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Evaluating the salting-out effect on the organic carbon/water partition ratios (KOC and KDOC) of linear and cyclic volatile methylsiloxanes: Measurements and polyparameter linear free energy relationships
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
2016 (English)In: Journal of Chemical and Engineering Data, ISSN 0021-9568, E-ISSN 1520-5134, Vol. 61, no 9, 3098-3108 p.Article in journal (Refereed) Published
Abstract [en]

Dissolved inorganic salts influence the partitioning of organic chemicals between water and sorbents. We present new measurements of the salting-out constants (Ks) for partition ratios between water and organic carbon (KOC) and between water and dissolved organic carbon (KDOC) of three cyclic volatile methylsiloxanes (cVMS), two linear volatile methylsiloxanes (lVMS), three polychlorinated biphenyls (PCBs), and α-hexachlorocyclohexane (α-HCH). Ks, KOC, and KDOC were derived from volatilization rates of the chemicals from mixtures of water and organic carbon with varying concentrations of sodium chloride in a purge-and-trap system. KOC and KDOC values at different salinities were determined by fitting their values to reproduce observed volatilization rates using a fugacity-based multimedia model and assuming first-order kinetics for volatilization. The Ks values of cVMS and lVMS ranged from 0.16–0.76. The log KOC of cVMS and lVMS in fresh water interpolated from our measurements ranged from 5.20 to 7.36 and the log KDOC values from 5.04 to 6.72. Polyparameter linear free energy relationships (PP-LFERs) trained with data sets without measurements for siloxanes failed to accurately describe the log KOC and log KDOC of cVMS and lVMS. Including our measurements for cVMS and lVMS substantially improved the fit. PP-LFERs trained with data for Ks from solubility measurements do not describe our new measurements well regardless of whether or not they are included in the training set, which may reflect differences in the salting-out effect on partitioning to organic carbon versus on solubility.

Place, publisher, year, edition, pages
2016. Vol. 61, no 9, 3098-3108 p.
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-134536DOI: 10.1021/acs.jced.6b00196ISI: 000383005500021OAI: oai:DiVA.org:su-134536DiVA: diva2:1034009
Available from: 2016-10-10 Created: 2016-10-10 Last updated: 2017-11-29Bibliographically approved
In thesis
1. Partitioning and persistence of volatile methylsiloxanes in aquatic environments
Open this publication in new window or tab >>Partitioning and persistence of volatile methylsiloxanes in aquatic environments
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The presence of volatile methylsiloxanes (VMS) in the environment has raised concerns among environmental chemists and regulators about their persistence and the risks they may pose to the environment. This thesis explores the partitioning and persistence of VMS in aquatic environments. In Paper I, we reported new measurements of the organic carbon/water (KOC) and dissolved organic carbon/water (KDOC) partition ratios of three cyclic volatile methylsiloxanes (cVMS) and of three polychlorinated biphenyls (PCBs), which were used as reference chemicals. We combined new measurements with existing data to construct polyparameter linear free energy relationships (PP-LFER) that describe the KOC and KDOC of diverse sets of chemicals. The findings suggest that cVMS do not conform to single-parameter regressions that relate the chemicals’ KOC to their octanol/water partition ratio (KOW). PP-LFERs can accurately describe the KOC and KDOC of cVMS but only if cVMS are included in their training sets. In Paper II, we studied the effect of salinity on the KOC and KDOC of three cVMS, two linear volatile methylsiloxanes (lVMS) and three PCBs. We also evaluated the predictive power of the PP-LFERs constructed in Paper I by testing them on the newly measured KOC values of lVMS. The KOC and KDOC increased with increasing salinities similarly to those of the PCBs. PP-LFERs that were trained with datasets that included siloxanes could predict the KOC and KDOC of other siloxanes more accurately than PP-LFERs without siloxanes in the training set. In Paper III, we evaluated the effect of temperature on the KOC of VMS and we compared our measurements of the enthalpy of sorption to organic carbon (ΔHOC) to existing measurements of the enthalpy of phase change between octanol and water (ΔHOW). Due to the scarcity of ΔHOC data in the literature it is common practice in modeling calculations to use ΔHOW instead when correcting for temperature changes. The KOC of cVMS increased with decreasing temperatures. Moreover, our results indicate that ΔHOC and ΔHOW may be intrinsically different and hence replacing ΔHOC with ΔHOW in modeling calculations could lead to substantial errors, especially for VMS. In Paper IV, we explored the environmental fate of VMS in aquatic environments using multimedia models. In particular, we assessed the differences that may occur in calculations of persistence due to (i) the reported KOC measurements of VMS differing by one log unit (ii) the influence of salinity on KOC, and (iii) the differences in the reported ΔHOC and ΔHOW measurements of VMS. The calculated residence times for decamethylcyclopentasiloxane (D5) in a site-specific scenario for a Norwegian fjord receiving siloxanes in wastewater ranged from 200 to 1000 days, and demonstrated that the selection of KOC values can result in substantially different calculated persistence. Future partitioning measurements of VMS in the real environment and mass-balance modeling studies in aquatic environments combined with field measurements could help us to deepen our understanding about their persistence and to assess the risks VMS may pose to the environment.

Place, publisher, year, edition, pages
Stockholm: Department of Environmental Science and Analytical Chemistry, Stockholm University, 2016. 32 p.
Keyword
siloxanes, organic carbon, sediment, partitioning, persistence
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-134592 (URN)978-91-7649-495-0 (ISBN)
Public defence
2016-11-24, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Submitted.

Available from: 2016-11-01 Created: 2016-10-11 Last updated: 2016-10-26Bibliographically approved

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