Hydrophobicity, environmental partition coefficients

A series of experiments was also conducted by Bowman et al. [34] to ascertain the effects of differing environmental factors on the sediment-water interactions of natural estrogens (estradiol and estrone) under estuarine conditions. Sorption onto sediment particles was in this case relatively slow, with sorption equilibrium being reached in about 10 and 170 h for estrone and estradiol, respectively. On the other hand, true partition coefficients calculated on colloids were found to be around two orders of magnitude greater that those on sediment particles. Hence, it was concluded that under estuarine conditions, and in comparison to other more hydrophobic compounds, both estrone and estradiol... 

De Bruijin J, Busser F, Seinem W, et al. 1989. Determination of octanol water partition coefficients for hydrophobic organic chemicals with the "slow-stirring" method. Environmental Toxicology and Chemistry 8 499-512. 

If the activity coefficient is relatively small, i.e. <20, it is likely that the liquid is miscible with water and no solubility can be measured. The relevant descriptor of hydrophobicity in such cases is the activity coefficient. Correlations of other environmental partitioning properties with solubility are then impossible. 

For neutral organic compounds, in soils having a low clay/organic carbon ratio, sorption coefficients tend to increase as the hydrophobicity of the compound increases. Aqueous solubility or octanol/ water partition coefficients often are used as indicators of a compound s hydrophobicity. An increase in polarity, number of functional groups, and ionic nature of the chemical will increase the number of potential sorption mechanisms for a given chemical (Garbarini and Lion, 1985). For ionizable compounds, pKa is of particular importance because it determines the dominant form of a chemical at the specific environmental pH. 

Gschwend, P. M., and S. Wu. 1985. On the constancy of sediment-water partition coefficient of hydrophobic organic pollutants. Environmental Science and Technology 19 90. 

Karickhoff SW, Brown DS. 1979. Determination of octanol/water distribution coefficients, water solubilities, and sediment/water partition coefficients for hydrophobic organic pollutants. No. EPA-660/4-79/032. Athens (GA) US Environmental Protection Agency. 

As PFSAs and PFCAs are both hydrophobic and oleophobic, and form multiple layers when mixed with water and hydrocarbons [49], i ow values are not appropriate or relevant for these PFCs [26]. Similarly, other partition coefficients and traditional environmental fate models based on air, water and octanol partitioning are not suitable for PFSAs and PFCAs. 

Furthermore, an empirical hydrophobicity parameter derived from measurements of the distribution of a solute between two immiscible liquids should be mentioned cf. Section 2.2.7 dealing with hydrophobic interactions. The hydrophobic or lipophilic character of organic compounds plays an important role in their abihty to interfere with biochemical systems. Therefore, systematic efforts have been made to obtain numerically defined constants to assess the hydrophobic character of organic compounds. A hydrophobicity parameter which has proven quite valuable in the fields of toxicology, pharmacology, and environmental science is the Hansch-Leo 1-octanollwater partition coefficient TiTo/w or Pq/w as defined in Eq. (7-12),... 

Because the relative difference in the terms polar and nonpolar is somewhat undefined, a general parameter to define hydrophobicity is useful. Such a parameter is the octanol-water partition coefficient, Poet, which was defined earlier in this chapter. This parameter plays an important role in correlating phenomena of physicochemical, biological, and environmental interest. Many log Foot values are available in the literature and calculation methods have been reported. Hennion and Pichon (1994) define polarity from the log scale, with values below 1 as polar, 1 to 3 as moderately polar, and above 3 as nonpolar. 

Karickhoff, S.W. and D.S. Brown, Determination of Octanol/Water Distribution Coefficients, Water Solubilities, and Sediraent/Water Partition Coefficients for Hydrophobic Organic Pollutants, Report No. EPA-600/4-79-032, U.S. Environmental Protection Agency, Athens. GA (1979). 

The Henry s law constant is an important criteria in determining the extent to which an organic compound will distribute into the atmosphere from water and vice versa. Another important environmental process is the extent to which a compound will distribute into a hydrophobic region. It will be shown that soil organic matter controls sorption of organic compounds in soil, while movement into an organism involves passage across the hydrophobic barrier of the membrane. This tendency is indicated by the octanol-water partition coefficient, Xqw... 

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