Concentrations of per- and polyfluoroalkyl substances in estuarine systems can vary greatly within tidal cycles

Per and poly-fluoroalkyl substances are currently of concern due to their widespread occurrence, resistance to degradation and potential toxicity. Major efforts are underway worldwide to assess environmental concentrations of PFAS, but most monitoring is done at a single time point. Little consideration is given to how such concentrations might vary over time. In this study, the concentrations of 44 PFAS were measured hourly over 24 h (two tidal cycles) in three estuaries in Victoria, Australia. The most prevalent compound was PFHxS at a maximum concentration of 72.3 ng/L. Concentrations of ΣPFAS showed between four- and seven-fold differences during the 24-hour sampling period. Environmental measurements showed this was likely due to seawater diluting the concentration of PFAS in the estuary during tidal influxes. Randomly timed grab samples thus have a high risk of mischaracterising the true range of concentrations of PFAS in estuarine systems and/or underestimating the highest concentration present, which may result in an underestimation of risk to such systems.