The distribution of per- and poly-fluoroalkyl substances in the global marine water

Abstract

Per- and poly-fluoroalkyl substances (PFASs) are a family of artificial organic compounds with at least one hydrogen atom along the carbon backbone substituted with fluorine. They are widely used as surfactants and additives in industries including electroplating, firefighting, coating, textile and so forth because they are chemically and thermally inert and both hydrophobic and oleophobic. PFASs are ubiquitous in various environmental matrix and have caused great concerns on their global transport and adverse impacts on environment. Hence, perfluorooctane sulfonate acid (PFOS) and related substances were listed under Annex B of the Stockholm Convention in 2009. In the recent two decades, an increasingly variety of PFASs are found in the environment (e.g., shorter-chain PFAAs, fluorotelomers, perfluoropolyethers, perfluoroalkyl phosphonic acids, perfluoroalkyl phosphinic acids, polyfluoroalkyl phosphate esters, chlorine or hydro substituted polyfluoroalkyl substances, etc.). They occur not only in inland areas but also in oceans and seas, even in remote areas such as polar areas. This prompts the necessity to figure out the fate of PFASs all over the world. Regarded as one of the crucial sinks of pollutants, oceans and seas play a pivotal role in PFASs transport in the environment. Researches on the marine pollution of PFASs are increasing in the recently years. In this paper, we summarized the recent researches on the spacial and temporal trends of legacy and emerging PFASs in the Atlantic Ocean, the Pacific Ocean, the Indian Ocean, the Arctic Ocean and the Southern Ocean from 2002 to 2016, respectively. We also summarized the researches on the occurrence of PFASs in water at different depths in the middle of the Atlantic Ocean, in the south and northwest of the Pacific Ocean, in the Southern Ocean and in the Arctic Ocean, respectively. The results indicate that a variety of emerging PFASs as substitutes of legacy PFASs are being detected in the oceans, and they are transported from offshore areas to remote areas via currents. The concentrations of PFASs in the seawater decrease gradually with the distance from the coast increasing. The PFASs in the surface seawater of the Arctic Ocean are mainly derived from the North Atlantic Ocean via currents and the degradation of PFASs precursors via atmospheric transport. The occurrence of PFASs in the deep seawater implies that the global thermocline and/or halocline circulation influences the three dimensional transport of PFASs in the oceans and seas. The PFASs transport globally via the following pathways: (1) long-range atmospheric transport (LRAT) plus degradation and precipitation for neutral PFASs precursors; (2) currents and thermocline and/or halocline circulation for ionic PFASs; (3) marine aerosols for perfluorooctanoate; (4) food chain and migratory biota acting as biovectors. In future, more attention should be paid on PFASs in the Indian Ocean and the Southern Ocean, where these is a large data gap on the occurrence of PFASs, which hampers understanding of global transport of PFASs via seas and oceans. Further researches are warranted on the emerging PFAS pollutants in seawater in seas and oceans giving that they are increasingly produced and applied globally.