ONE-BLUE will provide an integrated assessment of contaminants of emerging concern (CECs) and their impacts, will develop new monitoring tools, and will provide an advanced understanding of the combined effects of CECs and climate change (CC) on the different marine ecosystems and their biodiversity. The following objectives are defined: • Improve the current knowledge of the concentrations, profiles, fate, behaviour, and effects of CECs, in the different marine compartments and ecosystems through three case studies (Atlantic and Arctic oceans and the Mediterranean Sea) and develop safety guidelines and protocols for future CECs monitoring in marine ecosystems. • Provide an advanced understanding of possible interaction between CC and CECs in marine ecosystems with studies under controlled conditions in marine mesocosms. • Develop a database (DB), the CECsMarineDB, following FAIR principles, with a database management system (DBMS) to collect the data generated in ONE-BLUE and capitalize data from other projects and existing DBs. A graphical user interface (GUI) will be developed and used for data exploration and demonstration of the fate and behaviour of CECs in a changing environment. • Provide new solutions in support of the implementation of relevant EU policies; (i) a series of new approach methodologies (NAMs) to improve the ecotoxicity assessment of CECs in marine ecosystems; (ii) a tiered effect-directed approaches (EDA) combining toxicological assessment and chemical analysis; (iii) an advanced ultrasonic system for sampling and enrichment micro/nanoplastics from seawater; (iv) a remote autonomous sensor to assess CECs in marine waters in quasi-real-time; a decision support system (DSS) based on machine and deep learning strategies to assess and forecast combined effects of CC and CECs in marine ecosystems. • Disseminate the project results and establish the exploitation plan for the developed technologies.