One of the main risks of CCS (Carbon Capture and Storage) is CO 2 leakage from a storage site. The influence of CO 2 leakage on trace metals leaching from contaminated marine sediment in a potential storage area (Northern Spain) is addressed using standardized leaching tests. The influence of the pH of the leaching solution on the leachates is evaluated using deionized water, natural seawater and acidified seawater at pH = 5, 6 and 7, obtained by CO 2 bubbling. Equilibrium leaching tests ( EN 12457) were performed at different liquid–solid ratios and the results of ANC/BNC leaching test ( CEN/TS 15364) were modeled using Visual Minteq. Equilibrium tests gave values of the final pH for all seawater leachates between 7 and 8 due to the high acid neutralization capacity of the sediment. Combining leaching test results and geochemical modeling provided insight in the mechanisms and prediction of trace metals leaching in acidified seawater environment. ► Tier structured approach for assessment of the release of metals from sediment. ► Leaching test as useful tool to evaluate risks of a CCS site due to CO 2 leakages. ► Prediction of metal release from marine sediment in contact to acidified seawater. ► Metal and DOC release in equilibrium leaching tests as function of L/S ratio and pH. ► Geochemical modeling of chemical species release from contaminated sediment. Metal mobility from contaminated sediment under CO 2 leakages in CCS sites using leaching tests.