Technology-critical elements (TCEs) are increasingly introduced into aquatic environments due to their extensive use in modern technologies, however, their behaviour in marine systems remains poorly understood, particularly under climate change conditions. This project aims to elucidate behaviour of TCEs in estuarine environments, focusing on water-column processes and interactions with sediment and biota using advanced analytical approaches for their speciation/fractionation and process-oriented environmental studies. Size fractionation will be performed by filtration and partial ultrafiltration, potentially bioavailable fractions will be assessed using diffusive gradients in thin films, while determination of organically-bound TCEs will be performed using solid-phase extraction. TCEs quantification will be carried out using ICP-MS and voltammetric analysis. Asymmetric flow field-flow fractionation and size exclusion chromatography coupled to ICP-MS will be additionally explored. Detailed characterisation of dissolved organic matter and key physicochemical parameters will support interpretation of TCEs-organic interactions.Relying on validated analytical protocols, process studies will address TCEs’ responses to climate-related stressors. The Krka River estuary will serve as a natural analogue, complemented by controlled laboratory and microcosm experiments. Sediment-water boundary exchanges will be studied through diffusive flux measurements and sediment forced resuspension experiments. Biological implications will be investigated through phytoplankton community responses under realistic TCEs exposure scenarios.Experimentally derived speciation data will be compared with speciation models, enabling evaluation and potential refinement of parameters for estuarine applications. The project will deliver quality-assured data and process-based insights into TCEs behaviour under climate change, supporting improved environmental risk assessment and monitoring strategies.