IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 104 NOM and Aquatic Systems Thursday, 27 August 2026 / Hall C loadings and Stern–Volmer constants. SHAP (SHapley Additive exPlanations) values were used to identify the molecular descriptors that most strongly drive each fluorescence endmember and its metal-binding affinity. The four endmembers comprised one marine humic-like, two terrestrial humiclike, and one protein-like component.[2] CMTF and SHAP analyses consistently linked the strongly Eu³⁺-binding terrestrial humic-like endmember to highly oxygenated, aromatic CRAMlike molecules with elevated AI moₔ and O/C, while the weakly binding marine humic-like endmember was associated with aliphatic, lower-O compounds consistent with a connate-water origin. UO2²⁺ showed binding patterns that diverged from Eu³⁺, highlighting metalspecific molecular selectivity. The combined data fusion–ML pipeline thus provides a transferable, interpretable framework for connecting spectroscopic signatures and molecular composition of deep groundwater DOM to its role in radionuclide transport and supports more mechanistic safety assessment of HLW geological disposal. References 1. Saito, T. et al. Environ. Sci. Processes & Impacts 17, 1386–1395 (2015). 2. Saito, T., et al. ACS EST Water 3, 4103–4112 (2023). 3. Schenker, C., et al. IEEE J. Sel. Top. Signal Process. 15, 506–521 (2020). Acknowledgement This work was supported by the Japan Atomic Energy Agency (JAEA) Horonobe Underground Research Center and JSPS KAKENHI. We thank the Japan Advanced Institute of Science and Technology (JAIST) for FT-ICR-MS access.
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