Spatial distribution of per- and polyfluoroalkyl substances (PFAS) in natural and restored intertidal wetlands in the Scheldt estuary

Due to high human activity in coastal ecosystems, tidal marshes have become one of the most threatened natural ecosystems on the planet, with a significant decline in their ecosystem services as a result. The tidal marshes, flats and channel networks of estuaries each have their own distinct hydrodynamics, sedimentology and ecology which may affect the environmental fate and behaviour of pollutants. Intertidal areas may retain pollutants, hence impacting organisms that live, forage, or breed in these areas. Therefore, we investigated the spatial distribution of PFAS in sediments of intertidal areas in the Scheldt estuary (N Belgium & SW Netherlands), and to what extent this varies between different eco-geomorphic zones and between an old natural intertidal site (drowned land of Saeftinghe) and recently restored intertidal site (Hedwige-Prosperpolder; HPP), where tides were re-introduced. Furthermore, we investigated whether this distribution is affected by sediment characteristics and distance from the estuarine main channel. Associations between PFAS levels in sediments from the marshes and plants were investigated. Finally, we compared PFAS levels prior and after re-introduction of tides in the restoration site. Our results show signs of both historical and recent PFAS emissions, and suggest that the geomorphology of intertidal areas could play a role in the spatial distribution of PFAS in sediments. In general, the vegetation and the higher intertidal elevation in the marshes slow down currents, causing more deposition of finer sediment and higher PFAS concentrations. Distance from the estuarine main channel, grain size and organic matter content were less determining factors in the environmental fate. The re-introduction of tidal flooding in HPP leads to an enrichment with PFAS. Three PFAS were detected prior to tidal re-introduction, whereas eight PFAS were detected after. Concentrations of PFOS, PFOA and PFBS were respectively 12x, 3x and 5x higher after re-introduction. Although environmental risks in the intertidal areas were not assessed in this study, the enrichment could be beneficial for the Scheldt estuary and North Sea, as PFAS are filtered from the estuary and ecological risks in the estuary and adjacent sea are likely reduced. Moreover, removal of contaminated sediment beds and plants from intertidal areas would allow for remediation of the ecosystem, something which is more difficult when the pollution stays in the estuarine channel or sea.

Abstract of an Oral Presentation or a Poster

SETAC Europe 35th annual meeting, 11-15 May 2025, Vienna, Austria