title: Reversible and irreversible sorption of perfluorinated compounds (PFCs) by sediments of an urban reservoir.
abstract: Uncertainty about the extent to which contaminant sorption by suspended solids and bed sediments is irreversible is a major impediment for modeling and managing the water quality of surface water resources. This study examined reversible and irreversible sorption of several perfluorinated compounds (PFCs) to bed sediments from an urban reservoir. PFCs investigated include C4, C6, C8, C9 and C10 perfluoroalkanoate homologues (PFBA, PFHxA, PFOA, PFNA and PFDA, respectively) and perfluorooctane and hexane sulfonate (PFOS and PFHxS, respectively). Although sorption branches of the PFOS, PFNA and PFDA isotherms were nearly linear (implying a partitioning-like process), desorption experiments indicated that a fraction of the sorbed PFCs were entrapped and resistant to desorption. The hysteretic desorption branches were approximately linear. Irreversibility increased with chain length and was nearly complete for PFDA (thermodynamic irreversibility index (TII) 0.98). For the weakly sorbing PFOA and PFHxS, sorption was largely reversible. Data suggest that (1) for the strongly sorbing PFCs, e.g. PFNA, PFDA and PFOS, bed sediments acted predominantly as irreversible sinks, (2) aqueous concentrations of the moderately sorbing PFCs (PFOA and PFHxS) are buffered by reversibly sorbing suspended solids, and (3) the short-chain PFCs (PFBA and PFHxA) are not significantly sorbed and therefore not expected to be significantly influenced by sediment transport. Situations in which highly contaminated particles entering relatively clean water bodies, equilibrium is approached from the reverse (desorption) direction. For irreversibly sorbed contaminants field-based K(D) values will be higher than the K(D) values derived from laboratory sorption data obtained from forward sorption experiments.
authors.affiliation: Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, E1A 07-03, Singapore 117576, Singapore.
authors.forename: Huiting
authors.initials: H
authors.lastname: Chen
authors.affiliation: Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, E1A 07-03, Singapore 117576, Singapore.
authors.forename: Martin
authors.initials: M
authors.lastname: Reinhard
authors.affiliation: Environment Building, 40 Scott Road, Public Utilities Board (PUB), Singapore.
authors.forename: Viet Tung
authors.initials: VT
authors.lastname: Nguyen
authors.affiliation: Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, E1A 07-03, Singapore 117576, Singapore; NUS Environmental Research Institute, National University of Singapore, 5A Engineering Drive 1, #02-01, Singapore 117411, Singapore. Electronic address: ceeginyh@nus.edu.sg.
authors.forename: Karina Yew-Hoong
authors.initials: KY
authors.lastname: Gin
mesh_terms: D000327:Adsorption; D002208:Caproates / Q000737:chemistry / Q000302:isolation & purification; D002210:Caprylates / Q000737:chemistry / Q000302:isolation & purification; D002851:Chromatography, High Pressure Liquid; D005466:Fluorocarbons / Q000737:chemistry / Q000302:isolation & purification*; D019015:Geologic Sediments / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008962:Models, Theoretical; D013499:Surface Properties; D014507:Urbanization; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000302:isolation & purification*; D060753:Water Quality
chemical_list: D002208:Caproates; D002210:Caprylates; D005466:Fluorocarbons; D014874:Water Pollutants, Chemical; C033094:perfluorobutyric acid; C023036:perfluorooctanoic acid; C479228:perfluorohexanoic acid
keywords: Desorption; Irreversible sorption; PFCs; Reversible sorption; Sediments