Effects of salinity and organic matter on the partitioning of perfluoroalkyl acid (PFAs) to clay particles

Abstract

The influence of salinity and organic matter on the distribution coefficient (K(d)) for perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in a brackish water-clay system was studied. The distribution coefficients (K(d)) for PFAs onto inorganic clay surfaces increased with salinity, providing evidence for electrostatic interaction for the sorption of PFAs, whereas the relationship between K(d) and organic carbon content (f(oc)) suggested that hydrophobic interaction is the primary driving force for the sorption of PFAs onto organic matter. The organic carbon normalized adsorption coefficient (K(oc)) of PFAs can be slightly overestimated due to the electrostatic interaction within uncoated inorganic surfaces. In addition, the dissolved organic matter released from coated clay particles seemed to solvate PFA molecules in solution, which contributed to a decrease in K(d). A positive relationship between K(d) and salinity was apparent, but an empirical relationship for the 'salting-out' effect was not evident. The K(d) values of PFAs are relatively small compared with those reported for persistent organic pollutants. Thus, sorption may not be a significant route of mass transfer of PFAs from water columns in estuarine environments. However, enhancement of sorption of PFAs to particulate matter at high salinity values could evoke potential risks to benthic organisms in estuarine areas.

Distribution of perfluorinated compounds in Lake Taihu (China): Impact to human health and water standards

“…4) and the distribution map of Kd and ƒoc in the lake (Fig. 1) suggested that the organic carbon content dominated the distribution of PFOS in the sediment, which was consistent with earlier reported works where hydrophobic interactions played a strong role in the adsorption of long chain PFCs in the sediments (Jeon et al, 2011;Pan et al, 2009). …”

Heavy metal pollution in the surface water of the Yangtze Estuary: A 5-year follow-up study

“…Because of salt intrusion, the north branch often had significantly higher salinity and suspended sediment concentrations than the south branch (Zhang et al, 2011). As previously discussed, the increase of Cr and Cd along the north branch should be ascribed to the release of the particle-bound phase into the water phase under the drive of the ''salt-out effect'' (Jeon et al, 2011).…”

Partitioning of perfluorooctanesulfonate and perfluorohexanesulfonate in the aquatic environment after an accidental release of aqueous film forming foam at Schiphol Amsterdam Airport

“…where K D (L/kg) is the sediment-water distribution coefficient, C sediment is the concentration in sediment (mg/kg dry wt), and C water is the concentration in water (mg/L [6]. This difference may be caused by the difference in sediment composition and overall environmental parameters such pH and Ca 2þ , which are known to affect sorption of PFOS to sediment [10,15,[19][20][21][22][23]. Distribution coefficients were normalized to carbon content, using [6]; and higher than the 2.57 AE 0.13 from the laboratory experiment from Higgins and Luthy [15].…”