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Environ Sci Technol

Title:		Sorption-induced effects of humic substances on mass transfer of organic pollutants through aqueous diffusion boundary layers: the example of water/air exchange
Author(s):		Ramus K; Kopinke FD; Georgi A;
Address:		"Department of Environmental Engineering, Helmholtz Centre for Environmental Research - UFZ, Permoserstr. 15, D-04318 Leipzig, Germany"
Journal Title:		Environ Sci Technol
Year:		2012
Volume:		20120203
Issue:		4
Page Number:		2196 - 2203
DOI:		10.1021/es2038382
ISSN/ISBN:		1520-5851 (Electronic) 0013-936X (Linking)
Abstract:		"This study examines the effect of dissolved humic substances (DHS) on the rate of water-gas exchange of organic compounds under conditions where diffusion through the aqueous boundary layer is rate-determining. A synthetic surfactant was applied for comparison. Mass-transfer coefficients were determined from the rate of depletion of the model compounds by means of an apparatus containing a stirred aqueous solution with continuous purging of the headspace above the solution. In addition, experiments with continuous passive dosing of analytes into the water phase were conducted to simulate a system where thermodynamic activity of the chemical in the aqueous phase is identical in the presence and absence of DHS. The experimental results show that DHS and surfactants can affect water-gas exchange rates by the superposition of two mechanisms: (1) hydrodynamic effects due to surface film formation ('surface smoothing'), and (2) sorption-induced effects. Whether sorption accelerates or retards mass transfer depends on its effect on the thermodynamic activity of the pollutant in the aqueous phase. Mass transfer will be retarded if the activity (or freely dissolved concentration) of the pollutant is decreased due to sorption. If it remains unchanged (e.g., due to fast equilibration with a sediment acting as a large source phase), then DHS and surfactant micelles can act as an additional shuttle for the pollutants, enhancing the flux through the boundary layer"
Keywords:		Adsorption Benzene/chemistry Benzopyrans/*chemistry Diffusion *Humic Substances Octanes/chemistry Volatilization Water Pollutants/*chemistry;
Notes:		"MedlineRamus, Ksenia Kopinke, Frank-Dieter Georgi, Anett eng Research Support, Non-U.S. Gov't 2012/01/25 Environ Sci Technol. 2012 Feb 21; 46(4):2196-203. doi: 10.1021/es2038382. Epub 2012 Feb 3"