Solvent partitioning in soils

A procedure is available to determine partitioning organic chemicals between water and soil or sediment. By measuring sorption coefficients for specific solids, a single value is obtained which can be used to predict partitioning under a variety of conditions. The 

Standard specifications are designed to set criteria for commercial solvents which can be used to determine the compliance of a solvent sample. Because applications of solvents differ very widely, the selected criteria are also different for different groups of solvents. Table 15.1.1 is a compiled list of parameters all of which can be found in solvent specifications. The most common parameters used to characterize solvent include acidity, appearance, color, concentration of main component, distillation range, dry point, initial boiling point, and specific gravity. The methods of determining these parameters are found in fliis chapter. 

The list of references includes information on specifications for various solvents. Solvents in this list are arranged into groups alcohols,aromatic hydrocarbons, other hydrocarbons,ketones, esters, glycol, and chlorine-containing sol-vents. -  

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Analytical methods for parent chloroacetanilide herbicides in soil typically involve extraction of the soil with solvent, followed by solid-phase extraction (SPE), and analysis by gas chromatography/electron capture detection (GC/ECD) or gas chromatog-raphy/mass spectrometry (GC/MS). Analytical methods for parent chloroacetanilides in water are similarly based on extraction followed by GC with various detection techniques. Many of the water methods, such as the Environmental Protection Agency (EPA) official methods, are multi-residue methods that include other compound classes in addition to chloroacetanilides. While liquid-liquid partitioning was used initially to extract acetanilides from water samples, SPE using... 

The availability of contaminating organic compounds is also often described by their partition coefficient between water and a solvent, most often octanol. The more soluble a compound is in water, the more available for decomposition. By describing the solubility ratio, the relative rates of organic compound decomposition in soil can be estimated [3],... 

Furthermore, air-organic solvent partition constants, in particular the air-octanol partition constant, are widely used to evaluate and/or predict the partitioning of organic compounds between air and natural organic phases. Such organic phases are present, for example, in aerosols or soils (Chapters 9 and 11) or as part of biological systems (Chapter 10). 

Hewitt, A.D., Comparison of sample preparation methods for the analysis of volatile organic compounds in soil samples solvent extraction vs. vapor partitioning, /. Environ. Sci. Technol., 32(1), 143-149, 1998. 

Kawata et al. [ 128] have described the effects of headspace conditions on recoveries of volatile organic compounds from sediments and soils. Hewitt [129] compared three vapour partitioning headspace and three solvent extraction methods for the preparation of soil samples for volatile organic carbon determination in soils. Methanol extraction was the most efficient method of spiked volatile organic carbon recovery, which depended on the soil organic carbon content, the octanol-water partitioning coefficients of analytes and the extraction time. 

Owing to the impossibility of compiling partition coefficients for a substance into every possible set of solvents/phases, a reference that is commonly accepted is the octanol/water partition coefficient, Kj0tW. This solvent (i.e., the 1-octanol) is a good reference choice as it mimics (to a reasonable extent) the solvent behavior of lipids in biota as well as that of humic substances in soils. Extensive tables of Kio w values are readily available (see for example, the CRC Handbook for Chemistry and Physics). Such data help predict the environmental fate of many substances (see Casey and Pittman, 2005). 

A large number of organic chemical pollutants are hydrophobic, literally afraid of water. These chemicals have limited solubility in water but do tend to dissolve easily into oils, fats, nonpolar organic solvents, and organic carbon in the soil. To a first approximation, the partition coefficient for many hydro-phobic chemicals in soil is not especially sensitive to the exact source or nature of the organic carbon. Accordingly, Koc, the organic carbon-water partition coefficient, can be used to estimate the extent of sorption. Koc can be expressed as... 

Trichloroethane will enter the atmosphere from its use in the manufacture of vinylidene chloride and its use as a solvent. Once in the atmosphere, 1,1,2-trichloroethane will photodegrade slowly by reaction with hydroxyl radicals (half-life 24 to 50 days in unpolluted atmospheres and within a few days in polluted atmospheres). The soil partition coefficient of 1,2-trichloroethane is low and it will readily leach in the case of eventual, very slow biodegradation. Bioconcentration is not a significant process. It will also be discharged in wastewater associated with these uses and in... 

The effect of dissolved organic matter on the solubility of DDT and two PCB congeners is illustrated in Figure 2.8. This study demonstrates that the solubility of the chlorinated hydrocarbon was increased with the amount of soil humic acid added. It must be emphasized that this increase does not result from an effect on the solvent but it is due to the association of the solute with the dissolved humic acid. With these hydrophobic compounds it would appear that the association is due to their partitioning into rather than adsorption onto the humic acid since the two PCB congeners do not compete, that is, the trichlorobiphenyl does not reduce the association of the pentachlorobiphenyl. (The partitioning process is discussed in more detail in the analysis of the sorption in soil.)... 

Hodgson, J.F., Geering, H.R., Norvell, W.A., 1965. Micronutrient cation complexes in soil solution Partition between complexed and uncomplexed forms by solvent extraction. Soil Sci. Soc. Am. Proc. 29, 665-669. 

Hartley 46) speculated that a solvent action of the oily constituents of the organic matter might be important for soil uptake. Swoboda and Thomas 98) expressed a similar view in their study of parathion on soil. The chromatographic sorption model of Lambert (59) is compatible with the idea of solute partitioning between soil organic matter and water. 

Adsorption is a physicochemical process whereby a dissolved solvent may be concentrated at solid-liquid interfaces such as water in contact with soil or sediment. In general, the extent of adsorption is inversely proportional to solubility sparingly soluble solvents have a greater tendency to adsorb or partition to the organic matter in soil or sediment (see Soil, 17.1.3.2). 

As discussed in 17.1.2.4., adsorption by soil components can remove solvents dissolved in water. Furthermore, the rate of movement of dissolved solvents through soil may be retarded by adsorption-desorption reactions between the solvents and the solid phases. The partitioning of solvents between the liquid phase and soil is usually described by an adsorption isotherm. The adsorption of solvents may be described by the Freundlich Equation ... 

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