title: Organic Carbon/Water and Dissolved Organic Carbon/Water Partitioning of Cyclic Volatile Methylsiloxanes: Measurements and Polyparameter Linear Free Energy Relationships.
abstract: The sorption of cyclic volatile methyl siloxanes (cVMS) to organic matter has a strong influence on their fate in the aquatic environment. We report new measurements of the partition ratios between freshwater sediment organic carbon and water (KOC) and between Aldrich humic acid dissolved organic carbon and water (KDOC) for three cVMS, and for three polychlorinated biphenyls (PCBs) that were used as reference chemicals. Our measurements were made using a purge-and-trap method that employs benchmark chemicals to calibrate mass transfer at the air/water interface in a fugacity-based multimedia model. The measured log KOC of octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) were 5.06, 6.12, and 7.07, and log KDOC were 5.05, 6.13, and 6.79. To our knowledge, our measurements for KOC of D6 and KDOC of D4 and D6 are the first reported. Polyparameter linear free energy relationships (PP-LFERs) derived from training sets of empirical data that did not include cVMS generally did not predict our measured partition ratios of cVMS accurately (root-mean-squared-error (RMSE) for logKOC 0.76 and for logKDOC 0.73). We constructed new PP-LFERs that accurately describe partition ratios for the cVMS as well as for other chemicals by including our new measurements in the existing training sets (logKOC RMSEcVMS: 0.09, logKDOC RMSEcVMS: 0.12). The PP-LFERs we have developed here should be further evaluated and perhaps recalibrated when experimental data for other siloxanes become available.
authors.affiliation: Department of Environmental Science and Analytical Chemistry, ACES, Stockholm University , Svante Arrhenius väg 8, SE-114 18 Stockholm, Sweden.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Abrahamsson
authors.affiliation: Department of Environmental Science and Analytical Chemistry, ACES, Stockholm University , Svante Arrhenius väg 8, SE-114 18 Stockholm, Sweden.|Department of Cell Toxicology, Helmholtz Centre for Environmental Research, UFZ , Permoserstraße 15, DE-04318 Leipzig, Germany.
authors.forename: Annika
authors.initials: A
authors.lastname: Jahnke
authors.affiliation: Department of Environmental Science and Analytical Chemistry, ACES, Stockholm University , Svante Arrhenius väg 8, SE-114 18 Stockholm, Sweden.
authors.forename: Amelie
authors.initials: A
authors.lastname: Kierkegaard
authors.affiliation: Department of Environmental Science and Analytical Chemistry, ACES, Stockholm University , Svante Arrhenius väg 8, SE-114 18 Stockholm, Sweden.
authors.forename: Matthew
authors.initials: M
authors.lastname: MacLeod
mesh_terms: D002244:Carbon / Q000032:analysis*; D018499:Linear Energy Transfer; D008962:Models, Theoretical; D012833:Siloxanes / Q000032:analysis*; D012997:Solvents / Q000737:chemistry; D014867:Water / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D012833:Siloxanes; D012997:Solvents; D014874:Water Pollutants, Chemical; D014867:Water; C114768:decamethylcyclopentasiloxane; D002244:Carbon; C024064:octamethylcyclotetrasiloxane; C542115:dodecamethylcyclohexasiloxane