Dispersion and stratification of Per-and polyfluoroalkyl substances (PFAS) in surface and deep-water profiles: A case study of the Biscayne Bay area

Abstract

Per-and polyfluoroalkyl substances (PFAS) are a group of synthetic chemical compounds known for their persistent, bioaccumulation and toxic characteristics in all environmental compartments. As industrial and domestic applications of PFAS increase, their discharge into water bodies becomes of human and ecological concerns. Our research focuses on providing better understanding on the occurrence, vertical distribution, and dispersion of PFAS in surface and bottom water from inshore and offshore area of Biscayne Bay, Miami, Florida. We screened a total of 30 PFAS from inshore (N = 38) and offshore (N = 48) water samples using a semi-automated solid phase extraction (SPE) followed by instrumental analysis using Liquid chromatography-mass spectrometry techniques (LC-MS/MS). Our findings show a general surface-enrichment and depth-depletion pattern from inshore to offshore area. Average ∑PFAS loadings inshore (surface vs bottom; 29.52 ± 15.26 ng/L vs 21.45 ± 7.85 ng/L) is significantly greater than offshore (surface vs bottom; 5.18 ± 2.68 ng/L vs 2.42 ± 2.11 ng/L). PFOS had the highest mean concentration both inshore (6.36 ± 4.23 ng/L) and offshore (0.83 ± 0.87 ng/L). The most frequently detected (D·F > 91 %) PFAS are Perfluorooctane sulfonic acid (PFOS), Perfluorooctanoic acid (PFOA), Perfluoroheptanoic acid (PFHpA), Perfluorohexanoic acid (PFHxA), Perfluorobutanoic acid (PFBA), Perfluorobutane sulfonic acid (PFBS) and Perfluorohexane sulfonic acid (PFHxS) in surface water samples. PFOS/PFOA >1 suggests that point sources are the major contribution to PFAS burden in the Biscayne Bay. An innovative Inverse distance weighted interpolation (IDW) special modelling approach was implemented to predict the potential contribution of oceanic current on the dispersion of ∑PFAS loadings in surface and bottom profiles from canals (inshore) to offshore areas. This will provide insights into transport mechanisms of PFAS from source emissions, and risk assessments of potential impacts on human and aquatic life in the Bay.