Tributary Loading and Sediment Desorption as Sources of PFAS to Receiving Waters

Transport of per- and polyfluoroalkyl substances (PFAS) to the Great Lakes is of great importance as this large freshwater system provides drinking water to over 40 million people. Tributary PFAS loading to the Great Lakes is poorly characterized, and the role of sediments as a source or sink of PFAS is largely unknown. We quantified 10 perfluoroalkyl acids (PFAAs) in water (4–1310 ng/L) and sediment (below detection to 3255 ng/kg) of 41 tributaries to Green Bay of Lake Michigan. We demonstrate that tributary discharge plays a major role in PFAS contribution to receiving waters. In this system, three large rivers (i.e., Fox, Menominee, and Peshtigo Rivers) contribute two-thirds of the total tributary PFAA loading to Green Bay despite their relatively low concentrations. This circumvents the current regulatory focus on sites with high concentrations. Tributary PFAA composition is linked to likely sources, including a fire-fighting foam manufacturer, other industrial activities, and airports. In addition to tributary discharge, we show that tributary sediments can contribute to PFAA transport via desorption. Perfluorooctanesulfonate rapidly desorbs from contaminated riverbed sediments when equilibrated with Lake Michigan water, indicating that sediments may act as a PFAS source if water concentrations are reduced by pollution mitigation methods.