Uranium and Neptunium Accumulation by the Byssus of <i>Mytilus galloprovincialis</i>

Marine mussel byssus is recognized for its capacity to accumulate trace metals from seawater including metallic radionuclides. This study deals with uranium and neptunium, two actinides involved in the electronuclear cycle. We propose to elucidate the underlying molecular mechanisms at the origin of uranium and neptunium uptake by the byssus threads of mussel using model systems of increasing molecular complexity: PEG–DOPA (4‐arm polyethylene glycol–dihydroxyphenylalanine), purified mfp‐1 (mussel foot protein‐1), and native byssus. Ex vivo sorption isotherms display a linear adsorption behavior at environmentally relevant concentrations, reflected in high uranium concentration factors that emphasize the byssus as an efficient passive accumulator. Extended X‐ray absorption fine structure analysis showed that uranium (uranyl(VI)) coordinates through oxygen donors ligands, consistent with chelation by catechols in mfp‐1 and byssus. X‐ray absorption near edge structure (XANES) confirmed that uranyl(VI) remained unreduced in all systems. For neptunium (neptunyl(V)), UV–Vis–NIR spectra and XANES both revealed partial reduction of neptunyl(V) to Np(IV) in the presence of mfp‐1 , while PEG–DOPA induced no such reduction, suggesting the presence of redox‐active moieties in the mfp‐1 . These findings advance our understanding of uranium and neptunium accumulation in mussel byssus, highlighting the central role of mfps and their catechol‐rich domains in selective and redox‐active actinide binding.