Integration of ecosystem science into radioecology: A consensus perspective

Ionizing radiation induces neurotoxicity in Xenopus laevis embryos through neuroactive ligand-receptor interaction pathway

Ionizing radiation (IR) poses a significant threat to both the natural environment and biological health. Exposure to specific doses of ionizing radiation early in an organism's development can lead to developmental toxicity, particularly neurotoxicity. Through experimentation with Xenopus laevis (X. laevis), we examined the effects of radiation on early developmental stage. Our findings revealed that radiation led to developmental abnormalities and mortality in X. laevis embryos in a dose-dependent manner, disrupting redox homeostasis and inducing cell apoptosis. Additionally, radiation caused neurotoxic effects, resulting in abnormal behavior and neuron damage in the embryos. Further investigation into the underlying mechanisms of radiation-induced neurotoxicity indicated the potential involvement of the neuroactive ligand-receptor interaction pathway, which was supported by RNA-Seq analysis. Validation of gene expression associated with this pathway and analysis of neurotransmitter levels confirmed our hypothesis. In addition, we further validated the important role of this signaling pathway in radiation-induced neurotoxicity through edaravone rescue experiments. This research establishes a valuable model for radiation damage studying and provides some insight into radiation-induced neurotoxicity mechanisms.

Evolutionary approach for pollution study: The case of ionizing radiation

Estimating the consequences of environmental changes, specifically in a global change context, is essential for conservation issues. In the case of pollutants, the interest in using an evolutionary approach to investigate their consequences has been emphasized since the 2000s, but these studies remain rare compared to the characterization of direct effects on individual features. We focused on the study case of anthropogenic ionizing radiation because, despite its potential strong impact on evolution, the scarcity of evolutionary approaches to study the biological consequences of this stressor is particularly true. In this study, by investigating some particular features of the biological effects of this stressor, and by reviewing existing studies on evolution under ionizing radiation, we suggest that evolutionary approach may help provide an integrative view on the biological consequences of ionizing radiation. We focused on three topics: (i) the mutagenic properties of ionizing radiation and its disruption of evolutionary processes, (ii) exposures at different time scales, leading to an interaction between past and contemporary evolution, and (iii) the special features of contaminated areas called exclusion zones and how evolution could match field and laboratory observed effects. This approach can contribute to answering several key issues in radioecology: to explain species differences in the sensitivity to ionizing radiation, to improve our estimation of the impacts of ionizing radiation on populations, and to help identify the environmental features impacting organisms (e.g., interaction with other pollution, migration of populations, anthropogenic environmental changes). Evolutionary approach would benefit from being integrated to the ecological risk assessment process.

Bioaccumulation of contaminants in Scarabaeidae and Silphidae beetles at sites polluted by coal combustion residuals and radiocesium

Anthropogenic contamination from coal-fired power plants and nuclear reactors is a pervasive issue impacting ecosystems across the globe. As a result, it is critical that studies continue to assess the accumulation and effects of trace elements and radionuclides in a diversity of biota. In particular, bioindicator species are a powerful tool for risk assessment of chemically contaminated habitats. Using inductively coupled plasma mass spectrometry (ICP-MS) and auto-gamma counting, we analyzed trace element and radiocesium contaminant concentrations in Scarabaeidae and Silphidae beetles (Order: Coleoptera), important taxa in decomposition and nutrient cycling, at contaminated and reference sites on the Savannah River Site, South Carolina, U.S. Our results revealed variability in trace element concentrations between Scarabaeidae and Silphidae beetles at uncontaminated and contaminated sites. Compared to Scarabaeidae, Silphidae had higher levels of chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), and zinc (Zn). Unexpectedly, concentrations of Cr, Cu, and Ni were higher in both taxa at the uncontaminated sites. Scarabaeidae and Silphidae beetles at the coal combustion waste site consistently had high concentrations of arsenic (As), and Scarabaeidae had high concentrations of selenium (Se). Of the 50 beetles analyzed for radiocesium levels, two had elevated radioactivity concentrations, both of which were from a site contaminated with radionuclides. Our results suggest carrion beetles may be particularly sensitive to bioaccumulation of contaminants due to their trophic position and role in decomposition, and thus are useful sentinels of trace element and radionuclide contamination.

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.

Radionuclide contamination in Canada: A scoping review

Radionuclides were first discovered in the late 1800s, and artificial (anthropogenic) radionuclides in the 1930s. Since then, this group of substances has been increasingly incorporated into various peaceful and non-peaceful applications across Canada and the world, bringing with it both advanced technological and medical benefits, and public concern about the dangers from radiation exposure. As such, a breadth of research on, and monitoring of, radionuclides in the Canadian environment has been generated, the results of which span decades. However, a recent comprehensive review of these is not readily available. This study aims to fill this gap by synthesizing available literature from the last 30 years on the Canadian state and provenance of radionuclide contamination to better understand the context of overall sources and status of contamination. The findings indicate that while regional and temporal variations exist, on average, routine radionuclide exposure in Canada is generally attributed mainly to natural sources and fallout from historical nuclear weapons testing and nuclear accidents (including the Chernobyl and Fukushima power plant accidents) and to a smaller degree to emissions from nuclear facilities, including active and historical uranium mines and mills, nuclear research facilities, and nuclear power plants. Levels of anthropogenic radionuclides in the Canadian environment have declined since the initial cessation of nuclear weapons testing in the 1960s and are generally below guidelines protective of human health. On the national scale, present-day nuclear sector facilities do not appear to be a significant source of routine anthropogenic, nor technically-enhanced naturally occurring radionuclide exposure, though local scenarios may vary. These findings contribute context for evaluating the sustainable management of nuclear technologies, radioactive materials and waste in Canada and globally, in line with UN Sustainable Development Goal 12 and target 12.4: responsible management of chemicals and waste.

Ionizing radiation affects the demography and the evolution of Caenorhabditis elegans populations

Ionizing radiation can reduce survival, reproduction and affect development, and lead to the extinction of populations if their evolutionary response is insufficient. However, demographic and evolutionary studies on the effects of ionizing radiation are still scarce. Using an experimental evolution approach, we analyzed population growth rate and associated change in life history traits across generations in Caenorhabditis elegans populations exposed to 0, 1.4, and 50.0 mGy.h^-1 of ionizing radiation (gamma external irradiation). We found a higher population growth rate in the 1.4 mGy.h^-1 treatment and a lower in the 50.0 mGy.h^-1 treatment compared to the control. Realized fecundity was lower in both 1.4 and 50.0 mGy.h^-1 than control treatment. High irradiation levels decreased brood size from self-fertilized hermaphrodites, specifically early brood size. Finally, high irradiation levels decreased hatching success compared to the control condition. In reciprocal-transplant experiments, we found that life in low irradiation conditions led to the evolution of higher hatching success and late brood size. These changes could provide better tolerance against ionizing radiation, investing more in self-maintenance than in reproduction. These evolutionary changes were with some costs of adaptation. This study shows that ionizing radiation has both demographic and evolutionary consequences on populations.

Male frequency in Caenorhabditis elegans increases in response to chronic irradiation

Outcrossing can be advantageous in a changing environment because it promotes the purge of deleterious mutations and increases the genetic diversity within a population, which may improve population persistence and evolutionary potential. Some species may, therefore, switch their reproductive mode from inbreeding to outcrossing when under environmental stress. This switch may have consequences on the demographic dynamics and evolutionary trajectory of populations. For example, it may directly influence the sex ratio of a population. However, much remains to be discovered about the mechanisms and evolutionary implications of sex ratio changes in a population in response to environmental stress. Populations of the androdioecious nematode Caenorhabditis elegans, are composed of selfing hermaphrodites and rare males. Here, we investigate the changes in the sex ratio of C. elegans populations exposed to radioactive pollution for 60 days or around 20 generations. We experimentally exposed populations to three levels of ionizing radiation (i.e., 0, 1.4, and 50 mGy.h^-1). We then performed reciprocal transplant experiments to evaluate genetic divergence between populations submitted to different treatments. Finally, we used a mathematical model to examine the evolutionary mechanisms that could be responsible for the change in sex ratio. Our results showed an increase in male frequency in irradiated populations, and this effect increased with the dose rate. The model showed that an increase in male fertilization success or a decrease in hermaphrodite self-fertilization could explain this increase in the frequency of males. Moreover, males persisted in populations after transplant back into the control conditions. These results suggested selection favoring outcrossing under irradiation conditions. This study shows that ionizing radiation can sustainably alter the reproductive strategy of a population, likely impacting its long-term evolutionary history. This study highlights the need to evaluate the impact of pollutants on the reproductive strategies of populations when assessing the ecological risks.

Conceptualization of arid region radioecology strategies for agricultural ecosystems of the United Arab Emirates (UAE)

Since the last decade, ambitious nuclear power programmes have begun maturing in the Arab countries, most importantly in the United Arab Emirates (UAE). The region's environment and population, therefore, are prone to adverse, long-term impacts of radionuclide discharges. To calculate the associated exposure scenarios, to estimate doses and their consequences, and finally, to lay out a radiological emergency management plan, arid region radioecology is taking shape in the UAE as a major field of research. Geography, demography, food habits, weather, soil, water, flora, and fauna of the desert-marine regions are quite distinct from their temperate counterparts. This results in the need to increase the knowhows of environmental migration and bioaccumulation of radionuclides in the region's agricultural ecosystems. In this paper, we present a detailed review of the measured data from the UAE and nearby nations, generating insights for the soil radioactivity and soil-to-plant transfer phenomena under local arid conditions. In the literature, the radionuclide activity concentrations (in Bq kg^-1) vary over five orders of magnitude depending on nuclide type, sample type, and locality. Variabilities over six orders of magnitude are observed for transfer parameters too, and in-depth studies on the transfer mechanisms are usually scarce. We discuss the recent progresses made in root and foliar uptake studies with methods relatively new to sandy soils, like controlled potting, and soil K_d measurements. Showing the serious gaps in the data and interpretations, we provide a justification for the immediate experimentation in the understudied aspects of radioecology in the UAE and in arid lands in general.

Environmental Chemistry of Radionuclides : Open Questions and Perspectives

Since the discovery of nuclear fission, atomic energy has become for mankind a source of energy, but it has also become a source of consternation. This Perspective presents and discusses the methodological evolution of the work performed in the radiochemistry laboratory that is part of the Institut de Chimie de Nice (France). Most studies in radioecology and environmental radiochemistry have intended to assess the impact and inventory of very low levels of radionuclides in specific environmental compartments. But chemical mechanisms at the molecular level remain a mystery because it is technically impossible (due to large dilution factors) to assess speciation in those systems. Ultra-trace levels of contamination and heterogeneity often preclude the use of spectroscopic techniques and the determination of direct speciation data, thus forming the bottleneck of speciation studies. The work performed in the Nice radiochemistry laboratory underlines this effort to input speciation data (using spectroscopic techniques like X ray Absorption Spectroscopy) in environmental and radioecological metrics.

Assessment of internal radiation exposure to Antarctic biota due to selected natural radionuclides in terrestrial and marine environment

The present article introduces data on natural radioactivity (⁴⁰K, ^230,232Th, ^234,238U) in the Antarctic marine and terrestrial environment. Various biota samples were analysed due to internal exposure to ⁴⁰K, ^230,232Th, ^234,238U. Activity concentration of ⁴⁰K was the highest in both marine and terrestrial samples. Mean values of ⁴⁰K activity concentration are 1340 Bq/kg and 370 Bq/kg for the marine and terrestrial samples respectively. ²³⁴U/²³⁸U ratios analysis revealed that sea waters and sea spray are the main source of the uranium in the terrestrial samples. Average ^230,232Th, ^234,238U activity concentrations in the Antarctic biota do not exceed 6 Bq/kg. Weighted internal dose rates are relatively low; they range from approximately 0.1 to 0.6 μGy/h. Statistically significant differences in radionuclide accumulation were discovered between the mosses and lichens. It may point to various mechanisms of the nutrient absorption from the environment by these organisms.

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.