Spatial and seasonal changes in levels of perfluoroalkyl acids (PFAAs) in surface water and sediment from a typical paper-making area in Vietnam

Perfluoroalkyl acids (PFAAs) have been increasingly reported in the aquatic environment but integrated evidence linking their occurrence in surface water and sediment in potential source areas for paper-making activities remains limited. This study reported the levels, spatial and seasonal changes of selected PFAAs in surface water (n = 40) and sediment (n = 25) from Phong Khe, the largest paper-recycling area in Vietnam. PFAA compounds with carbon number ≤ 8, which showed the highest detection frequencies in both seasons, also exhibited the highest concentrations in surface water. Concentrations of PFOS in more than 70% of surface water samples exceeded the environmental quality standard of the European Union. Total PFAA concentrations measured in sediments in Phong Khe during the dry season ranged from 0.03 to 6.32 ng/g, with a mean of 1.73 ng/g and a median of 0.88 ng/g. The results showed a spatially consistent change in levels of PFAAs with increasing distance from the discharge sources, following the order: drainage channels > Ngu Huyen Khe River > Cau River. In contrast to surface water, sediment samples exhibited higher detection frequencies and greater relative contributions from long-chain PFAAs than from short-chain homologues. Although ecological risks were generally within acceptable thresholds, some sensitive species, such as Chironomus plumosus , still showed low to moderate risk. Source apportionment using PCA suggested seasonal differences in the sources and controlling factors of PFAAs in surface water.