Effect of salinity and sediment characteristics on the sorption and desorption of perfluorooctane sulfonate at sediment-water interface Chun You, Chengxia Jia, Gang Pan * State Key Lab of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences,18 Shuangqing Road, Beijing 100085, China Salinity is an important environmental parameter affecting the transport and fate of PFOS in aquatic environment. article info Article history: Received 27 September 2009 Received in revised form 21 December 2009 Accepted 11 January 2010 Keywords: Perfluorooctane sulfonate Sorption Desorption hysteresis Salinity Salting-out effect Ca-bridging effect abstract This study investigated the influence of solution salinity, pH and the sediment characteristics on the sorption and desorption of perfluorooctane sulfonate (PFOS). The results showed that the sorption of PFOS onto sediment increased by a factor of 3 as the CaCl 2 concentration increased from 0.005 to 0.5 mol L 1 at pH 7.0, and nearly 6 at pH 8.0. Desorption hysteresis occurred over all salinity. The thermodynamic index of irreversibility (TII) values increased with increasing concentration of CaCl 2 . Maximum irreversibility was found in the sorption systems with CaCl 2 in the concentration of 0.5 mol L 1 . The results suggested that PFOS can be largely removed from the water with increasing salinity, and get trapped onto sediments irreversibly. These phenomena could be explained by salting-out effect and Ca-bridging effect. Studies also suggested that the content of total organic carbon is the dominant psychochemical properties of sediment controlling the sorption of PFOS. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Recently, the environmental fate of PFOS has raised public and scientific concerns for its high bioaccumulation, extreme persis- tence, and toxic properties, such as endocrine-disrupting activity and carcinogenesis (Beach et al., 2006). Many studies have shown that PFOS is ubiquitously detected in the environment, even in remote arctic areas (Giesy and Kannan, 2001; Report RIKZ/ 2002.043, 2002). Because of the low volatility and high solubility of PFOS, the transport of PFOS in the aquatic environment is considered an important process in controlling its distribution and fate. Sorption and desorption behaviors are important processes that control the distribution, transport and fate of chemicals in aquatic environment. Since PFOS contains both hydrophobic and hydro- philic functionalities, it is expected to behave differently from traditional hydrophobic pollutants (Villagrasa et al., 2006). Signif- icant sorption of PFOS onto sediment has been reported from laboratory and field data (Higgins and Luthy, 2006; Nakata et al., 2006), and sediment has been confirmed as one of the final sinks of perfluorocarboxylates (Prevendouros et al., 2006). Higgins and Luthy (2006) have reported that the total organic carbon (TOC) of sediment is the dominant parameter affecting the sorption, and that hydrophobic interaction is the underlying sorption mecha- nism. When organic carbon is not presented, such as sorption on sand, clay, and iron oxide, surface electrostatic interaction is considered as the main sorption mechanism for PFOS (Johnson et al., 2007). On the other hand, field data from Rivers in America and Japan show that the concentrations of PFOS in water are detectable, while the concentrations in sediment are below the quantification limit, which suggest that the distribution of PFOS into sediment due to sorption is negligible (Hansen et al., 2002; Senthilkumar et al., 2007). These results suggest that the sorption behavior of PFOS may vary greatly under different sorption conditions, which mean that besides the physiochemical characteristics of the sorbent, environmental parameters of aquatic system, such as salinity and pH, also affect the sorption of PFOS. For the ionic organic chemicals, such as PFOS, salinity and the solution pH not only influence the speciation of sorbate in solution, but also influence the properties of sorbent, such as surface charge and structure of sediment organic matter (SOM), which consequently affect the extent of sorption of hydrophilic organic pollutants (Liu et al., 2001). Martin et al. (2004) suggest that sediments are the major sources of perfluoroalkyl introduction into the food web in Lake Ontario. Consequently, this puts forward an important issue on the bioavailability of sediment-bound PFOS, whether sediments serve as long-term sources of PFOS to the biosphere. Understanding the * Corresponding author. Tel.: þ86 10 62849686; fax: þ86 10 62923541. E-mail address: gpan@rcees.ac.cn (G. Pan). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2010.01.009 Environmental Pollution 158 (2010) 1343–1347