Seamounts create local hotspots of per- and polyfluoroalkyl substances in the oligotrophic open ocean

As one persistent organic pollutant, per- and polyfluoroalkyl substances (PFAS) are widely present in oceans. Seamounts, widely distributed in the global deep sea, are hotspots for marine biodiversity and a wide range of fishery resources, can dramatically alter ocean currents direction and then regulate the distribution of pollutants. However, their impact on PFAS distribution is still unknown. This study conducted the first comprehensive depth-profile investigation of PFAS distribution in the Caiwei, Weijia, and Fedorov seamounts along the Magellan Seamount Chain in the Northwestern Pacific. Here, we report 15 targeted PFAS in seawater of the deep-sea seamount. The main findings of the study are as follows: (1) the average depth-integrated concentration of PFAS in the water column shallower than 1000 m at seamount summits were 112.0 ± 78.4 pg/L, which were 1.4 times higher than those at the surrounding basin reference stations; (2) the mesopelagic zone of seamounts is a hotspot for PFAS distribution, characterized by obvious enrichment, highlighting a distinct “PFAS seamount effect”; (3) alternative PFAS account for a higher proportion than legacy PFAS and exists obvious enrichment in the mesopelagic zone, indicating that alternative PFAS are the dominated PFAS pollutants in this region. This study highlights the importance of enhanced baseline monitoring of pollutants, particularly alternative PFAS concentrations, in conservation efforts for seamount protection strategies.