The fate of radionuclides in the environment is a cause of great concern for modern society, seen especially in 2011 after the Fukushima accident. Among the environmental compartments, seawater covers most of the earth's surface and may be directly or indirectly impacted. The interaction between radionuclides and the marine compartment is therefore essential for better understanding the transfer mechanisms from the hydrosphere to the biosphere. This information allows for the evaluation of the impact on humans via our interaction with the biotope that has been largely undocumented up to now. In this report, we attempt to make a link between the speciation of heavy elements in natural seawater and their uptake by a model marine organism. More specifically, because the interaction of actinides with marine invertebrates has been poorly studied, the accumulation in a representative member of the Mediterranean coralligenous habitat, the sponge Aplysina cavernicola, was investigated and its uptake curve exposed to a radiotracer (241)Am was estimated using a high-purity Ge gamma spectrometer. But in order to go beyond the phenomenological accumulation rate, the speciation of americium(III) in seawater must be assessed. The speciation of (241)Am (and natural europium as its chemically stable surrogate) in seawater was determined using a combination of different techniques: Time-Resolved Laser-Induced Fluorescence (TRLIF), Extended X-ray Absorption Fine Structure (EXAFS) at the LIII edge, Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) and the resulting data were compared with the speciation modeling. In seawater, the americium(III) complex (as well as the corresponding europium complex, although with conformational differences) was identified as a ternary sodium biscarbonato complex, whose formula can be tentatively written as NaAm(CO3)2·nH2O. It is therefore this chemical form of americium that is accumulated by the sponge A. cavernicola.

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In case of a nuclear event, contamination (broad or limited) of the population or of specific workers might occur. In such a senario, the fate of actinide contaminants may be of first concern, in particular with regard to human target organs like the skeleton. To improve our understanding of the toxicological processes that might take place, a mechanistic approach is necessary. For instance, ∼50% of Pu(IV) is known from biokinetic data to accumulate in bone, but the underlining mechanisms are almost unknown. In this context, and to obtain a better description of the toxicological mechanisms associated with actinides(IV), we have undertaken the investigation, on a molecular scale, of the interaction of thorium(IV) with osteopontin (OPN) a hyperphosphorylated protein involved in bone turnover. Thorium is taken here as a simple model for actinide(IV) chemistry. In addition, we have selected a phosphorylated hexapeptide (His-pSer-Asp-Glu-pSer-Asp-Glu-Val) that is representative of the peptidic sequence involved in the bone interaction. For both the protein and the biomimetic peptide, we have determined the local environment of Th(IV) within the bioactinidic complex, combining isothermal titration calorimetry, attenuated total reflectance Fourier transform infrared spectroscopy, theoretical calculations with density functional theory, and extended X-ray absorption fine structure spectroscopy at the Th LIII edge. The results demonstrate a predominance of interaction of metal with the phosphate groups and confirmed the previous physiological studies that have highlighted a high affinity of Th(IV) for the bone matrix. Data are further compared with those of the uranyl case, representing the actinyl(V) and actinyl(VI) species. Last, our approach shows the importance of developing simplified systems [Th(IV)-peptide] that can serve as models for more biologically relevant systems.

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A radiochemical separation is presented for americium, plutonium and neptunium from sediment samples by using an unique anionic exchange process. An oxidation-reduction step was introduced in the classical procedure of the radiochemical determination of transuranic elements in order to control the valence of the separated elements.

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Rationale Radiation therapy is widely used for cancer treatment but its efficacy is limited by radioresistance and by damages caused to adjacent normal tissues. Active research aims at maximizing tumor eradication while reducing side-effects with theranostic nanoparticles that act as radioenhancers in situ. Ferromagnetic materials have been identified as promising nanotools for image-guided radiotherapy. Here, we investigated the potential of RGD-tagged magnetosomes (magnetosomes@RGD), bacterial biogenic magnetic nanoparticles naturally coated by a biological membrane and genetically engineered to express a RGD peptide, as tumour enhancers to conventional radiotherapy and proton therapy. Methods The potential of native and RGD-functionalized magnetosomes to enhance the effects of ionizing radiations was assessed in a DNA fragmentation assay and in melanoma and colorectal cancer cells using in vitro clonogenic assays. The in vivo radiotherapy enhancement efficacy of the magnetosomes@RGD was explored in preclinical models of melanoma-bearing mice treated with either X-rays or protons. Results Native and RGD-tagged magnetosomes similarly enhanced radiation-induced DNA damage. On cancer cells, both magnetoprobes were able to boost the killing efficacy of radiotherapy, although to a much larger extent with the magnetosomes@RGD enhancing the mortality by 2.5 fold in melanoma cells and by 2.9 fold in colorectal cancer cells. In vivo treatment of melanomabearing mice with magnetosomes@RGD prior to X-rays led to a 65% reduction in tumor development compared to radiotherapy alone (31%). Comparatively, a more effective tumor 3 growth inhibition (77%) was observed in combining RGD-decorated nanoprobes to proton therapy. The radioenhancing potential of magnetosomes@RGD was further evidenced by the DNA damage observed in the nanoscale vicinity of magnetosomes within the treated lesions. Conclusions Our results show efficacy of magnetosomes functionalized with a RGD peptide as tumor radioenhancers to both X-rays and protons in vivo and strengthen the interest of developing biogenic magnetoparticles for multimodal nanomedicine for cancer therapy.

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