Modelling the transport of shipborne per- and polyfluoroalkyl substances (PFAS) in the coastal environment

Per- and polyfluoroalkyl substances (PFAS) are presently essential ingredients in aqueous film forming foam (AFFF) used for fire-fighting, but are also pervasive environmental contaminants. The use and subsequent release and transport of AFFF in the ocean environment from marine vessels has not been studied to date. A numerical model (Delft3D) was rigorously calibrated and validated for the hydrodynamics, and used to predict the transport of PFAS released instantaneously into a large harbour (Halifax Harbour, Nova Scotia) that is representative of coastal environments in eastern Canada and other parts of the world. The numerical model results indicate that PFAS released in the presence of strong winds and waves during a storm will travel up to 31 km in 2 days, approximately 40% farther than PFAS release during a time period dominated by tidal currents with light winds and small waves (<1 m). After a 10 day simulation, PFAS levels from release sites in the Inner Harbour were higher (40-60 μg/L) compared to PFAS levels from the Outer Harbour release site which had decreased to low levels (<1 μg/L) during a non-storm period. Along shorelines within the Harbour, PFAS concentrations remained elevated after 12 h (40-500 μg/L) and 48 h (2-300 μg/L). These concentrations are within the range of PFAS guidance values for recreational water use. The methods described here are relevant to studies of PFAS dispersion and transport in other coastal areas, and could be used to determine best practices for applications of AFFF in the coastal environment.