title: Experimental Solubility Approach to Determine PDMS-Water Partition Constants and PDMS Activity Coefficients.
abstract: Freely dissolved aqueous concentration and chemical activity are important determinants of contaminant transport, fate, and toxic potential. Both parameters are commonly quantified using Solid Phase Micro-Extraction (SPME) based on a sorptive polymer such as polydimethylsiloxane (PDMS). This method requires the PDMS-water partition constants, KPDMSw, or activity coefficient to be known. For superhydrophobic contaminants (log KOW >6), application of existing methods to measure these parameters is challenging, and independent measures to validate KPDMSw values would be beneficial. We developed a simple, rapid method to directly measure PDMS solubilities of solid contaminants, SPDMS(S), which together with literature thermodynamic properties was then used to estimate KPDMSw and activity coefficients in PDMS. PDMS solubility for the test compounds (log KOW 7.2-8.3) ranged over 3 orders of magnitude (4.1-5700 μM), and was dependent on compound class. For polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins (PCDDs), solubility-derived KPDMSw increased linearly with hydrophobicity, consistent with trends previously reported for less chlorinated congeners. In contrast, subcooled liquid PDMS solubilities, SPDMS(L), were approximately constant within a compound class. SPDMS(S) and KPDMSw can therefore be predicted for a compound class with reasonable robustness based solely on the class-specific SPDMS(L) and a particular congener's entropy of fusion, melting point, and aqueous solubility.
authors.affiliation: The University of Queensland , National Research Centre for Environmental Toxicology (Entox), 39 Kessels Road, Coopers Plains, QLD 4108, Australia.
authors.forename: Sharon
authors.initials: S
authors.lastname: Grant
authors.affiliation: The University of Queensland , National Research Centre for Environmental Toxicology (Entox), 39 Kessels Road, Coopers Plains, QLD 4108, Australia.
authors.forename: Veronika J
authors.initials: VJ
authors.lastname: Schacht
authors.affiliation: The University of Queensland , National Research Centre for Environmental Toxicology (Entox), 39 Kessels Road, Coopers Plains, QLD 4108, Australia.|UFZ - Helmholtz Centre for Environmental Research , Cell Toxicology, Permoserstraβe 15, 04318 Leipzig, Germany.|Eberhard Karls University , Environmental Toxicology, Center for Applied Geosciences, Hölderlinstraβe 12, 72074 Tübingen, Germany.
authors.forename: Beate I
authors.initials: BI
authors.lastname: Escher
authors.affiliation: Griffith University , School of Environment, 170 Kessels Road, Nathan, QLD 4111, Australia.
authors.forename: Darryl W
authors.initials: DW
authors.lastname: Hawker
authors.affiliation: The University of Queensland , National Research Centre for Environmental Toxicology (Entox), 39 Kessels Road, Coopers Plains, QLD 4108, Australia.
authors.forename: Caroline
authors.initials: C
authors.lastname: Gaus
mesh_terms: D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D011078:Polychlorinated Biphenyls / Q000737:chemistry; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives / Q000737:chemistry; D052617:Solid Phase Microextraction / Q000295:instrumentation / Q000379:methods*; D012995:Solubility; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D004129:Dimethylpolysiloxanes; D000072317:Polychlorinated Dibenzodioxins; D014874:Water Pollutants, Chemical; D014867:Water; C013830:baysilon; D011078:Polychlorinated Biphenyls