgenerational effects of parental irradiation on a number of traits in the offspring of exposed parents. The results of animal studies showing compromised viability, fertility and genome stability among the non-exposed offspring of irradiated parents are presented and discussed. So far, the epigenetic phenomenon of radiation-induced transgenerational effects has been established in laboratory studies. Future work should address the important issue of manifestation of radiation-induced transgenerational effects in populations inhabiting radioactive-contaminated areas, as well as the mechanisms of transgenerational effects.

Is developmental instability in chironomids a sensitive endpoint for testing uranium mine-affected sediments?

There is increasing interest in effects of radionuclides on non-human species, but methods for studying such effects are not well developed. The aims of the current study were to investigate the effects of uranium mine-affected sediments on non-biting midge Chironomus riparius and to compare sensitivity of different endpoints. The midge larvae were exposed in controlled laboratory conditions to sediments from two ponds downstream from an abandoned uranium mine and a reference pond not receiving water from the mining site. Quartz sand was used as an additional control. Developmental effects were assessed by evaluating emergence of adult midges, body mass, and fluctuating asymmetry (FA) in the length of wing upper vein. FA has been suggested to be a sensitive indicator of developmental instability, but the results of previous studies are inconsistent. In the present study, no difference in FA was observed between the treatment groups, but time to emergence was significantly delayed in the contaminated sediments. The approach used in this study (laboratory experiments with sediments from a contaminated site) avoids confounding due to uncontrolled environmental variables and adaptation to long-term contamination, which may mask effects on natural populations. Using this approach, we found no effects on FA of wing length. Time to emergence, in contrast, was found to be a more sensitive endpoint.

Integrative assessment of low-dose gamma radiation effects on Daphnia magna reproduction: Toxicity pathway assembly and AOP development

High energy gamma radiation is potentially hazardous to organisms, including aquatic invertebrates. Although extensively studied in a number of invertebrate species, knowledge on effects induced by gamma radiation is to a large extent limited to the induction of oxidative stress and DNA damage at the molecular/cellular level, or survival, growth and reproduction at the organismal level. As the knowledge of causal relationships between effects occurring at different levels of biological organization is scarce, the ability to provide mechanistic explanation for observed adverse effects is limited, and thus development of Adverse Outcome Pathways (AOPs) and larger scale implementation into next generation hazard and risk predictions is restricted. The present study was therefore conducted to assess the effects of high-energy gamma radiation from cobalt-60 across multiple levels of biological organization (i.e., molecular, cellular, tissue, organ and individual) and characterize the major toxicity pathways leading to impaired reproduction in the model freshwater crustacean Daphnia magna (water flea). Following gamma exposure, a number of bioassays were integrated to measure relevant toxicological endpoints such as gene expression, reactive oxygen species (ROS), lipid peroxidation (LPO), neutral lipid storage, adenosine triphosphate (ATP) content, apoptosis, ovary histology and reproduction. A non-monotonic pattern was consistently observed across the levels of biological organization, albeit with some variation at the lower end of the dose-rate scale, indicating a complex response to radiation doses. By integrating results from different bioassays, a novel pathway network describing the key toxicity pathways involved in the reproductive effects of gamma radiation were proposed, such as DNA damage-oocyte apoptosis pathway, LPO-ATP depletion pathway, calcium influx-endocrine disruption pathway and DNA hypermethylation pathway. Three novel AOPs were proposed for oxidative stressor-mediated excessive ROS formation leading to reproductive effect, and thus introducing the world's first AOPs for non-chemical stressors in aquatic invertebrates.

Does Salinity Affect the Distribution of the Artificial Radionuclides 90Sr and 137Cs in Water of the Saline Lakes? A Case of the Crimean Peninsula

In the framework of radioecological monitoring, the features of the distribution of the post-Chernobyl nuclear power plant (NPP) accident artificial radionuclides of 137Cs and 90Sr in the Crimean saline lakes were studied. Samples were collected from 12 Crimean lakes with a salinity range from 2 to 400 g/L in 2014–2017. Concentration of 90Sr varied from 5.9 to 313.6 Bq/m3, and 137Cs from 0.8 to 106.7 Bq/m3. Closing of the North Crimean Canal resulted in a decrease in radionuclide concentration in the lakes. About 61% of the total variability of 90Sr and 33% of 137Cs in lake water can be explained by salinity changes. The salinity affects the behavior of radionuclides in water, mainly influencing their solubility, on isotope exchange between the solution and bottom sediments, and also, probably, through its influence on accumulation of isotopes by aquatic organisms. Salinity is not the alone factor determining the behavior of radionuclides in the lakes, it only acts by interacting with other factors.

Impacts of ionising radiation on sperm quality, DNA integrity and post-fertilisation development in marine and freshwater crustaceans

Crustaceans have been designated as internationally important model organisms in the development of environmental radioprotection measures. Despite the known sensitivity of sperm to ionizing radiation, the impacts of chronic radiation exposure on male fertility in crustaceans have not been studied. For the first time, the present study aimed to assess the impacts of chronic radiation exposure on male fertility, sperm DNA damage and concomitant impacts on breeding in two amphipod crustaceans. Echinogammarus marinus and Gammarus pulex (male fertility only) were exposed to phosphorus-32 at dose rates of 0, 0.1, 1 and 10 mGy/d and sperm parameters, DNA damage and knock-on impacts on breeding were assessed. Sperm quality parameters and DNA damage were assessed using a fluorescent staining method and single cell gel electrophoresis respectively. Concomitant effects of male exposure to radiation on fecundity were determined by pairing phosphorus-32 exposed males to unexposed sexually mature females. In E. marinus, a statistically significant reduction of 9 and 11% in the quality of sperm was recorded at dose rates of 1 and 10 mGy/d respectively, with no significant effects recorded on sperm counts. Conversely in the freshwater G. pulex, no significant impact of radiation on sperm quantity or quality was recorded. For E. marinus, a statistically significant increase in DNA damage was recorded at doses of 10 mGy/d. Reduced fecundity and an increase in the frequency of abnormal embryos was recorded in female E. marinus breeding with males exposed to radiation. These findings suggest sperm quality may be a sensitive indicator of radiation exposure in invertebrates with potential impacts on the unexposed embryo, though unclear dose-response and differences between two closely related species necessitate further study before robust conclusions can be drawn.

Chronic radiation exposure at Chernobyl shows no effect on genetic diversity in the freshwater crustacean, Asellus aquaticus thirty years on

Analysis of genetic diversity represents a fundamental component of ecological risk assessments in contaminated environments. Many studies have assessed the genetic implications of chronic radiation exposure at Chernobyl, generally recording an elevated genetic diversity and mutation rate in rodents, plants, and birds inhabiting contaminated areas. Only limited studies have considered genetic diversity in aquatic biota at Chernobyl, despite the large number of freshwater systems where elevated dose rates will persist for many years. Consequently, the present study aimed to assess the effects of chronic radiation exposure on genetic diversity in the freshwater crustacean, Asellus aquaticus, using a genome-wide SNP approach (Genotyping-by-sequencing). It was hypothesized that genetic diversity in A. aquaticus would be positively correlated with dose rate. A. aquaticus was collected from six lakes in Belarus and the Ukraine ranging in dose rate from 0.064 to 27.1 µGy/hr. Genotyping-by-sequencing analysis was performed on 74 individuals. A significant relationship between geographical distance and genetic differentiation confirmed the Isolation-by-Distance model. Conversely, no significant relationship between dose rate and genetic differentiation suggested no effect of the contamination gradient on genetic differentiation between populations. No significant relationship between five measures of genetic diversity and dose rate was recorded, suggesting that radiation exposure has not significantly influenced genetic diversity in A. aquaticus at Chernobyl. This is the first study to adopt a genome-wide SNP approach to assess the impacts of environmental radiation exposure on biota. These findings are fundamental to understanding the long-term success of aquatic populations in contaminated environments at Chernobyl and Fukushima.

Identification of Cofilin-1 and Destrin as Potential Early-warning Biomarkers for Gamma Radiation in Mouse Liver Tissues

Gamma radiation causes cell injury and leads to an increased risk of cancer, so it is of practical significance to identify biomarkers for gamma radiation. We used proteomic analysis to identify differentially expressed proteins in liver tissues of C57BL/6J mice treated with gamma radiation from Cs for 360 d. We confirmed obvious pathological changes in mouse liver tissues after irradiation. Compared with the control group, 74 proteins showed a fold change of ≥1.5 in the irradiated groups. We selected 24 proteins for bioinformatics analysis and peptide mass fingerprinting and found that 20 of the identified proteins were meaningful. These proteins were associated with tumorigenesis, tumor suppression, catalysis, cell apoptosis, cytoskeleton, metabolism, gene transcription, T-cell response, and other pathways. We confirmed that both cofilin-1 and destrin were up regulated in the irradiated groups by western blot and real-time polymerase chain reaction. Our findings indicate that cofilin-1 and destrin are sensitive to gamma radiation and may be potential biomarkers for gamma radiation. Whether these proteins are involved in radiation-induced tumorigenesis requires further investigation.

The combined effects of acute irradiation and food supply on survival and fertility in Daphnia magna

The results of recent studies have provided strong evidence for the combined effects of diet restriction and exposure to chemical on the survival and reproduction of aquatic organisms. However, the combined effects of diet restriction and exposure to ionizing radiation remain poorly understood. To establish whether parental irradiation and diet restriction can affect the survival and fertility of directly exposed crustaceans and their progeny, Daphnia magna were given 10, 100 and 1000 mGy of acute γ-rays either during chronic diet restriction or normal food supply. Acute exposure to 1000 mGy significantly compromised the viability of irradiated Daphnia and their first-generation progeny, but did not affect the second-generation progeny. Similarly acute exposure to 100 and 1000 mGy also significantly compromised the fertility of F₀ and F₁Daphnia and did not affect the F₂ generation. Low level of food supply compromised the viability of non-exposed and irradiated Daphnia, whereas their fertility was substantially affected by all diets. The dose-response for the effects of irradiation on viability and fertility of Daphnia received different food supply were practically similar, thus implying that the level of nutrition and acute exposure to ionizing radiation independently affect the life history traits in crustacean.

Life history traits and genotoxic effects on Daphnia magna exposed to waterborne uranium and to a uranium mine effluent - A transgenerational study

Assessing the impact of uranium mining industry on aquatic ecosystems near mining areas is critical to ensure the long-term health and sustainability of ecosystem services. As so, a transgenerational study with Daphnia magna has been conducted to perceive to what extent intermittent discharges of uranium mine effluents into watercourses may impact the DNA integrity and life history traits of cladocerans. Organisms were exposed for 48 h to a 2% dilution of an uranium mine effluent (UME) and to a corresponding dose of waterborne uranium (WU) that, according to our preliminary studies, induces significant DNA damage in daphnids. After exposure, organisms were transferred to clean medium, where three successive generations were monitored for genotoxicity and other effects at the individual and population level. Despite some differences between WU and UME data, our results revealed that the negative impacts of the short-term exposure gradually disappeared after placing the organisms in clean medium. These results suggest that, under intermittent stress, daphnids are able to recover, since after the 3^rd brood release, DNA damage (measured as DNA strand breaks) is no longer observed and has no significant impact on the detectable life traits of offspring. Although our results indicate that populations of D. magna are not affected by intermittent and highly diluted discharges from uranium mining, aquatic systems under this kind of pressure should not be seen as hazardous-free. Future studies in this field are recommended and these should consider radionuclides in the water column, their accumulation in the sediments and also multiple life stages.

Reproduction in the freshwater crustacean Asellus aquaticus along a gradient of radionuclide contamination at Chernobyl

Nuclear accidents such as Chernobyl and Fukushima have led to contamination of the environment that will persist for many years. The consequences of chronic low-dose radiation exposure for non-human organisms inhabiting contaminated environments remain unclear. In radioecology, crustaceans are important model organisms for the development of environmental radioprotection. Previous laboratory studies have demonstrated deleterious effects of radiation exposure on crustacean reproduction. However, no studies have documented the effects of chronic radiation exposure on the reproduction of natural crustacean populations. Based on data from laboratory exposures, we hypothesised that populations of the freshwater isopod Asellus aquaticus exposed to radiation for thirty years at Chernobyl would display reduced reproductive output and altered timing of reproduction. To test this hypothesis, A. aquaticus was collected from six lakes at Chernobyl over two years with total dose rates ranging from 0.06-27.1μGy/h. No significant differences in the fecundity, mass of broods or proportion of reproducing female A. aquaticus were recorded. Significant differences in the body mass of gravid females were recorded suggesting different timings of reproduction, however this was not related to radiation contamination. No significant effect of a range of environmental parameters on A. aquaticus reproduction was recorded. Our data suggests current dose rates at Chernobyl are not causing discernible effects on the reproductive output of A. aquaticus. This study is the first to assess the effects of chronic low-dose radiation exposure on the reproductive output of an aquatic invertebrate at Chernobyl. These findings are consistent with proposed radiological protection benchmarks for the maintenance of wildlife populations and will assist in management of environments impacted by radiation.

Gamma radiation induces dose-dependent oxidative stress and transcriptional alterations in the freshwater crustacean Daphnia magna

Among aquatic organisms, invertebrate species such as the freshwater crustacean Daphnia magna are believed to be sensitive to gamma radiation, although information on responses at the individual, biochemical and molecular level is scarce. Following gamma radiation exposure, biological effects are attributed to the formation of free radicals, formation of reactive oxygen species (ROS) and subsequently oxidative damage to lipids, proteins and DNA in exposed organisms. Thus, in the present study, effects and modes of action (MoA) have been investigated in D. magna exposed to gamma radiation (dose rates: 0.41, 1.1, 4.3, 10.7, 42.9 and 106 mGy/h) after short-term exposure (24 and 48 h). Several individual, cellular and molecular endpoints were addressed, such as ROS formation, lipid peroxidation, DNA damage and global transcriptional changes. The results showed that oxidative stress is one of the main toxic effects in gamma radiation exposed D. magna, mediated by the dose-dependent increase in ROS formation and consequently oxidative damage to lipids and DNA over time. Global transcriptional analysis verified oxidative stress as one of the main MoA of gamma radiation at high dose rates, and identified a number of additional MoAs that may be of toxicological relevance. The present study confirmed that acute exposure to gamma radiation caused a range of cellular and molecular effects in D. magna exposed to intermediate dose rates, and highlights the need for assessing effects at longer and more environmentally relevant exposure durations in future studies.

RIBE at an inter-organismic level: A study on genotoxic effects in Daphnia magna exposed to waterborne uranium and a uranium mine effluent

The induction of RIBE (Radiation Induced Bystander Effect) is a non-target effect of low radiation doses that has already been verified at an inter-organismic level in fish and small mammals. Although the theoretical impact in the field of environmental risk assessment (ERA) is possible, there is a gap of knowledge regarding this phenomenon in invertebrate groups and following environmentally relevant exposures. To understand if RIBE should be considered for ERA of radionuclide-rich wastewaters, we exposed Daphnia magna (<24 h and 5d old) to a 2% diluted uranium mine effluent for 48 h, and to a matching dose of waterborne uranium (55.3 μg L^-1). Then the exposed organisms were placed (24 and 48 h) in a clean medium together with non-exposed neonates. The DNA damage observed for the non-exposed organisms was statistically significant after the 24 h cohabitation for both uranium (neonates p = 0.002; 5 d-old daphnids p = <0.001) and uranium mine effluent exposure (only for neonates p = 0.042). After 48 h cohabitation significant results were obtained only for uranium exposure (neonates p = 0.017; 5 d-old daphnids p = 0.013). Although there may be some variability associated to age and exposure duration, the significant DNA damage detected in non-exposed organisms clearly reveals the occurrence of RIBE in D. magna. The data obtained and here presented are a valuable contribution for the discussion about the relevance of RIBE for environmental risk assessment.

Up-regulation of calreticulin in mouse liver tissues after long-term irradiation with low-dose-rate gamma rays

The biological effects of low-dose or low-dose-rate ionizing radiation on normal tissues has attracted attention. Based on previous research, we observed the morphology of liver tissues of C57BL/6J mice that received <50, 50–500, and 500–1000 μGy/h of ¹³⁷Cs radiation for 180 d. We found that the pathological changes in liver tissues were more obvious as the irradiation dose rates increased. Additionally, differential protein expression in liver tissues was analyzed using a proteomics approach. Compared with the matched group in the 2D gel analysis of the irradiated groups, 69 proteins had ≥ 1.5-fold changes in expression. Twenty-three proteins were selected based on ≥2.5-fold change in expression, and 22 of them were meaningful for bioinformatics and protein fingerprinting analysis. These molecules were relevant to cytoskeleton processes, cell metabolism, biological defense, mitochondrial damage, detoxification and tumorigenesis. The results from real-time PCR and western blot (WB) analyses showed that calreticulin (CRT) was up-regulated in the irradiated groups, which indicates that CRT may be relevant to stress reactions when mouse livers are exposed to low-dose irradiation and that low-dose-rate ionizing radiation may pose a cancer risk. The CRT protein can be a potential candidate for low-dose or low-dose-rate ionizing radiation early-warning biomarkers. However, the underlying mechanism requires further investigation.

Calorimetrically Determined U(VI) Toxicity in Brassica napus Correlates with Oxidoreductase Activity and U(VI) Speciation

Radioecological studies depend on the quantitative toxicity assessment of environmental radionuclides. At low dose exposure, the life span of affected organisms is barely shortened, enabling the transfer of radionuclides through an almost-intact food chain. Lethality-based toxicity estimates are not adequate in this regime because they require higher concentrations. However, increased radionuclide concentration alters its speciation, rendering the extrapolation to the low dose exposure chemically inconsistent. Here, we demonstrate that microcalorimetry provides a sensitive real-time monitor of toxicity of uranium (in the U(VI) oxidation state) in a plant cell model of Brassica napus. We introduce the calorimetric descriptor "metabolic capacity" and show that it correlates with enzymatically determined cell viability. It is independent of physiological models and robust against the naturally occurring fluctuations in the metabolic response to U(VI) of plant cell cultures. In combination with time-resolved laser-induced fluorescence spectroscopy and thermodynamic modeling, we show that the plant cell metabolism is affected predominantly by hydroxo-species of U(VI) with an IC₅₀ threshold of ∼90 μM. The data emphasize the yet-little-exploited potential of microcalorimetry for the speciation-sensitive ecotoxicology of radionuclides.

Interpopulational variability of molecular responses to ionizing radiation in freshwater bivalves Anodonta anatina (Unionidae)

Freshwater ecosystems are exposed to multiple anthropogenic stressors including chemical pollution and warming that can affect health of the resident organisms and their responses to novel challenges. We investigated the of in situ exposure history on molecular responses to a novel stressor, ionizing radiation, in unionid mollusks Anodonta anatina. Males from pristine (F-), agricultural (A-) sites and a cooling reservoir of a nuclear power plant (N-site) were exposed to acute low dose (2mGy) X-ray radiation followed by 14days of recovery (R-groups) or to control conditions (C-groups). Biomarkers of oxidative stress, geno-, cyto- and neurotoxicity were used to assess cellular injury and stress. Control group from the cooling reservoir (CN) had higher background levels of caspase-3 activity, metallothionein concentrations and nuclear lesions and lower levels of superoxide dismutase (SOD) and glutathione in the gills compared to other control groups (CF and CA). Irradiation induced cellular damage in mussels from all three sites including increased levels of nuclear lesions in hemocytes, depletion of caspase-3, suppression of superoxide dismutase and catalase activities, an increase of the lipid peroxidation and oxidized glutathione levels, as well as down-regulation of cholinesterase indicating neurotoxicity. The up-regulation of ethoxyresorufin-O-deethylase activity in the digestive gland and vitellogenin-like protein level in gonads were also found in radiation-exposed groups indicating feminization of males and disturbances of xenobiotic metabolism. The RA-group showed the greatest magnitude of radiation-induced stress responses compared to the other two groups. Overall, unionid mollusks, particularly those from a chronically polluted agricultural site, were highly sensitive to low-dose radiation (2mGy) indicating limitations of stress protection mechanisms to deal with multiple stressors.

The long-term effects of acute exposure to ionising radiation on survival and fertility in Daphnia magna

The results of recent studies have provided strong evidence for the transgenerational effects of parental exposure to ionising radiation and chemical mutagens. However, the transgenerational effects of parental exposure on survival and fertility remain poorly understood. To establish whether parental irradiation can affect the survival and fertility of directly exposed organisms and their offspring, crustacean Daphnia magna were given 10, 100, 1000 and 10,000mGy of acute γ-rays. Exposure to 1000 and 10,000mGy significantly compromised the viability of irradiated Daphnia and their first-generation progeny, but did not affect the second-generation progeny. The fertility of F0 and F1Daphnia gradually declined with the dose of parental exposure and significantly decreased at dose of 100mGy and at higher doses. The effects of parental irradiation on the number of broods were only observed among the F0Daphnia exposed to 1000 and 10,000mGy, whereas the brood size was equally affected in the two consecutive generations. In contrast, the F2 total fertility was compromised only among progeny of parents that received the highest dose of 10,000mGy. We propose that the decreased fertility observed among the F2 progeny of parents exposed to 10,000mGy is attributed to transgenerational effects of parental irradiation. Our results also indicate a substantial recovery of the F2 progeny of irradiated F0Daphnia exposed to the lower doses of acute γ-rays.