title: Solubility enhancement of dioxins and PCBs by surfactant monomers and micelles quantified with polymer depletion techniques.
abstract: Partitioning of super-hydrophobic organic contaminants (SHOCs) to dissolved or colloidal materials such as surfactants can alter their behaviour by enhancing apparent aqueous solubility. Relevant partition constants are, however, challenging to quantify with reasonable accuracy. Partition constants to colloidal surfactants can be measured by introducing a polymer (PDMS) as third phase with known PDMS-water partition constant in combination with the mass balance approach. We quantified partition constants of PCBs and PCDDs (log KOW 5.8-8.3) between water and sodium dodecyl sulphate monomers (KMO) and micelles (KMI). A refined, recently introduced swelling-based polymer loading technique allowed highly precise (4.5-10% RSD) and fast (<24 h) loading of SHOCs into PDMS, and due to the miniaturisation of batch systems equilibrium was reached in <5 days for KMI and <3 weeks for KMO. SHOC losses to experimental surfaces were substantial (8-26%) in monomer solutions, but had a low impact on KMO (0.10-0.16 log units). Log KMO for PCDDs (4.0-5.2) were approximately 2.6 log units lower than respective log KMI, which ranged from 5.2 to 7.0 for PCDDs and 6.6-7.5 for PCBs. The linear relationship between log KMI and log KOW was consistent with more polar and moderately hydrophobic compounds. Apparent solubility increased with increasing hydrophobicity and was highest in micelle solutions. However, this solubility enhancement was also considerable in monomer solutions, up to 200 times for OCDD. Given the pervasive presence of surfactant monomers in typical field scenarios, these data suggest that low surfactant concentrations may be effective long-term facilitators for subsurface transport of SHOCs.
authors.affiliation: The University of Queensland, National Research Centre for Environmental Toxicology (Entox), 39 Kessels Road, Coopers Plains, QLD, 4108, Australia. Electronic address: v.schacht@uq.edu.au.
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.
authors.forename: Sharon C
authors.initials: SC
authors.lastname: Grant
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, Permoserstraβe 15, 04318, Leipzig, Germany; Eberhard Karls University Tübingen, Center for Applied Geosciences, Environmental Toxicology, 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. Electronic address: c.gaus@uq.edu.au.
authors.forename: Caroline
authors.initials: C
authors.lastname: Gaus
mesh_terms: D004129:Dimethylpolysiloxanes / Q000737:chemistry; D060587:Groundwater / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D008962:Models, Theoretical; D011078:Polychlorinated Biphenyls / Q000737:chemistry*; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D012995:Solubility; D013501:Surface-Active Agents / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D004129:Dimethylpolysiloxanes; D008823:Micelles; D000072317:Polychlorinated Dibenzodioxins; D011108:Polymers; D013501:Surface-Active Agents; D014874:Water Pollutants, Chemical; C013830:baysilon; D011078:Polychlorinated Biphenyls
keywords: Partition constants; Polychlorinated biphenyls; Polychlorinated dibenzo-p-dioxins; Silanization; Surfactant monomers and micelles; poly(dimethylsiloxane)