A multi-criteria weight of evidence approach for deriving ecological benchmarks for radioactive substances

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.

Changes in the structural and functional state of the thyroid gland of small mammals when exposed to low-intensity chronic radiation

The study gives a morphofunctional assessment of the state of the thyroid gland of tundra voles (Microtus oeconomus Pall.) in conditions of an increased radiation background (the Ukhta district of the Komi Republic (Russia) and the 30-km zone of the Chernobyl NPP), as well as in an experiment with chronic external gamma irradiation in the low dose range. The work summarizes the experience of more than 35 years of field and laboratory research. The authors have noted the high sensitivity of the thyroid gland to chronic radiation against the general irradiation of the organism both in natural conditions and in the experiment. The repeatability of the observed effects in voles from natural populations and the comparability of some effects with the morphological changes occurring in animals after exposure to ionizing radiation in the experiment indicates the radiation nature of these effects. The tundra voles living in conditions of increased radiation background have been identified for a greater variety of morphological rearrangements in the thyroid parenchyma than the experimental animals. The complex and ambiguous nature of the thyroid gland responses to radiation exposure indicates the possibility of a significant increase in the risk of negative effects of ionizing radiation in contrast with the expected results of biological effects' extrapolation from high to low doses.

Ionizing radiation exposure effects across multiple generations: evidence and lessons from non-human biota

A Task Group (TG121) of the International Commission on Radiological Protection (ICRP) Committee 1 was launched in 2021 to study the effects of ionizing radiation in offspring and next generations. In this report, we summarize the evidence of multi- and trans-generational effects in non-human biota species that was discussed at the ICRP workshop entitled "Effects of Ionizing Radiation Exposure in Offspring and Next Generations" in June 2022. Epigenetic changes, including changes in DNA methylation, have been observed in trans- and multi-generational irradiation studies in both plants and animals. There were also reports of changes in offspring survival and reproduction. The reported evidence for altered reproduction is an area of potential concern, due to possible effects at the population or ecosystem level. Different considerations are also discussed regarding non-human biota data, such as transferability of data between different species or extending knowledge to humans, differences in species radiosensitivity, the presence of adaptive responses, and dose reconstruction for exposures that occur across multiple generations. Overall, there is a diverse range of available data of the effects in non-human biota, and it will require careful consideration when incorporating this evidence into the system of radiological protection of humans and of the environment.

Bioaccumulation and risk assessment of radiocesium in the Northwest Pacific Ocean from Fukushima Dai-ichi Nuclear Power Plant accident

To understand which biota are more exposed to radionuclides, the bioaccumulation and risk assessment of radiocesium (137Cs and 134Cs) release from FDNPP in the Northwest Pacific Ocean were analyzed using ERICA tools. The activity level was determined by the Japanese Nuclear Regulatory Authority (RNA) in 2013. The data were used as input to the ERICA Tool modeling software to evaluate the accumulation and dose of marine organisms. The highest and lowest accumulate concentration rate were observed in birds (4.78E+02 Bq kg-1/Bq L-1) and the Vascular plant (1.04E+01 Bq kg-1/Bq L-1), respectively. The total dose rate range for the 137Cs and 134Cs ranged between 7.39E-04 and 2.65E+00 μGy h-1 and 4.24E-05 and 2.91E-01 μGy h-1, respectively. There is no considerable risk to the marine biota in the research region since the cumulative dose rates of radiocesium to the chosen species were all less than 10 μGy h-1.

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.

Insights into the modes of action of tritium on the early-life stages of zebrafish, Danio rerio, using transcriptomic and proteomic analyses

In the environment, populations are exposed to different kinds of ionizing radiation. Little is known about their modes of action on non-human species, and whether or not they are similar for alpha, beta and gamma radiations, considered as the reference. In this context, tritium effects (beta emitter) under the form of tritiated water (HTO) were investigated in zebrafish, a common model in toxicology and ecotoxicology with a fully sequenced genome. Experiments were conducted on early life stages, considered to be highly sensitive to pollutants, by exposing eggs to 0.4 mGy/h of HTO until 10 days post fertilization. Tritium internalization was quantified, and effects were investigated using a combined approach of transcriptomic and proteomic analyses. Results highlighted similarities in the biological pathways affected by HTO by both techniques, such as defence response, muscle integrity and contraction, and potential visual alterations. These results correlated well with previous data obtained on earlier developmental stages (1 and 4 dpf). Interestingly, HTO effects were partly overlapping those obtained after gamma irradiation, underlying potential common modes of action. This study, therefore, brought a body of evidence on the effects of HTO observed at the molecular level on zebrafish larvae. Further studies could investigate if the effects persist in adult organisms.

Threshold values for the protection of marine ecosystems from NORM in subsea oil and gas infrastructure

This modelling study uses the ERICA Tool and Bateman's equation to derive sediment threshold values for radiation protection of the marine environment relevant to NORM-contaminated products (radium-contaminated scales, ²¹⁰Pb films and ²¹⁰Po films) found in subsea oil and gas infrastructure. Threshold values are calculated as the activity concentration of the NORM-contaminated products' head of chain radionuclide (i.e., ²²⁶Ra + ²²⁸Ra, ²¹⁰Pb, or ²¹⁰Po) that will increase radiation dose rates in sediments by 10 μGy/h to the most exposed organism at a given release time. The minimum threshold value (corresponding to peak radiation dose rates from the ingrowth of progeny) were for radium-contaminated scales, 0.009 Bq/g of ²²⁶Ra, 0.029 Bq/g of ²²⁸Ra (in the absence of ²²⁶Ra) or 0.14 Bq/g of ²²⁸Ra (in the presence of ²²⁶Ra), followed by 0.015 Bq/g for ²¹⁰Pb films, and 1.6 Bq/g for ²¹⁰Po films. These may be used as default threshold values. Added activity concentrations of the NORM-contaminated products to marine sediments below these threshold values implies a low radiological risk to organisms while exceedances imply that further investigation is necessary. Using contaminated product specific parameterisations, such as K_d values derived for Ra from a BaSO₄ matrix in seawater, could greatly affect threshold values. Strong consideration should be given to deriving such data as part of specific radiological risk assessments for these products.

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.

Best practices for predictions of radionuclide activity concentrations and total absorbed dose rates to freshwater organisms exposed to uranium mining/milling

Predictions of radionuclide dose rates to freshwater organisms can be used to evaluate the radiological environmental impacts of releases from uranium mining and milling projects. These predictions help inform decisions on the implementation of mitigation measures. The objective of this study was to identify how dose rate modelling could be improved to reduce uncertainty in predictions to non-human biota. For this purpose, we modelled the activity concentrations of ²¹⁰Pb, ²¹⁰Po, ²²⁶Ra, ²³⁰Th, and ²³⁸U downstream of uranium mines and mills in northern Saskatchewan, Canada, together with associated weighted absorbed dose rates for a freshwater food chain using measured activity concentrations in water and sediments. Differences in predictions of radionuclide activity concentrations occurred mainly from the different default partition coefficient and concentration ratio values from one model to another and including all or only some ²³⁸U decay daughters in the dose rate assessments. Consequently, we recommend a standardized best-practice approach to calculate weighted absorbed dose rates to freshwater biota whether a facility is at the planning, operating or decommissioned stage. At the initial planning stage, the best-practice approach recommend using conservative site-specific baseline activity concentrations in water, sediments and organisms and predict conservative incremental activity concentrations in these media by selecting concentration ratios based on species similarity and similar water quality conditions to reduce the uncertainty in dose rate calculations. At the operating and decommissioned stages, the best-practice approach recommends relying on measured activity concentrations in water, sediment, fish tissue and whole-body of small organisms to further reduce uncertainty in dose rate estimates. This approach would allow for more realistic but still conservative dose assessments when evaluating impacts from uranium mining projects and making decision on adequate controls of releases.

Multigenerational exposure to gamma radiation affects offspring differently over generations in zebrafish

Mutigenerational studies are now of great interest in ecotoxicology and previous studies have shown the importance of conducting multigenerational studies when assessing radiation toxicity in fish. In our study, the first objective was to study the early life stages (embryo-larval stages) and critical functions such as reproduction (which are generally studied in the context of ecological risk assessment (ERA)), in order to assess the sensitivity of zebrafish to ionizing radiation. The second objective was to assess acquisition of phenotypic effects at select life stages over generations. To our knowledge, this was the first time that irradiation of zebrafish (0.05 and 5 mGy.h^-1) up to generation F2 was maintained with the following two exposure conditions: (1) recovery, only F0 genitors were irradiated and the progeny were placed in control condition, (2) irradiated condition, all generations were exposed. Multigenerational irradiation affected F1 parental reproductive capacity (reproductive success) mainly over the first reproductive cycle (104d) and larval survival rate. Unexpected yet significant effects on sex ratio were observed in F1 progeny after parental irradiation (mainly at 5 mGy.h^-1). These effects were observed for both conditions -irradiated and recovery- suggesting transmitted effects from F0 genitors to offspring. All studied life stages were affected by ionizing radiation (IR), suggesting an alteration of vital physiological functions (reproduction and sexual determination). Such results highlight the hypothesis that IR affects population dynamics. In addition, the clear evidence of transmitted effects suggests worsening of effects at the population scale over generations. This approach is closer to environmental conditions to assess wild population fate, and thus highlights the importance of multigenerational studies to support ERA of ionizing radiation in fish.

Changes in Growth, Morphology, and Physiology of Tetrahymena pyriformis Exposed to Continuous Cesium-137 and Cobalt-60 Gamma-Radiation

This study investigated the effects of gamma-radiation on Tetrahymena pyriformis. The experimental approach consists of exposing T. pyriformis growing in presence of Cesium-137 (¹³⁷Cs) at dose rates of 1, 2, 4, and 6 cGy h^-1 and Cobalt-60 (⁶⁰Co) at dose rates of 8, 10, 15, and 20 cGy h^-1. The radiation doses effects on growth, morphology, some metabolic enzymes, and reactive oxygen species (ROS) markers have been evaluated. When cells were growing in irradiating conditions at dose rates beyond 4 cGy h^-1, a decreasing of cells and generation numbers with a prolongation of generation time and a change of morphological aspect with rounding-off of cells were observed compared to the control. The 50%-inhibitory dose (ID₅₀) for radiation was estimated at 1568.72 ± 158.45 cGy. The gamma-radiation at dose rates more than 6 cGy h^-1, affected both glyceraldehyde 3-phosphate dehydrogenase and succinate dehydrogenase by inhibiting their activities. All of these effects were more pronounced when cells were irradiated at the dose rate of 20 cGy h^-1 using ⁶⁰Co source. For ROS markers generated by gamma-radiation in T. pyriformis, the results showed an increase of the lipid peroxidation in cells grown in presence of gamma-radiation at dose rates more than 6 cGy h^-1 and an enhancement in catalase and superoxide dismutase activities from the dose rate of 1 cGy h^-1. These encouraging results suggested the use of T. pyriformis as a unicellular model cell to investigate other aspects of the response to ionizing radiation.

Current understanding and research needs for ecological risk assessments of naturally occurring radioactive materials (NORM) in subsea oil and gas pipelines

Thousands of offshore oil and gas facilities are coming to the end of their life in jurisdictions worldwide and will require decommissioning. In-situ decommissioning, where the subsea components of that infrastructure are left in the marine environment following the end of its productive life, has been proposed as an option that delivers net benefits, including from: ecological benefits from the establishment of artificial reefs, economic benefits from associated fisheries, reduced costs and improved human safety outcomes for operators. However, potential negative impacts, such as the ecological risk of residual contaminants, are not well understood. Naturally occurring radioactive materials (NORM) are a class of contaminants found in some oil and gas infrastructure (e.g. pipelines) and includes radionuclides of uranium, thorium, radium, radon, lead, and polonium. NORM are ubiquitous in oil and gas reservoirs around the world and may form contamination products including scales and sludges in subsea infrastructure due to their chemistries and the physical processes of oil and gas extraction. The risk that NORM from these sources pose to marine ecosystems is not yet understood meaning that decisions made about decommissioning may not deliver the best outcomes for environments. In this review, we consider the life of NORM-contamination products in oil and gas systems, their expected exposure pathways in the marine environment, and possible ecological impacts following release. These are accompanied by the key research priorities that need to better describe risk associated with decommissioning options.

An updated strategic research agenda for the integration of radioecology in the european radiation protection research

The ALLIANCE Strategic Research Agenda (SRA) for radioecology is a living document that defines a long-term vision (20 years) of the needs for, and implementation of, research in radioecology in Europe. The initial SRA, published in 2012, included consultation with a wide range of stakeholders (Hinton et al., 2013). This revised version is an update of the research strategy for identified research challenges, and includes a strategy to maintain and develop the associated required capacities for workforce (education and training) and research infrastructures and capabilities. Beyond radioecology, this SRA update constitutes a contribution to the implementation of a Joint Roadmap for radiation protection research in Europe (CONCERT, 2019a). This roadmap, established under the H2020 European Joint Programme CONCERT, provides a common and shared vision for radiation protection research, priority areas and strategic objectives for collaboration within a European radiation protection research programme to 2030 and beyond. Considering the advances made since the first SRA, this updated version presents research challenges and priorities including identified scientific issues that, when successfully resolved, have the potential to impact substantially and strengthen the system and/or practice of the overall radiation protection (game changers) in radioecology with regard to their integration into the global vision of European research in radiation protection. An additional aim of this paper is to encourage contribution from research communities, end users, decision makers and other stakeholders in the evaluation, further advancement and accomplishment of the identified priorities.

A few considerations on some current modelling approaches to assess the impact of radiation on the population size of wildlife species

This note outlines some features of current state-of-the-art models aimed at assessing the radiological impact on wildlife. Such models can be interpreted as particular realisations of an archetypal model from which they can be derived on the basis of specific hypotheses described and analysed here. A stressor can influence, to varying degrees, on the one hand, the inherent biological mortality of a species and, on the other hand, the actual mortality of a species competing for survival in the ecosystem. Generally, the actual mortality rate of a species impacted by a stressor is linked through complicated mathematical relationships to the excess biological mortality caused by the stressor. Such relationships may depend on the particular type of model. The models can be of help to select criteria for the assessment of the radiological impact and to identify suitable parameters for its evaluation.

Deciphering Differential Life Stage Radioinduced Reproductive Decline in Caenorhabditis elegans through Lipid Analysis

Wildlife is chronically exposed to various sources of ionizing radiations, both environmental or anthropic, due to nuclear energy use, which can induce several defects in organisms. In invertebrates, reproduction, which directly impacts population dynamics, has been found to be the most radiosensitive endpoint. Understanding the underlying molecular pathways inducing this reproduction decrease can help in predicting the effects at larger scales (i.e., population). In this study, we used a life stage dependent approach in order to better understand the molecular determinants of reproduction decrease in the roundworm C. elegans. Worms were chronically exposed to 50 mGy·h⁻¹ external gamma ionizing radiations throughout different developmental periods (namely embryogenesis, gametogenesis, and full development). Then, in addition to reproduction parameters, we performed a wide analysis of lipids (different class and fatty acid via FAMES), which are both important signaling molecules for reproduction and molecular targets of oxidative stress. Our results showed that reproductive defects are life stage dependent, that lipids are differently misregulated according to the considered exposure (e.g., upon embryogenesis and full development) and do not fully explain radiation induced reproductive defects. Finally, our results enable us to propose a conceptual model of lipid signaling after radiation stress in which both the soma and the germline participate.

Effects of gamma ionizing radiation exposure on Danio rerio embryo-larval stages - comparison with tritium exposure

The objective was to investigate the effects of ionizing radiation induced in zebrafish early life stages by coupling responses obtained at the molecular (genotoxicity, ROS production, gene expression) and phenotypic (tissue alteration, embryo-larval development) levels. Here we present results obtained after exposure of 3 hpf larvae to 10 days of gamma irradiation at 3.3 × 10¹, 1.3 × 10² and 1.2 × 10³ µGy/h, close to and higher than the benchmark for protection of ecosystems towards ionizing radiations of 10¹ µGy/h. Dose rates used in these studies were chosen to be in the 'derived consideration reference level' (DCRL) for gamma irradiation where deleterious effects can appear in freshwater fish. Also, these dose rates were similar to the ones already tested on tritium (beta ionizing radiation) in our previous work, in order to compare both types of ionizing radiation. Results showed that gamma irradiation did not induce any effect on survival and hatching. No effect was observed on DNA damages, but ROS production was increased. Muscle damages were observed for all tested dose rates, similarly to previous results obtained with tritium (beta ionizing radiation) at similar dose rates. Some molecular responses therefore appeared to be relevant for the study of gamma ionizing radiation effects in zebrafish.

Transforming Acute Ecotoxicity Data into Chronic Data: A Statistical Method to Better Inform the Radiological Risk for Nonhuman Species

Ecotoxicity data constitute the basic information to support the derivation of ecological benchmark values, whatever the stressor concerned. However, the set of appropriate data may be limited, especially with regard to chronic exposure conditions. The available data are often biased in favor of acute data from laboratory-controlled conditions, much easier to acquire. To make the best use of the available knowledge and better inform the effects of ionizing radiation chronic exposure on nonhuman species, we investigated the transposition to ionizing radiation ecotoxicity of one method proposed for chemicals to extrapolate chronic information from acute toxicity data. Such a method would contribute to enriching chronic data sets required for the derivation of benchmark values, making them more robust when used as reference values for ecological risk assessment. We developed accordingly the Acute to Chronic Transformation for Radiotoxicity data (ACTR) approach, which we validated. We introduced then the new concept of Endpoint Sensitivity Distribution (ESD). This finally allowed us to compare purely chronic and ACTR-built ESDs for different taxa. For some of them, the predicted and observed distributions looked very similar. This promising ACTR method appeared applicable with a reasonable level of confidence, but its generalization asks for improvements, some being already identified.

Ionising Radiation Induces Promoter DNA Hypomethylation and Perturbs Transcriptional Activity of Genes Involved in Morphogenesis during Gastrulation in Zebrafish

Embryonic development is particularly vulnerable to stress and DNA damage, as mutations can accumulate through cell proliferation in a wide number of cells and organs. However, the biological effects of chronic exposure to ionising radiation (IR) at low and moderate dose rates (< 6 mGy/h) remain largely controversial, raising concerns for environmental protection. The present study focuses on the molecular effects of IR (0.005 to 50 mGy/h) on zebrafish embryos at the gastrula stage (6 hpf), at both the transcriptomics and epigenetics levels. Our results show that exposure to IR modifies the expression of genes involved in mitochondrial activity from 0.5 to 50 mGy/h. In addition, important developmental pathways, namely, the Notch, retinoic acid, BMP and Wnt signalling pathways, were altered at 5 and 50 mGy/h. Transcriptional changes of genes involved in the morphogenesis of the ectoderm and mesoderm were detected at all dose rates, but were prominent from 0.5 to 50 mGy/h. At the epigenetic level, exposure to IR induced a hypomethylation of DNA in the promoter of genes that colocalised with both H3K27me3 and H3Kme4 histone marks and correlated with changes in transcriptional activity. Finally, pathway enrichment analysis demonstrated that the DNA methylation changes occurred in the promoter of important developmental genes, including morphogenesis of the ectoderm and mesoderm. Together, these results show that the transcriptional program regulating morphogenesis in gastrulating embryos was modified at dose rates greater than or equal to 0.5 mGy/h, which might predict potential neurogenesis and somitogenesis defects observed at similar dose rates later in development.

Radiocesium (137Cs) concentrations in the two-toed amphiuma (Amphiuma means) and the lesser siren (Siren intermedia)

This study sought to determine radiocesium (¹³⁷Cs) concentrations in two species of aquatic salamanders - the two-toed amphiuma (Amphiuma means) and the lesser siren (Siren intermedia) on the Savannah River Site. Concentrations (¹³⁷Cs Bq/g, dry wt) of the two species were similar at both ¹³⁷Cs-contaminated (A. means = 0.733 ± 0.242, n = 5; S. intermedia = 0.839 ± 0.722, n = 5) and reference sites (A. means = 0.028 ± 0.020, n = 5; S. intermedia = 0.042 ± 0.027, n = 11). Salamanders captured in areas impacted by ¹³⁷Cs contamination exhibited significantly higher ¹³⁷Cs concentrations than individuals captured at reference sites (U = 146, p < 0.001). Salamander size (snout-vent length) was not correlated with whole-body ¹³⁷Cs. An analysis of our data using the ERICA tool suggests that negative impacts due to ¹³⁷Cs exposure are unlikely in these species. Overall, these data indicate that A. means and S. intermedia inhabiting contaminated sites bioaccumulate but do not biomagnify ¹³⁷Cs.

Tritiated Water Exposure in Zebrafish (Danio rerio): Effects on the Early-Life Stages

Tritium, a radioactive isotope of hydrogen of natural and anthropogenic origin, is ubiquitously present in the environment. Effluents of nuclear centers of production are significant anthropogenic sources. With the upcoming project of thermonuclear fusion, tritium releases in the environment may increase. It is therefore important to characterize the ecological risk linked to tritium. The effects of tritiated water (HTO) were therefore studied in zebrafish larvae exposed for 10 d to different dose rates, 1.1 × 10² , 4.1 × 10² , and 3.8 × 10³  µGy/h for larvae corresponding, respectively, to a water contamination of 10⁴ , 10⁵ , and 10⁶  Bq/mL of HTO. Those dose rates were higher than 10 μGy/h, which is the threshold recommended to start monitoring ecosystems where radiological contaminants are present. Mortality, embryo-larval development, immune toxicity, genotoxicity, neurotoxicity, and alterations of tissues were investigated. The results showed that HTO exposure induced DNA damage and reactive oxygen species production and modulated the expression of genes involved in detoxification processes. Moreover, modifications of the muscular tissues (degradation of myofibrils at 4 d post fertilization and disorganization of mitochondria at later stages) were observed. The results differed with HTO dose rates and with developmental stages. These results will drive future research for the development of new HTO-sensitive biomarkers and will allow us to progress in the characterization of the modes of action of tritium in fish. Environ Toxicol Chem 2020;39:648-658. © 2019 SETAC.

Effects of in vivo exposure to tritium: a multi-biomarker approach using the fathead minnow, Pimephales promelas

Tritium (³H) is a radioactive isotope of hydrogen. In the environment, the most common form of tritium is tritiated water (HTO). However, tritium can also be incorporated into organic molecules, forming organically bound tritium (OBT). The present study characterized the effects of tritium on the health of the fathead minnow, Pimephales promelas. Fish were exposed to a gradient of HTO (activity concentrations of 12,000, 25,000, and 180,000 Bq/L) and OBT using food spiked with tritiated amino acids (OBT only, with an activity concentration of 27,000 Bq/L). A combined exposure condition where fish were placed in 25,000 Bq/L water and received OBT through feed was also studied. Fish were exposed for 60 days, followed by a 60-day depuration period. A battery of health biomarkers were measured in fish tissues at seven time points throughout the 120 days required to complete the exposure and depuration phases. HTO and OBT were also measured in fish tissues at the same time points. Results showed effects of increasing tritium activity concentrations in water after 60 days of exposure. The internal dose rates of tritium, estimated from the tissue free-water tritium (TFWT) and OBT activity concentrations, reached a maximum of 0.65 μGy/h, which is relatively low considering background levels. No effects were observed on survival, fish condition, and metabolic indices (gonado-, hepato-, and spleno-somatic indexes (GSI, HSI, SSI), RNA/DNA and proteins/DNA ratios). Multivariate analyses showed that several biomarkers (DNA damages, micronucleus frequency, brain acetylcholinesterase, lysosomal membrane integrity, phagocytosis activity, and reactive oxygen species production) were exclusively correlated with fish tritium internal dose rate, showing that tritium induced genotoxicity, as well as neural and immune responses. The results were compared with another study on the same fish species where fish were exposed to tritium and other contaminants in natural environments. Together with the field study, the present work provides useful data to identify biomarkers for tritium exposure and better understand modes of action of tritium on the fathead minnow.

Is non-human species radiosensitivity in the lab a good indicator of that in the field? Making the comparison more robust

Ecological risk assessment has globally become the basis for environmental decision-making within government and industry for chemical substances. Regarding radioactive substances, recently revised International and European Basic Safety Standards are pushing the development of member state policy on environmental regulation in the field of radiological protection. Within this framework, existing derived effect benchmarks for ionising radiation and non-human species need to be more robust to reinforce their credibility when used as levels of exposure considered to be safe for the environment. Actually, the derivation of such benchmarks has mainly relied on laboratory studies from a limited number of species. Moreover lab species would be apparently less radiosensitive than for example terrestrial wildlife chronically exposed to ionising radiation in the Chernobyl Exclusion Zone. Additionally to the results of such comparison that still need to be confirmed, another way to challenge benchmarks is to improve the quality/quantity of radiotoxicity data constituting the basis for a statistically-based comparison. This is the major focus of this paper where we demonstrate through various examples how to make the comparison more robust (i) by analysing the discrepancy between lab and field at the taxonomic level rather than at the ecosystem level, (ii) by extending the knowledge base making use of acute radiotoxicity data, (iii) by identifying environmental factors modifying radiological dose-effect relationship in the field.

The importance of deriving adequate wildlife benchmark values to optimize radiological protection in various environmental exposure situations

The actions to be taken to demonstrate that the environment is adequately protected against the detrimental effects of ionising radiation, and if needed to protect it, must be commensurate with the overall level of risk to non-human biota. To judge the level of risk, the estimated dose rates absorbed by animals and plants need to be compared with dose criteria, a benchmark or reference value. A variety of aspects will influence the final value of the derived benchmark, including: the aim of the application of the benchmark, the protection goals of the assessment, the data on radiation-induced biological effects considered, and the methodology used. Benchmark values have been proposed by several international organizations (UNSCEAR, ICRP, IAEA), countries (USA, Canada) and research projects (ERICA, PROTECT), for different application purposes and protection goals and using a variety of methodologies. This paper describes the aspects that need to be considered in the derivation of numerical benchmarks, the approaches used by different organizations and the benchmark values they have proposed for the radiation protection of the environment. The benchmark values proposed are compared with the dose-rates at which radiation-induced biological effects have been described in animals and plants.

Higher than … or lower than ….? Evidence for the validity of the extrapolation of laboratory toxicity test results to predict the effects of chemicals and ionising radiation in the field

Single species laboratory tests and associated species sensitivity distributions (SSDs) that utilise the resulting data can make a key contribution to efforts to prospective hazard assessments for pesticides, biocides, metals and ionising radiation for research and regulatory risk assessment. An assumption that underlies the single species based toxicity testing approach when combined in SSD models is that the assessments of sensitivities to chemical and ionising radiation measured across a range of species in the laboratory can inform on the likely effects on communities present in the field. Potential issues with the validity of this assumption were already recognised by Van Straalen and Denneman (1989) in their landmark paper on the SSD methodology. In this work, they identified eight major factors that could potentially compromise the extrapolation of laboratory toxicity data to the field. Factors covered a range of issues related to differences in chemistry (e.g. bioavailability, mixtures); environmental conditions (optimal, variable), ecological (compensatory, time-scale) and population genetic structure (adaptation, meta-population dynamics). This paper outlines the evidence pertaining to the influence of these different factors on toxicity in the laboratory as compared to the field focussing especially on terrestrial ecosystems. Through radiological and ecotoxicological research, evidence of the influence of each factor on the translation of observed toxicity from the laboratory to field is available in all cases. The importance of some factors, such as differences in chemical bioavailability between laboratory tests and the field and the ubiquity of exposure to mixtures is clearly established and has some relevance to radiological protection. However, other factors such as the differences in test conditions (optimal vs sub-optimal) and the development of tolerance may be relevant on a case by case basis. When SSDs generated from laboratory tests have been used to predict chemical and ionising radiation effects in the field, results have indicated that they may often seem to under-predict impacts, although this may also be due to other factors such as the effects of other non-chemical stressors also affecting communities at polluted sites. A better understanding of the main factors affecting this extrapolation can help to reduce uncertainty during risk assessment.

Adverse effects induced by chronic gamma irradiation in progeny of adult fish not affecting parental reproductive performance

Multigenerational studies have become of great interest in ecotoxicology since the consequence of parental exposure to contaminants on offspring generations was established in situ or in laboratory conditions. The present study mainly examined the chronic effects of external Cs-137 gamma irradiation exposure at 4 dose rates (control, 0.5, 5, and 50 mGy h^-1 ) on adult zebrafish (F0) exposed for 10 d and their progeny (F1) exposed or unexposed for 4 to 5 d. The main endpoints investigated included parental reproductive performance, embryo-larval survival, DNA alterations, and reactive oxygen species (ROS) production in F0 and F1. No effects on reproductive success, fecundity, or egg fertilization rate were observed. However, drastic effects were observed on F1 exposed to 50 mGy h^-1 , resulting in a mortality rate of 100%. The drastic effects were also observed when the progeny was not irradiated. It was demonstrated that the sensitivity of the embryos was mainly attributable to parental irradiation. Moreover, these drastic effects induced by adult irradiation disappeared over time when 10 d-irradiated adults were placed in a nonirradiated condition. Alterations in larval DNA were observed for the 3 dose rates, and an increase of ROS production was also shown for the 2 lowest dose rates. The present study improves our understanding of the consequences of parental exposure conditions to the progeny. Furthermore, it provides an incentive to take transmitted generational effects into account in ecological risk assessments. Environ Toxicol Chem 2019;38:2556-2567. © 2019 SETAC.

Differential modification of the C. elegans proteome in response to acute and chronic gamma radiation: Link with reproduction decline

Emission of ionizing radiation (IR) in the environment is a natural phenomenon which can be enhanced by human activities. Ecosystems are then chronically exposed to IR. But environmental risk assessment of chronic exposure suffers from a lack of knowledge. Extrapolation of data from acute to chronic exposure is not always relevant, and can lead to uncertainties as effects could be different between the two irradiation modes, especially regarding reproduction endpoint, which is an ecologically relevant parameter. In the present study, we decided to refine the understanding of the molecular mechanisms involved in response to acute and chronic γ-irradiation by a global proteome label free LC-MS/MS analysis. C. elegans were exposed to 3 common cumulated radiation doses for acute or chronic exposure condition and global modification of the proteome was studied. This analysis of protein expression has demonstrated the modulation of proteins involved in regulatory biological processes such as lipid transport, DNA replication, germ cell development, apoptosis, ion transport, cuticle development, and aging at lower doses than those for which individual effects on reproduction have been previously observed. Thus, these proteins could constitute early and sensitive markers of radio-induced reprotoxicity; more specifically HAT-1, RPS-19 in acute and VIT-3 for chronic conditions that are expressed in a dose-dependent manner. Finally, to focus on reproduction process, this analysis showed either repression or overexpression of 12 common proteins in organisms exposed to acute or chronic irradiation, respectively. These proteins include the vitellogenin cluster notably involved in lipid transport and oocyte maturation and proteins involved in cuticle development and molting i.e. COL-14, GLF-1, NOAH-1, NOAH-2, ACN-1. These results show that protein expression modulation is a sensitive and predictive marker of radio-induced reproductive effects, but also highlight limitation of data extrapolation from acute to chronic exposure for environmental risk assessment.

Physiological effects of gamma irradiation in the honeybee, Apis mellifera

Terrestrial ecosystems are exposed to various kinds of pollutants, including radionuclides. The honeybee, Apis mellifera, is commonly used in ecotoxicology as a model species for evaluating the effects of pollutants. In the present study, honeybees were irradiated right after birth for 14 days with gamma rays at dose rates ranging between 4.38 × 10^-3 and 588 mGy/d. Biological tissues (head, intestine and abdomen) were sampled at D3, D10 and D14. Ten different physiological markers involved in nervous (acetylcholinesterase (AChE)), antioxidative (catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione-S-transferase (GST)), immune system (phenoloxidase (PO)) and metabolism (carboxylesterases (CaEs) and alkaline phosphatase (ALP)) were measured. Univariate analyses were conducted to determine whether each individual biomarker response was positively or negatively correlated with the dose rate. Then, multivariate analyses were applied to investigate the relationships between all the biomarker responses. Although no mortality occurred during the experiment, several biomarkers varied significantly in relation to the dose rate. Globally, the biomarkers of antioxidant and immune systems decreased as the dose rate increased. Reversible effects on the indicator of the neural system were found. Concerning indicators of metabolism (carboxylesterases), variations occurred but no clear pattern was found. Taken altogether, these results help better understand the effects of ionizing radiation on bees by identifying relevant physiological markers of effects. These results could improve the assessment of the environmental risk due to ionizing radiation in terrestrial ecosystems.

A single indicator of noxiousness for people and ecosystems exposed to stable and radioactive substances

Inspired by methods used for life cycle impact assessment (LCIA), we constructed a series of indicators to appreciate the noxiousness of radioactive materials and wastes for human and ecosystem health. According to known potential human health and ecological effects of such materials, six main impact categories were considered to initiate the development of the method: human cancer and non-cancer effects vs. ecotoxicity, considering both chemotoxicity and radiotoxicity. For ecosystems, the noxiousness indicator is based on the concept of Potentially Affected Fraction (PAF), used as a damage indicator at the ecosystem level. The PAF express the toxic pressure on the environment due to one substance. It has been enlarged to mixtures of substances as multi-substances PAF (ms-PAF), and applied to a mix of stable and radioactive substances. Combining ecotoxicity data and a simplified model of exposure of fauna and flora, we proposed a chemotoxicity indicator and a radiotoxicity indicator, ultimately aggregated into a single indicator simply by addition. According to acknowledged practices in LCIA and corresponding available data, we suggested implementing to human health an approach similar to that applied to ecosystems. We produced eigth basic indicators combining effects categories (cancer and non cancer), exposure pathways (ingestion and inhlation) and substances (chemicals and radionuclides). The principle of additivity supporting the whole proposed approach allows their complete aggregation into a single indicator also for human health. Different source terms may be then easily directly compared in terms of human and ecological noxiousness. Applied to the time evolution of a High Level radioactive Waste (HLW), the method confirmed over 1 million years the dominance of the radiotoxicity in the noxiousness of the material for both humans and environment. However there is a change with time in the ranking of the most noxious substances, with stable metals contribution going progressively up. Finally, the HLW global noxiousness, integrating human health and ecological aspects, was assessed through time at three stages and showed a temporal decrease as expected from the dominance of the radiotoxicity.

Modeling species richness and abundance of phytoplankton and zooplankton in radioactively contaminated water bodies

Water bodies polluted by the Mayak nuclear plant in Russia provide valuable information on multi-generation effects of radioactive contamination on freshwater organisms. For example, lake Karachay was probably the most radioactive lake in the world: its water contained ∼2 × 10⁷ Bq/L of radionuclides and estimated dose rates to plankton exceeded 5 Gy/h. We performed quantitative modeling of radiation effects on phytoplankton and zooplankton species richness and abundance in Mayak-contaminated water bodies. Due to collinearity between radioactive contamination, water body size and salinity, we combined these variables into one (called HabitatFactors). We employed a customized machine learning approach, where synthetic noise variables acted as benchmarks of predictor performance. HabitatFactors was the only predictor that outperformed noise variables and, therefore, we used it for parametric modeling of plankton responses. Best-fit model predictions suggested 50% species richness reduction at HabitatFactors values corresponding to dose rates of 10⁴-10⁵ μGy/h for phytoplankton, and 10³-10⁴ μGy/h for zooplankton. Under conditions similar to those in lake Karachay, best-fit models predicted 81-98% species richness reductions for various taxa (Cyanobacteria, Bacillariophyta, Chlorophyta, Rotifera, Cladocera and Copepoda), ∼20-300-fold abundance reduction for total zooplankton, but no abundance reduction for phytoplankton. Rotifera was the only taxon whose fractional abundance increased with contamination level, reaching 100% in lake Karachay, but Rotifera species richness declined with contamination level, as in other taxa. Under severe radioactive and chemical contamination, one species of Cyanobacteria (Geitlerinema amphibium) dominated phytoplankton, and rotifers from the genus Brachionus dominated zooplankton. The modeling approaches proposed here are applicable to other radioecological data sets. The results provide quantitative information and easily interpretable model parameter estimates for the shapes and magnitudes of freshwater plankton responses to a wide range of radioactive contamination levels.

ALLIANCE perspectives on integration of humans and the environment into the system of radiological protection

Risks posed by the presence of radionuclides in the environment require an efficient, balanced, and adaptable assessment for protecting exposed humans and wildlife, and managing the associated radiological risk. Exposure of humans and wildlife originate from the same sources releasing radionuclides to the environment. Environmental concentrations of radionuclides serve as inputs to estimate the dose to man, fauna, and flora, with transfer processes being, in essence, similar, which calls for a common use of transport models. Dose estimates are compared with the radiological protection criteria for humans and wildlife, such as those developed by the International Commission on Radiological Protection. This indicates a similarity in the approaches for impact assessment in humans and wildlife, although some elements are different (e.g. the protection endpoint for humans is stochastic effects on individuals, whereas for wildlife, it is deterministic effects on species and ecosystems). Human and environmental assessments are consistent and complementary in terms of how they are conducted and in terms of the underlying databases (where appropriate). Not having an integrated approach may cause difficulties for operators and regulators, for communication to stakeholders, and may even hamper decision making. For optimised risk assessment and management, the impact from non-radiation contaminants and stressors should also be considered. Both in terms of the underlying philosophy and the application via appropriate tools, the European Radioecology Alliance (ALLIANCE) upholds that integration of human and ecological impact and risk assessment is recommended from several perspectives (e.g. chemical/radiological risks).

It Is Time to Move Beyond the Linear No-Threshold Theory for Low-Dose Radiation Protection

The US Environmental Protection Agency (USEPA) is the primary federal agency responsible for promulgating regulations and policies to protect people and the environment from ionizing radiation. Currently, the USEPA uses the linear no-threshold (LNT) model to estimate cancer risks and determine cleanup levels in radiologically contaminated environments. The LNT model implies that there is no safe dose of ionizing radiation; however, adverse effects from low dose, low-dose rate (LDDR) exposures are not detectable. This article (1) provides the scientific basis for discontinuing use of the LNT model in LDDR radiation environments, (2) shows that there is no scientific consensus for using the LNT model, (3) identifies USEPA reliance on outdated scientific information, and (4) identifies regulatory reliance on incomplete evaluations of recent data contradicting the LNT. It is the time to reconsider the use of the LNT model in LDDR radiation environments. Incorporating the latest science into the regulatory process for risk assessment will (1) ensure science remains the foundation for decision making, (2) reduce unnecessary burdens of costly cleanups, (3) educate the public on the real effects of LDDR radiation exposures, and (4) harmonize government policies with the rest of the radiation scientific community.

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.

Tritiated water exposure disrupts myofibril structure and induces mis-regulation of eye opacity and DNA repair genes in zebrafish early life stages

Tritium (³H) is a radioactive isotope of hydrogen. In the environment, the most common form of tritium is tritiated water (HTO). The present study aimed to identify early biomarkers of HTO contamination through the use of an aquatic model, the zebrafish (Danio rerio). We used the zebrafish embryo-larvae model to investigate the modes of action of HTO exposure at dose rates of 0.4 and 4 mGy/h, dose rates expected to induce deleterious effects on fish. Zebrafish were exposed to HTO from 3 hpf (hours post fertilization) to 96 hpf. The transcriptomic effects were investigated 24 h and 96 h after the beginning of the contamination, using mRNAseq. Results suggested an impact of HTO contamination, regardless of the dose rate, on genes involved in muscle contraction (tnnt2d, tnni2a.4, slc6a1a or atp2a1l) and eye opacity (crygm2d9, crygmxl1, mipb or lim2.3) after 24 h of contamination. Interestingly, an opposite differential expression was highlighted in genes playing a role in muscle contraction and eye opacity in 24 hpf embryos when comparing dose rates, suggesting an onset of DNA protective mechanisms. The expression of h2afx and ddb2 involved in DNA repair was enhanced in response to HTO exposure. The entrainment of circadian clock and the response to H₂O₂ signalling pathways were enriched at 96 hpf at 0.4 mGy/h and in both stages after 4 mGy/h. Genes involved in ROS scavenging were differentially expressed only after 24 h of exposure for the lowest dose rate, suggesting the onset of early protective mechanisms against oxidative stress. Effects highlighted on muscle at the molecular scale were confirmed at a higher biological scale, as electron microscopy observations revealed sarcomere impairments in 96 hpf larvae for both dose rates. Together with other studies, the present work provides useful data to better understand modes of action of tritium on zebrafish embryos-larvae.

Radiosensitivity and transgenerational effects in non-human species

The ALLIANCE working group on effects of ionising radiation on wildlife brings together European researchers to work on the topics of radiosensitivity and transgenerational effects in non-human biota. Differences in radiation sensitivity across species and phyla are poorly understood, but have important implications for understanding the overall effects of radiation and for radiation protection; for example, sensitive species may require special attention in monitoring and radiation protection, and differences in sensitivity between species also lead to overall effects at higher levels (community, ecosystem), since interactions between species can be altered. Hence, understanding the mechanisms of interspecies radiation sensitivity differences may help to clarify mechanisms underpinning intraspecies variation. Differences in sensitivity may only be revealed when organisms are exposed to ionising radiation over several generations. This issue of potential long-term or hereditary effects for both humans and wildlife exposed to low doses of ionising radiation is a major concern. Animal and plant studies suggest that gamma irradiation can lead to observable effects in the F1 generation that are not attributable to inheritance of a rare stable DNA mutation. Several studies have provided evidence of an increase in genomic instability detected in germ or somatic cells of F1 organisms from exposed F0 organisms. This can lead to induced radiosensitivity, and can result in phenotypic effects or lead to reproductive effects and teratogenesis. In particular, studies have been conducted to understand the possible role of epigenetic modifications, such as DNA methylation, histone modifications, or expression of non-coding RNAs in radiosensitivity, as well as in adaptation effects. As such, research using biological models in which the relative contribution of genetic and epigenetic processes can be elucidated is highly valuable.

Population sensitivities of animals to chronic ionizing radiation-model predictions from mice to elephant

Model predictions of population response to chronic ionizing radiation (endpoint 'morbidity') were made for 11 species of warm-blooded animals, differing in body mass and lifespan - from mice to elephant. Predictions were made also for 3 bird species (duck, pigeon, and house sparrow). Calculations were based on analytical solutions of the mathematical model, simulating a population response to low-LET ionizing radiation in an ecosystem with a limiting resource (Sazykina, Kryshev, 2016). Model parameters for different species were taken from biological and radioecological databases; allometric relationships were employed for estimating some parameter values. As a threshold of decreased health status in exposed populations ('health threshold'), a 10% reduction in self-repairing capacity of organisms was suggested, associated with a decline in ability to sustain environmental stresses. Results of the modeling demonstrate a general increase of population vulnerability to ionizing radiation in animal species of larger size and longevity. Populations of small widespread species (mice, house sparrow; body mass 20-50 g), which are characterized by intensive metabolism and short lifespan, have calculated 'health thresholds' at dose rates about 6.5-7.5 mGy day^-1. Widespread animals with body mass 200-500 g (rat, common pigeon) - demonstrate 'health threshold' values at 4-5 mGy day^-1. For populations of animals with body mass 2-5 kg (rabbit, fox, raccoon), the indicators of 10% health decrease are in the range 2-3.4 mGy day^-1. For animals with body mass 40-100 kg (wolf, sheep, wild boar), thresholds are within 0.5-0.8 mGy day^-1; for herbivorous animals with body mass 200-300 kg (deer, horse) - 0.5-0.6 mGy day^-1. The lowest health threshold was estimated for elephant (body mass around 5000 kg) - 0.1 mGy day^-1. According to the model results, the differences in population sensitivities of warm-blooded animal species to ionizing radiation are generally depended on the metabolic rate and longevity of organisms, also on individual radiosensitivity of biological tissues. The results of 'health threshold' calculations are formulated as a graded scale of wildlife sensitivities to chronic radiation stress, ranging from potentially vulnerable to more resistant species. Further studies are needed to expand the scale of population sensitivities to radiation, including other groups of wildlife - cold-blooded species, invertebrates, and plants.

Effects of in situ exposure to tritiated natural environments: A multi-biomarker approach using the fathead minnow, Pimephales promelas

Aquatic ecosystems are chronically exposed to radionuclides as well as other pollutants. Increased concentrations of pollutants in aquatic environments can present a risk to exposed organisms, including fish. The goal of this study was to characterize the effects of tritium, in the context of natural environments, on the health of fathead minnow, Pimephales promelas. Fish were exposed to tritium (activity concentrations ranging from 2 to 23,000Bq/L) and also to various concentrations of several metals to replicate multiple-stressor environments. Fish were exposed for 60days, then transferred to the tritium background site where they stayed for another 60days. Tritium, in the forms of tritiated water (HTO) and organically bound tritium (OBT), and a series of fish health indicators were measured in fish tissues at seven time points throughout the 120days required to complete the exposure and the depuration phases. Results showed effects of environmental exposure following the increase of tritium activity and metals concentrations in water. The internal dose rates of tritium, estimated from tissue HTO and OBT activity concentrations, were consistently low (maximum of 0.2μGy/h) compared to levels at which population effects may be expected (>100μGy/h) and no effects were observed on survival, fish condition, gonado-somatic, hepato-somatic, spleno-somatic and metabolic indices (RNA/DNA, proteins/DNA and protein carbonylation (in gonads and kidneys)). Using multivariate analyses, we showed that several biomarkers (DNA damages, MN frequency, gamma-H2AX, SFA/MUFA ratios, lysosomal membrane integrity, AChE, SOD, phagocytosis and esterase activities) were exclusively correlated with fish tritium internal dose rate, showing that tritium induced genotoxicity, DNA repair activity, changes in fatty acid composition, and immune, neural and antioxidant responses. Some biomarkers were responding to the presence of metals, but overall, more biomarkers were linked to internalized tritium. The results are discussed in the context of multiple stressors involving metals and tritium.

Ecological risk assessment of mixtures of radiological and chemical stressors: Methodology to implement an msPAF approach

A main challenge in ecological risk assessment is to account for the impact of multiple stressors. Nuclear facilities can release both radiological and chemical stressors in the environment. This study is the first to apply species sensitivity distribution (SSD) combined with mixture models (concentration addition (CA) and independent action (IA)) to derive an integrated proxy of the ecological impact of combined radiological and chemical stressors: msPAF (multisubstance potentially affected fraction of species). The approach was tested on the routine liquid effluents from nuclear power plants that contain both radioactive and stable chemicals. The SSD of ionising radiation was significantly flatter than the SSD of 8 stable chemicals (namely Cr, Cu, Ni, Pb, Zn, B, chlorides and sulphates). This difference in shape had strong implications for the selection of the appropriate mixture model: contrarily to the general expectations the IA model gave more conservative (higher msPAF) results than the CA model. The msPAF approach was further used to rank the relative potential impact of radiological versus chemical stressors.

Parental gamma irradiation induces reprotoxic effects accompanied by genomic instability in zebrafish (Danio rerio) embryos

Gamma radiation represents a potential health risk to aquatic and terrestrial biota, due to its ability to ionize atoms and molecules in living tissues. The effects of exposure to ⁶⁰Co gamma radiation in zebrafish (Danio rerio) were studied during two sensitive life stages: gametogenesis (F0: 53 and 8.7mGy/h for 27 days, total doses 31 and 5.2Gy) and embryogenesis (9.6mGy/h for 65h; total dose 0.62Gy). Progeny of F0 exposed to 53mGy/h showed 100% mortality occurring at the gastrulation stage corresponding to 8h post fertilization (hpf). Control and F0 fish exposed to 8.7mGy/h were used to create four lines in the first filial generation (F1): control, G line (irradiated during parental gametogenesis), E line (irradiated during embryogenesis) and GE line (irradiated during parental gametogenesis and embryogenesis). A statistically significant cumulative mortality of GE larva (9.3%) compared to controls was found at 96 hpf. E line embryos hatched significantly earlier compared to controls, G and GE (48-72 hpf). The deformity frequency was higher in G and GE, but not E line compared to controls at 72 hpf. One month after parental irradiation, the formation of reactive oxygen species (ROS) was increased in the G line, but did not significantly differ from controls one year after parental irradiation, while at the same time point it was significantly increased in the directly exposed E and GE lines from 60 to 120 hpf. Lipid peroxidation (LPO) was significantly increased in the G line one year after parental irradiation, while significant increase in DNA damage was detected in both the G and GE compared to controls and E line at 72 hpf. Radiation-induced bystander effects, triggered by culture media from tissue explants and observed as influx of Ca²⁺ ions through the cellular membrane of the reporter cells, were significantly increased in 72 hpf G line progeny one month after irradiation of the parents. One year after parental irradiation, the bystander effects were increased in the E line compared to controls, but not in progeny of irradiated parents (G and GE lines). Overall, this study showed that irradiation of parents can result in multigenerational oxidative stress and genomic instability in irradiated (GE) and non-irradiated (G) progeny of irradiated parents, including increases in ROS formation, LPO, DNA damage and bystander effects. The results therefore highlight the necessity for multi- and transgenerational studies to assess the environmental impact of gamma radiation.

Dose-dependent effects of gamma radiation on the early zebrafish development and gene expression

Ionizing radiation from natural sources or anthropogenic activity has the potential to cause oxidative stress or genetic damage in living organisms, through the ionization and excitation of molecules and the subsequent production of free radicals and reactive oxygen species (ROS). The present work focuses on radiation-induced biological effects using the zebrafish (Danio rerio) vertebrate model. Changes in developmental traits and gene expression in zebrafish were assessed after continuous external gamma irradiation (0.4, 3.9, 15 and 38 mGy/h) with corresponding controls, starting at 2.5 hours post fertilization (hpf) and lasting through embryogenesis and the early larval stage. The lowest dose rate corresponded to recommended benchmarks at which adverse effects are not expected to occur in aquatic ecosystems (2-10 mGy/day). The survival observed at 96 hours post fertilization (hpf) in the 38 mGy/h group was significantly lower, while other groups showed no significant difference compared to controls. The total hatching was significantly lower from controls in the 15 mGy/h group and a delay in hatching onset in the 0.4 mGy/h group was observed. The deformity frequency was significantly increased by prolonged exposure duration at dose rates ≥ 0.4 mGy/h. Molecular responses analyzed by RNA-seq at gastrulation (5.5 hpf transcriptome) indicate that the radiation induced adverse effects occurred during the earliest stages of development. A dose-response relationship was found in the numbers of differentially regulated genes in exposure groups compared to controls at a total dose as low as 1.62 mGy. Ingenuity Pathway Analysis identified retinoic acid receptor activation, apoptosis, and glutathione mediated detoxification signaling as the most affected pathways in the lower dose rate (0.54 mGy/h), while eif2 and mTOR, i.e., involved in the modulation of angiogenesis, were most affected in higher dose rates (5.4 and 10.9 mGy/h). By comparing gene expression data, myc was found to be the most significant upstream regulator, followed by tp53, TNF, hnf4a, TGFb1 and cebpa, while crabp2b and vegfab were identified as most frequent downstream target genes. These genes are associated with various developmental processes. The present findings show that continuous gamma irradiation (≥ 0.54 mGy/h) during early gastrula causes gene expression changes that are linked to developmental defects in zebrafish embryos.

Influence of long-term chronic exposure and weather conditions on Scots pine populations

Over a period of 8 years (2007-2014), we were evaluating seed quality and morphological abnormalities in Scots pine trees affected as a result of the Chernobyl accident. The calculated dose rates for the trees at the study sites varied from background values at the reference sites to 40 mGy/year at the most contaminated site. We investigated whether radioactive contamination and/or weather factors could decrease the reproductive capacity or increase the frequency of morphological abnormalities of needles in pine trees. Scots pine seeds are characterized by high interannual variability of viability, which is largely determined by weather conditions. No consistent differences in reproductive capacity were detected between the impacted and reference populations. Brachyblasts with three needles were found only in the affected populations; however, their frequency was very low and only at the very border of significance at the p < 0.10 level.

Impact of the Fukushima accident on marine biota, five years later

In a previous commentary written in 2011 in the aftermath of the Fukushima accident in Japan, I summarized what was then understood about the effects of accidental radioactive discharges to marine life and forecasted into the future how the marine environment would likely be affected. Since that time, several studies have been conducted on the impact of the accident on marine organisms, and radiation doses arising thereof. I developed a dynamic transfer model for studying the bioaccumulation of Fukushima radionuclides in marine biota and assessed the impact and likelihood of effects to marine life. In the present article, I highlight the lessons learned over the past 5 years. I address whether the environmental consequences in the marine environment are as significant as initially feared and, with respect to the current situation, what remains to be investigated as the radioactivity continues to spread in the marine environment. Integr Environ Assess Manag 2016;12:654-658. © 2016 SETAC.

Radiation dose estimation for marine mussels following exposure to tritium: Best practice for use of the ERICA tool in ecotoxicological studies

Accurate dosimetry is critically important for ecotoxicological and radioecological studies on the potential effects of environmentally relevant radionuclides, such as tritium ((3)H). Previous studies have used basic dosimetric equations to estimate dose from (3)H exposure in ecologically important organisms, such as marine mussels. This study compares four different methods of estimating dose to adult mussels exposed to 1 or 15 MBq L(-1) tritiated water (HTO) under laboratory conditions. These methods were (1) an equation converting seawater activity concentrations to dose rate with fixed parameters; (2) input into the ERICA tool of seawater activity concentrations only; (3) input into the ERICA tool of estimated whole organism concentrations (woTACs), comprising dry activity plus estimated tissue free water tritium (TFWT) activity (TFWT volume × seawater activity concentration); and (4) input into the ERICA tool of measured whole organism activity concentrations, comprising dry activity plus measured TFWT activity (TFWT volume × TFWT activity concentration). Methods 3 and 4 are recommended for future ecotoxicological experiments as they produce values for individual animals and are not reliant on transfer predictions (estimation of concentration ratio). Method 1 may be suitable if measured whole organism concentrations are not available, as it produced results between 3 and 4. As there are technical complications to accurately measuring TFWT, we recommend that future radiotoxicological studies on mussels or other aquatic invertebrates measure whole organism activity in non-dried tissues (i.e. incorporating TFWT and dry activity as one, rather than as separate fractions) and input this data into the ERICA tool.

Population modelling to compare chronic external radiotoxicity between individual and population endpoints in four taxonomic groups

In this study, we modelled population responses to chronic external gamma radiation in 12 laboratory species (including aquatic and soil invertebrates, fish and terrestrial mammals). Our aim was to compare radiosensitivity between individual and population endpoints and to examine how internationally proposed benchmarks for environmental radioprotection protected species against various risks at the population level. To do so, we used population matrix models, combining life history and chronic radiotoxicity data (derived from laboratory experiments and described in the literature and the FREDERICA database) to simulate changes in population endpoints (net reproductive rate R0, asymptotic population growth rate λ, equilibrium population size Neq) for a range of dose rates. Elasticity analyses of models showed that population responses differed depending on the affected individual endpoint (juvenile or adult survival, delay in maturity or reduction in fecundity), the considered population endpoint (R0, λ or Neq) and the life history of the studied species. Among population endpoints, net reproductive rate R0 showed the lowest EDR10 (effective dose rate inducing 10% effect) in all species, with values ranging from 26 μGy h(-1) in the mouse Mus musculus to 38,000 μGy h(-1) in the fish Oryzias latipes. For several species, EDR10 for population endpoints were lower than the lowest EDR10 for individual endpoints. Various population level risks, differing in severity for the population, were investigated. Population extinction (predicted when radiation effects caused population growth rate λ to decrease below 1, indicating that no population growth in the long term) was predicted for dose rates ranging from 2700 μGy h(-1) in fish to 12,000 μGy h(-1) in soil invertebrates. A milder risk, that population growth rate λ will be reduced by 10% of the reduction causing extinction, was predicted for dose rates ranging from 24 μGy h(-1) in mammals to 1800 μGy h(-1) in soil invertebrates. These predictions suggested that proposed reference benchmarks from the literature for different taxonomic groups protected all simulated species against population extinction. A generic reference benchmark of 10 μGy h(-1) protected all simulated species against 10% of the effect causing population extinction. Finally, a risk of pseudo-extinction was predicted from 2.0 μGy h(-1) in mammals to 970 μGy h(-1) in soil invertebrates, representing a slight but statistically significant population decline, the importance of which remains to be evaluated in natural settings.

Dose-Response Analysis Using R

Dose-response analysis can be carried out using multi-purpose commercial statistical software, but except for a few special cases the analysis easily becomes cumbersome as relevant, non-standard output requires manual programming. The extension package drc for the statistical environment R provides a flexible and versatile infrastructure for dose-response analyses in general. The present version of the package, reflecting extensions and modifications over the last decade, provides a user-friendly interface to specify the model assumptions about the dose-response relationship and comes with a number of extractors for summarizing fitted models and carrying out inference on derived parameters. The aim of the present paper is to provide an overview of state-of-the-art dose-response analysis, both in terms of general concepts that have evolved and matured over the years and by means of concrete examples.

External gamma irradiation-induced effects in early-life stages of zebrafish, Danio rerio

In the general context of validation of tools useful for the characterization of ecological risk linked to ionizing radiation, the effects of an external gamma irradiation were studied in zebrafish larvae irradiated for 96 h with two dose rates: 0.8 mGy/d, which is close to the level recommended to protect ecosystems from adverse effects of ionizing radiation (0.24 mGy/d) and a higher dose rate of 570 mGy/d. Several endpoints were investigated, such as mortality, hatching, and some parameters of embryo-larval development, immunotoxicity, apoptosis, genotoxicity, neurotoxicity and histological alterations. Results showed that an exposure to gamma rays induced an acceleration of hatching for both doses and a decrease of yolk bag diameter for the highest dose, which could indicate an increase of global metabolism. AChE activity decreased with the low dose rate of gamma irradiation and alterations were also shown in muscles of irradiated larvae. These results suggest that gamma irradiation can induce damages on larval neurotransmission, which could have repercussions on locomotion. DNA damages, basal ROS production and apoptosis were also induced by irradiation, while ROS stimulation index and EROD biotransformation activity were decreased and gene expression of acetylcholinesterase, choline acetyltransferase, cytochrome p450 and myeloperoxidase increased. These results showed that ionizing radiation induced an oxidative stress conducting to DNA damages. This study characterized further the modes of action of ionizing radiation in fish.

Radiological dose reconstruction for birds reconciles outcomes of Fukushima with knowledge of dose-effect relationships

We reconstructed the radiological dose for birds observed at 300 census sites in the 50-km northwest area affected by the accident at the Fukushima Daiichi nuclear power plant over 2011–2014. Substituting the ambient dose rate measured at the census points (from 0.16 to 31 μGy h⁻¹) with the dose rate reconstructed for adult birds of each species (from 0.3 to 97 μGy h⁻¹), we confirmed that the overall bird abundance at Fukushima decreased with increasing total doses. This relationship was directly consistent with exposure levels found in the literature to induce physiological disturbances in birds. Among the 57 species constituting the observed bird community, we found that 90% were likely chronically exposed at a dose rate that could potentially affect their reproductive success. We quantified a loss of 22.6% of the total number of individuals per increment of one unit log₁₀-tansformed total dose (in Gy), over the four-year post-accident period in the explored area. We estimated that a total dose of 0.55 Gy reduced by 50% the total number of birds in the study area over 2011–2014. The data also suggest a significant positive relationship between total dose and species diversity.