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.

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.

Unusual evolution of tree frog populations in the Chernobyl exclusion zone.

Despite the ubiquity of pollutants in the environment, their long-term ecological consequences are not always clear and still poorly studied. This is the case concerning the radioactive contamination of the environment following the major nuclear accident at the Chernobyl nuclear power plant. Notwithstanding the implications of evolutionary processes on the population status, few studies concern the evolution of organisms chronically exposed to ionizing radiation in the Chernobyl exclusion zone. Here, we examined genetic markers for 19 populations of Eastern tree frog (Hyla orientalis) sampled in the Chernobyl region about thirty years after the nuclear power plant accident to investigate microevolutionary processes ongoing in local populations. Genetic diversity estimated from nuclear and mitochondrial markers showed an absence of genetic erosion and higher mitochondrial diversity in tree frogs from the Chernobyl exclusion zone compared to other European populations. Moreover, the study of haplotype network permitted us to decipher the presence of an independent recent evolutionary history of Chernobyl exclusion zone's Eastern tree frogs caused by an elevated mutation rate compared to other European populations. By fitting to our data a model of haplotype network evolution, we suspected that Eastern tree frog populations in the Chernobyl exclusion zone have a high mitochondrial mutation rate and small effective population sizes. These data suggest that Eastern tree frog populations might offset the impact of deleterious mutations because of their large clutch size, but also question the long-term impact of ionizing radiation on the status of other species living in the Chernobyl exclusion zone.

Involvement of phospholipids in resistance and adaptation of Escherichia coli to acid conditions and to long-term survival.

In Escherichia coli membranes, three major phospholipids are formed: phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and cardiolipin (CL). We report here the survival of mutants lacking either PE or both PG and CL at an acid pHo and during long-term survival experiments. Stationary phase cultures of E. coli lacking PE are much more sensitive to acid shock (pHo 3) than the wild-type strain. Moreover, in the strain lacking PE, long-term survival in stationary phase is impaired and after 5 days no viable cells are recovered. The survival of an exponential phase culture to acid shock is known to be increased if the culture is exposed to moderately acid conditions (pHo 5) prior to a shift to pHo 3. If either PE or both PG and CL are missing, the exposure to pHo 5 does not increase the survival at pHo 3.

Analysis of the effect exerted by extracellular pH on the maltose regulon in Escherichia coli K-12.

The Escherichia coli maltose regulon consists of five operons under the control of the MalT transcriptional activator. lac operon fusions were constructed in vitro with the MalT-dependent promoter and with the malT promoter itself. beta-Galactosidase activity displayed by these fusions during growth at different external pH (pHo) revealed that growth at a pHo higher than 6 stimulates the transcription of malT- and MalT-controlled genes in the absence or presence of maltose. Using a malTp1 malTp10 promoter that is cAMP-CRP (cAMP receptor protein)-independent, it was demonstrated that CRP is essential for malT pHo regulation and that the pHo-dependent activity of malKp is a direct consequence of malT regulation. The pHo regulation displayed by a deleted but still functional malT promoter fused to lacZ demonstrates that this minimal promoter contains all the regulatory regions for establishing pHo regulation. In the absence of MIc, a repressor of malT expression, the pHo regulation of malT was still effective. It is proposed that binding of cAMP-CRP at malTp may be affected by malTp topology induced by pHo or that a pHo-dependent effector may act in concert with the cAMP-CRP complex.