Perfluorinated alkyl acids in surface and deep water from the Western Indian Ocean: A comparison with global data

This paper offers a comparative analysis of perfluoroalkyl substances (PFAS) in oceans and freshwater systems. Included are surface water and deep-water samples to provide a snapshot of the occurrence of these substances in a global context. Emphasis is given to the Western Indian Ocean (WIO), which has unique features due to a large land mass at low latitudes. In addition, the WIO is warmer than many other aquatic systems and is characterized by high salinity. The presence of PFAS and its distribution around the globe identified certain activities, like the use of fire-fighting foams in fire training at international airports as a source of contamination even in remote areas such as the Pacific Islands. In Brazil, the industrial area around São Paulo clearly showed much higher contamination with PFAS than the Amazon delta. In the WIO samples, consisting of vertical and horizontal transects, perfluorooctanoic acid (PFOA) was more abundant than perfluorosulfonic acid (PFOS) and also had higher concentrations. Overall, PFAS concentrations were much lower in the WIO samples as the majority of samples were below detection limits for PFOS and PFOA. The vast difference in the southern hemisphere marine waters is due to high PFAS concentrations found elsewhere, such as off the coast of South America, contrasting with the low concentrations in the Indian Ocean. This may be due to the South Equatorial Current that traverses thousands of kilometers of ocean with no substantial local inputs but is subject to losses of PFAS to the atmosphere and dilution due to mixing. On the east coast of Africa, only two samples were indicating continental contributions from rivers. The complex oceanic circulation of the Indian Ocean complicates the interpretation of PFAS source and fate, suggesting that patterns elsewhere in the world may not be directly applicable to the WIO.