Spatial distribution, vertical profiles and transport of legacy and emerging per- and polyfluoroalkyl substances in the Indian Ocean.

The contamination status and transport of per- and polyfluoroalkyl substances (PFASs) in the seawater of the Indian Ocean (IO) and an adjacent subregion of the Northwest Pacific Ocean (NWPO) were investigated. Eight legacy PFASs were widely distributed in the surface seawater, and perfluoroheptanoic acid (PFHpA) and perfluorooctanoic acid (PFOA) were the two predominant PFASs. ΣPFAS concentration decreased in the following order: NWPO>Joining area of Asia and Indian-Pacific Oceans (JAIPO)>Northeast Indian Ocean>Southwest Indian Ocean. Hexafluoropropylene oxide-dimer acid, a replacement surfactant for PFOA was extensively detected in the IO (~34.8 pg/L) for the first time, showing an early sign of emerging PFAS spread in global open oceans. Eight depth profiles across the JAIPO (down to 5433 m depth) revealed a "surface-enrichment" and "depth-depletion" pattern for PFASs in the water column, and two noticeable fluctuations were mainly located at depths of 150–200 and 200–500 m. Physical processes, including eddy diffusion, and the origin and trajectory of water mass were crucial factors for structuring PFAS vertical profiles. Mass transport estimates revealed a remarkable PFOA contribution through the JAIPO to IO carried by the Indonesian Throughflow, and a nonnegligible PFHpA contribution from Antarctic Immediate Water to deep water of the JAIPO driven by thermohaline circulation. [Display omitted] This study clarified that legacy and emerging PFASs in the different open areas of the Indian Ocean (IO), contributing to the understanding of the contamination status, transport, and interbasin exchange of PFASs in global open oceans. HFPO-DA was extensively detected in the IO, showing an early sign of emerging PFASs spread in global open oceans. Our results demonstrated the effect of physical processes, including oceanic circulation, eddy diffusion, and origin and trajectory of water mass, on the structuring of large-scale transport and fate of PFASs and found the remarkable contribution of PFASs from the Pacific Ocean to the IO. • The total PFASs concentration decreased in an order of NWPO>JAIPO>NWIO>SWIO. • PFOA and PFHpA contamination in the Indian Ocean are more prominent than PFOS. • HFPO-DA are detected extensively for the first time in the Indian Ocean. • PFASs vertical profiles show a "surface-enrichment and depth-depletion" pattern. • A remarkable PFOA contribution from the JAIPO to the Indian Ocean is demonstrated. [ABSTRACT FROM AUTHOR]