Spatio-temporal dynamics of per and polyfluoroalkyl substances (PFASs) and transfer to periphytic biofilm in an urban river: case-study on the River Seine

This study addresses the spatio-temporal dynamics of per and polyfluoroalkyl substances (PFASs) in a highly urbanized freshwater hydrosystem, the Seine River (NW France). The distribution of PFASs between water, sediment, and periphytic biofilm was investigated at three sampling sites along a longitudinal gradient upstream and downstream from the Paris urban area. Seasonal variability was assessed through four sampling campaigns performed under contrasting hydrological conditions. In the dissolved phase, aPFASs fluctuated between 2 and 9 ng L-1 upstream and 6-105 ng L-1 downstream from Paris. Negative correlations between dissolved PFAS levels and river flow rate were generally observed, corroborating the predominance of point-source PFAS inputs at these sites. 18/19 target PFASs were detected, with a predominance of PFHxS and PFOS (20% of aPFASs each), except for the farthest downstream site where 6:2 FTSA was prevalent (35 +/- 8% of aPFASs), likely reflecting industrial and urban inputs. In biofilms, aPFASs fell in the 4-32 ng g(-1) dw range, and substantial bioconcentration factors (BCFs) were reported for PFNA, PFDA, and PFOS (log BCF 2.1-4.3), higher than those of PFHxS or PFOA. BCFs varied inversely with dissolved PFAS levels, potentially pointing to concentration-dependent bioaccumulation. Biofilm community characteristics (C/N ratio) may also be an influential determinant of PFAS bioaccumulation.