Platinum group elements (PGE) have significantly accumulated in heavily urban and industrial regions and the potential risks of aquatic pollution with PGE and their compounds must be reckoned with. However, studies of contamination and geochemical behavior of PGE in the Tagus estuary are scarce. Only few works were published in this case and PGE in porewaters is inexistent. Thus, further investigation is needed to assess these emergent pollutants cycling. This work aims to quantify PGE and to identify the major processes responsible for partition, speciation, bioavailability, transport and fate of PGE in the Tagus estuary. It also aims to quantify their fluxes between sediment and water, to understand the role of salt-marsh vegetation in PGE mobility and to elaborate a conceptual model of the PGE cycling. Overall, the obtained results will contribute to better understand PGE biogeochemistry and cycling in the aquatic environment, and expects to provide a baseline tool to implement in policy initiatives.