Generation of time series of environmental quantities is a tool to explore the dynamic nature of the physical phenomenon that manifests in these quantities. In the radiometric context, this includes investigation of the notoriously complicated dynamic of radon in various environmental media, of ambient dose rate or following radiologically relevant events such as the passage of contaminated clouds and fallout after the Chernobyl and Fukushima accidents. The objectives are detection, quantification and classification of “signals” contained in the series, or the “volume” of an event that has caused the signal. The former is typical for tracer studies and studies intended to understand the physical nature of a process, the latter for quantifying radiological impact. Importantly, also the observation process, i.e., measuring, induces variability that has to be accounted for.

More often than not the phenomena or processes to be assessed are variable in time and space. One is interested in both – the temporal aspect to assess its evolution and the spatial one for mapping or to assess the regionally different evolution. Sometimes surveys are performed with moving monitors which entails the additional task to disentangle the two variability components. For example, in surveys of ambient dose rate by moving G-M monitors one has to consider that the dose rate changes with fluctuation of cosmic radiation or ambient radon concentration that in turn are subject to temporal changes.

Methodologies for assessing spatial and temporal variability are different. Here we are interested in the temporal aspect in the first place. If the task consists in identifying signals and understanding the epistemic chain from their generators over their propagation in the environment to the observation process, the task consists in decomposing the series. Components may be a constant or stationary background, a trend, periodic and aperiodic fluctuation in different time scales, instrumental noise and statistical noise due to the stochastic nature of a process. Mathematical procedures are available to separate the components, such as low/high pass filtering, Fourier, autocorrelation and Hurst analyses. Phase space exploration can serve to investigate the complexity of a process; chaotic analysis can indicate its predictability. Some examples derived from radon time series are shown. Also examples of observational variability are given.

As examples of studies that consider spatio-temporal effects, we address ground-borne surveys of ambient dose rate, geographical transects of outdoor radon concentration (now possible with simple, easily transportable radon monitors) and ambient dose rate measurements after Chernobyl and Fukushima. A novel project targeting possible differences of the radon dynamic in different climatic zones (temperate, Mediterranean, tropical) is currently in its initial stage.

The interaction between ionizing radiation and the human microbiota presents a dual challenge in modern oncology. While radiotherapy is a primary treatment modality, it frequently induces systemic dysbiosis, compromising patient health. Concurrently, the rise of multidrug-resistant (MDR) bacterial infections in immunocompromised patients necessitates faster, high-precision diagnostic tools. This work explores the pivotal role of metal-complexed small molecules, metabolites and metallophores, in both protecting commensal bacteria and detecting pathogenic threats. The work presented herein is the result of a multidisciplinary study from two projects, integrating coordination chemistry, microbiology, and molecular imaging.

On TrypGut we intended to address the radioprotective potential of the tryptophan metabolite 8-hydroxyquinoline-2-carboxylic acid (8-HQA) and its metal complexes. Inactivation kinetics were performed on individual and co-cultured human microbiota isolates (e.g., Actinomyces viscosus) exposed to ionizing radiation. Preliminary results demonstrate a significant radioprotective effect of the Ga3+/8-HQA complex on A. viscosus, with evidence of a symbiotic survival advantage in oral co-culture models compared to individual assays. This suggests that specific metabolites can preserve the structural integrity of the microbiome during radiotherapy.

Parallelly, on SuperOpTyMe project our focus is the synthesis and chemical speciation of radiolabeled opine-type metallophores (OpTyMe) designed to exploit bacterial metal-uptake pathways for selective PET imaging of MDR infections.

By leveraging the chemical properties of metal-ligand complexes, we can transition toward a "theranostic" microbial strategy. While 8-HQA-based complexes offer a path to mitigating radiotherapy-induced dysbiosis, optimized OpTyMe probes provide the precision required to identify and monitor resistant infections.

Beside the natural sources of radiation present throughout the environment, human activities, nuclear weapons testing and major nuclear accidents such as those occurred at Chernobyl in 1986 and Fukushima in 2011, have introduced additional radioactive materials into the environment and increased environmental radiation levels, traces of which can still be detected today.

Radioactive substances released into the atmosphere during the Chernobyl accident were widely dispersed and mostly settled across the land areas of Europe. In contrast, about 80% of the atmospheric releases from the Fukushima Daiichi nuclear disaster spread over and were deposited in the Pacific Ocean. As a result, the impact on human populations, in terms of radiation exposure and health effects, was significantly lower than in cases where contamination occurs over land (UNSCEAR 2020/2021 Report).

This paper presents an overview and assessment of radioactivity in environment in the Republic of Serbia, four decades after the Chernobyl nuclear accident and fifteen years after Fukushima Daiichi nuclear disaster. The study examines long-term trends in radionuclide activity concentrations in key environmental compartments including air, soil, water, and food products. Particular attention is given to the persistence of artificial radionuclides especially ¹³⁷Cs, which remains the dominant anthropogenic contributor in radioactivity. In addition to ¹³⁷Cs, nuclear accidents release other artificial radionuclides in atmosphere. One of the particular biological importance is ⁹⁰Sr. It is mainly taken into the human body through ingestion especially via milk and dairy products. Due to its chemical similarity to calcium, ⁹⁰Sr tends to accumulate in bones, where its concentration in the human body is the highest. Tritium (³H) is also an important radionuclide released during nuclear accidents. It is typically found in the form of tritiated water (HTO), which easily mixes with natural water and can enter the human body through drinking water, food, and inhalation.

Monitoring data collected over several decades indicate decline in radioactive concentrations due to radioactive decay and environmental processes such as migration dilution and fixation in soil layers. Current activity levels are generally within regulatory limits and do not pose a significant risk to human health or the environment. Radioactivity monitoring in the Republic of Serbia is regulated, among other regulations, by the Rulebook on the Establishment of a Programme for Systematic Environmental Radioactivity Assessment (Official Gazette of RS, No. 100/2010).

Results of radioactivity monitoring in the Republic of Serbia were previously presented in the monograph Chernobyl – 30 Years After, 2016 ( https://dzz.org.rs). Here, we provide updated findings after forty years of continuous monitoring, including the impacts of the Chernobyl accident and the Fukushima Daiichi nuclear disaster. These data highlight the importance of ongoing environmental surveillance and provide an overview of artificial radioactivity trends over four decades.

Keywords: radioactivity monitoring, environment, Chernobyl, Fukushima, artificial radionuclides

Acknowledgments: The research presented in this paper was done with financial support of the Ministry of Science, Technological Development and Innovation of the Republic of Serbia, within the funding of scientific research work at the University of Belgrade, Vinča Institute of Nuclear Sciences (Contract No. 451-03-33/2026-03/ 200017)

In the past few years, theranostic radiopharmaceuticals targeting the Prostate-Specific Membrane Antigen (PSMA) opened new avenues for the treatment and management of prostate cancer (PCa). In particular, a variety of PSMA inhibitors were labelled with different imaging and therapeutic radionuclides, leading to the development of the β ^- emitting ¹⁷⁷Lu-PSMA-617 (Pluvicto), approved by the FDA and EMA for targeted radionuclide therapy of PSMA-positive metastatic castration-resistant PCa (mCRPC). More recently, ¹⁶¹Tb started to be considered a promising therapeutic radionuclide and an attractive alternative to ¹⁷⁷Lu. ¹⁶¹Tb is a β ^- emitter but also emits conversion electrons and Auger electrons (AE) and thus is expected to allow a combined beta and AE therapy with improved therapeutic index, particularly for disseminated cancer disease. AEs show a high linear energy transfer over a nanometric range. Thus, the specific targeting of highly radiosensitive organelles in tumoral cells, like the nucleus or the mitochondria, might enhance the therapeutic effects of AEs at lower administered doses, while minimizing undesirable side effects. Having this in mind, we have embarked on the study of dual-targeted ¹⁶¹Tb-radiocomplexes, carrying a PSMA derivative and acridine orange (AO) or triphenyl phosphonium (TPP) groups to promote selective uptake by PCa cells and accumulation in the nucleus or mitochondria, respectively. The study was also extended to congener complexes with the AE emitter ¹¹¹In.

In this communication, we describe the preclinical evaluation of the above mentioned dual-targeted radiocomplexes in cellular and animal models of PCa, aiming to assess their interest as PCa radiotheranostics. These dual-targeted radiocomplexes were obtained with DOTA-based chelators carrying PSMA and AO and TPP derivatives. Their in vitro biological evaluation included cellular uptake, internalization and PSMA-blocking studies in PSMA-positive PC3 PIP and PSMA-negative PC3 FLU cells, nuclear and mitochondrial uptake studies, and assessment of radiobiological effects (e.g., clonogenic survival and gamma-H2AX assays). µSPECT/CT imaging studies in mice with PSMA-positive PCa xenografts were also performed for selected ¹⁶¹Tb- and ¹¹¹In-complexes. The designed dual-targeted ¹⁶¹Tb- and ¹¹¹In-radiocomplexes had a favourable biological performance, showing high and specific cellular uptake and internalization in PSMA-positive PCa cell lines, and higher radiotoxicity than the corresponding single target complexes ¹⁶¹Tb- and ¹¹¹In-PSMA-617. Our results highlight the potential of the devised dual-targeted strategy to optimize the biological performance of radiotheranostics for Auger therapy of cancer.