| Summary: | The aim of the report is three-fold. Firstly, to evaluate to what extent phase-out of certain per- and polyfluoroalkyl substances (PFAS) first initiated in the early 2000s are reflected in the biota concentration within the Baltic Sea. Secondly, to investigate the spatial differences of PFAS across the Baltic Sea, which has not previously been evaluated, and couple these results to PFAS observations in other matrices to better understand the flow of PFAS through the Baltic Sea ecosystem. Lastly, to investigate the implication of a proposed PFAS EQS dossier on the evaluation of Good Environmental Status in the Baltic Sea. We use data on PFAS from the Swedish Monitoring Program for Contaminants in Marine Biota covering 40 years for the longest time series (four Time Trend Stations) and 26 stations at present day. The program covers stations from the Bothnian Bay in the north to Skagerrak at the Swedish west coast (referred to as the Greater Baltic Sea) and PFAS is analyzed in four fish species and three bird species. The target compounds are perfluoroalkyl sulfonic acid (PFSA; C4-C8), perfluoroalkyl carboxylic acid (PFCA; C6-C15) and FOSA. In the data evaluation, observations from other monitoring programmes and research campaigns are included (river, marine surface water, sediment, and top predators) to set the observations from the Swedish Monitoring Program for Contaminants in Marine Biota into context. After an initial exponential increase in PFAS concentrations, we found that PFAS displayed a rapid response to phase-out and regulations in the early 2000s. As a result, PFAS concentrations stabilized (rather than displaying an immediate decrease). This is linked to the few removal pathways of the long lived PFAS homologues in the Baltic Sea water column. However, within the last decade PFAS has started to show significant declines at many stations, the exception being a few PFAS homologues (PFOA (C8) and PFNA (C9)). Two distinct water masses are present in the Greater Baltic Sea, North Sea water and Baltic Sea ...
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