Horizontal and Vertical Distribution of Perfluoroalkyl Acids (PFAAs) in the Water Column of the Atlantic Ocean

Perfluoroalkyl acids (PFAAs) are widely distributed in the oceans which are their largest global reservoir, but knowledge is limited about their vertical distribution and fate. This study measured the concentrations of PFAAs (perfluoroalkyl carboxylic acids (PFCAs) with 6 to 11 carbons and perfluoroalkanesulfonic acids (PFSAs) with 6 and 8 carbons) in the surface and deep ocean. Seawater depth profiles from the surface to a 5000 m depth at 28 sampling stations were collected in the Atlantic Ocean from similar to 50 degrees N to similar to 50 degrees S. The results demonstrated PFAA input from the Mediterranean Sea and the English Channel. Elevated PFAA concentrations were observed at the eastern edge of the Northern Atlantic Subtropical Gyre, suggesting that persistent contaminants may accumulate in ocean gyres. The median sigma PFAA surface concentration in the Northern Hemisphere (n = 17) was 105 pg L-1, while for the Southern Hemisphere (n = 11) it was 28 pg L-1. Generally, PFAA concentrations decreased with increasing distance to the coast and increasing depth. The C6-C9 PFCAs and C6 and C8 PFSAs dominated in surface waters, while longer-chain PFAAs (C10-C11 PFCAs) peaked at intermediate depths (500-1500 m). This profile may be explained by stronger sedimentation of longer-chain PFAAs, as they sorb more strongly to particulate organic matter.Funding Agencies|UK Natural Environment Research Council through its National Capability Long-term Single Centre Science Programme, Climate Linked Atlantic Sector Science [NE/R015953/1]; Swedish Research Council [2016-04131]; FORMAS [2016-00644, 2020-01978]