Dam operation altered profiles of per- and polyfluoroalkyl substances in reservoir.

Information on the impact of dam operation on per- and polyfluoroalkyl substances (PFASs) distribution in reservoirs is very limited. In the present study, water, riparian soils and floating wastes samples were collected from the Three Gorges Reservoir, China during the storage and the discharge periods to characterize the PFASs distribution. The total PFASs concentrations of water samples in the storage period (50.4-146 ng/L) were 4.7 times higher than those in the discharge period (1.40-38.6 ng/L). The main types of PFASs in water samples changed from PFOA in the discharge period to short-chain species in the storage period. The main analogues in riparian soils and floating wastes were PFOA and PFOS. Wastes contributed little to PFASs mass in the reservoir, while PFASs accumulated in soils accounted for 49.7 % of the total mass when the riparian zone was submerged during the storage period. Changes in profiles of PFASs caused by dam operation suggested that the potential water safety and the shift of riparian soils between source and sink of PFASs may vary with the annual operation cycle of dam. The water resources protection in reservoirs needs strategies that consider the variation of dam operation cycle.