Occurrence and fate of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in an urban aquifer located at the Besòs River Delta (Spain)

Due to the increasing demand of water, urban aquifers are an alternative source of water supply. However, they are at risk of contamination from persistent and mobile organic compounds (PMOCs), especially per- and polyfluoroalkyl substances (PFASs), which are artificial organic substances widely used across various industrial sectors. PFASs are considered toxic, mobile and persistent, and have therefore gained significant attention in environmental chemistry. Moreover, PFASs precursors transform into more recalcitrant and mobile products under natural conditions. Therefore, it is needed to investigate the fate of PFASs when they reach aquifers to use groundwater safely. However, there is limited information about the processes which affect their behaviour in groundwater, especially at the field-scale. In this context, the aim of this investigation is to assess and identify processes that control the evolution of PFASs in an urban aquifer in Barcelona, where groundwater behaves analogously to a river bank filtration system. A part from PFASs, 4 PMOCs were also analysed. During a summer campaign, 21 groundwater and 6 river samples were collected revealing the presence of 17 PFASs products, 3 novel PFASs and 4 PMOCs non-PFASs. PFASs products were found to be ubiquitous, with the highest concentrations found in PFBS, TFA and TFSA. Non-PFASs and novel PFASs, with the exception of Sulfanilic acid, were found to be present in very low concentrations. It was observed that the redox conditions influence the behaviour of a number of PFASs controlling their attenuation capacity or recalcitrant behaviour. Most substances showed accumulation, possibly explained by sorption/desorption processes or by transformation processes, highlighting the challenges associated with PFASs remediation. In addition, the PFAS TFSA and two of the longest chain PFASs detected presented removals at different intensities. Our results will have tremendous implications for establishing the evolution of PFASs along the groundwater flow and might be extended to similar research areas such as Manage Aquifer Recharge techniques.