The Distribution and Seasonality of Per- and Polyfluoroalkyl Substances (PFAS) in the Vertical Water Column of a Stratified Eutrophic Freshwater Lake

The vertical distribution and potential variability of Per- and Polyfluoroalkyl substances (PFAS) in the water column of lacustrine systems is important to know for sampling and monitoring purposes, but could also relate to details of their fate, transport, and distribution. In this study, the water column of a eutrophic freshwater lake (Lake Monona, Madison, WI, USA) was sampled vertically for PFAS during summer stratification at several depths (surface microlayer to 1 m from the bottom) and then monitored at four dates and three depths the following year to assess seasonality. PFAS concentration did not exhibit vertical stratification or large variability in the water column. However, seasonal variation in PFAS concentration was detected, as well as an increase in PFAS concentration related to drought conditions. This study suggests that a surface water grab sample may be a sufficient representative of the water column for the basic monitoring of PFAS. But a single sample during the year may not provide a complete understanding of the lake, and multiple samples should be taken to capture and understand important seasonal events.