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Environ Toxicol Chem

Title:		Determination of soil-water sorption coefficients of volatile methylsiloxanes
Author(s):		Kozerski GE; Xu S; Miller J; Durham J;
Address:		"Health and Environmental Sciences, Dow Corning, Auburn, Michigan, USA"
Journal Title:		Environ Toxicol Chem
Year:		2014
Volume:		20140804
Issue:		9
Page Number:		1937 - 1945
DOI:		10.1002/etc.2640
ISSN/ISBN:		1552-8618 (Electronic) 0730-7268 (Print) 0730-7268 (Linking)
Abstract:		"The sorption behaviors of 4 cyclic and linear volatile methyl siloxane (VMS) compounds between water and organic matter in 3 United Kingdom soils were studied by a batch equilibrium method using(13)C-enriched sorbates. Sorption and desorption kinetics and isotherms were determined for octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), octamethyltrisiloxane (L3), and decamethyltetrasiloxane (L4). Concentrations of [(13)C]-VMS in the soil and aqueous phases were measured directly by extraction and gas chromatography-mass spectrometry techniques. All VMS compounds were sorbed rapidly, reaching constant distributions in all soils by 24 h. Desorption kinetics were very rapid, with reattainment of equilibrium within 1 h. In the main, linear isotherms were observed for aqueous concentrations at or below 4% of the solubility limits. The average sorption organic carbon partition coefficient (logK(OC)) values across soils were 4.23 for D4, 5.17 for D5, 4.32 for L3, and 5.13 for L4, with standard deviations of 0.09 to 0.34. Desorption K(OC) values were systematically greater by 0.1 log units to 0.3 log units. The linear isotherms and low variation in K(OC) values across soils suggested partitioning-dominated sorption of the VMS. Compared with traditional hydrophobic organic compounds, K(OC) values for the VMS compounds were significantly lower than expected on the basis of their octanol-water partition coefficients. A linear free energy relationship analysis showed that these differences could be rationalized quantitatively in terms of the inherent characteristics of the VMS compounds, combined with the differences in solvation properties of organic matter and octanol"
Keywords:		Adsorption Carbon/chemistry Kinetics Octanols/chemistry Siloxanes/*analysis Soil/chemistry Solubility United Kingdom Volatile Organic Compounds/*analysis Water/*chemistry Environmental partitioning Fate and transport Linear free energy relationship Organi;
Notes:		"MedlineKozerski, Gary E Xu, Shihe Miller, Julie Durham, Jeremy eng Research Support, Non-U.S. Gov't 2014/05/28 Environ Toxicol Chem. 2014 Sep; 33(9):1937-45. doi: 10.1002/etc.2640. Epub 2014 Aug 4"