Organic carbon normalized distribution

Kqc Soil organic carbon normalized distribution coefficient... 

Higgins and Luthy [23] examined the organic carbon normalized distribution coefficients (Koc) of eight long chain PFC (four PFCA, two PFSA and two perfluorooctane sulfonamide acetic acids) with batch experiments (initial PFC concentrations 0.5-100 pg/L) (results see Table 1). They displayed the dependency of sorption and chain length, showing that the log Kqc values increase by between 0.3 and 0.6 log units with each additional CF2 moiety. When comparing the results... 

Table 5. Phenanthrene distribution (Kn) and organic carbon normalized partition (Km) coefficients to sorbed surfactants on kaolinite for varying solution chemistry conditions.a... 

Figure 7. Effect of pH on phenanthrene distribution (A. 0) and organic carbon normalized partition (/ ) coefficients for sorbed SDS, The ionic strength was 0.1 M NaCl, and the kaolinite concentration was 100 g/L. Error bars for some data points are smaller than the symbols. The solid line is the average Kx value for pH values above the PZC of kaolinite, The predicted value is based on an equation from Schwarzenbach et al. (1993), Adapted from Ko et al. (1998a).

It may be deduced from KP = Koc x foc that partition coefficients of hydro-phobic organic compounds in general are dependent upon the chemical of interest (compound-specific properties affect the value of Koc) and the matrix properties of the medium in which it resides. In addition to the fraction of organic carbon present in the sorption phase, additional environmental factors affect partitioning. These factors include temperature, particle size distribution, the surface area of the sorbent, pH, ionic strength, the presence of suspended material or colloidal material, and the presence of surfactants. In addition, clay minerals may act as additional sorption phases for organic compounds. Nevertheless, organic carbon-normalized partition... 

The Kd can in turn be used to compute that is, the distribution coefficient normalized to the percent organic carbon (%OC) present in the sorbent [Eq. (3.20)] ... 

A clear understanding of the solubility properties of various organic compounds, including PPCPs, directly relates to the partitioning of these compounds as defined by several physical properties such as the distribution coefficient normalized to the percent organic carbon (Koc), octanol-water partition coefficient base... 

For air-water systems, this equation is known as Henry s law. For solids-water systems, the equilibrium constant is known as the partition coefficient (Ky) or distribution constant (KA). Partition coefficients are available for many organic chemicals from laboratory and field measurements. As organic carbon (OC) present in water (dissolved organic carbon, or DOC), sediment, or soil is the main sink for hydrophobic organic contaminants, the partition coefficients for these compounds are often adjusted (normalized) with respect to the organic carbon content of these compartments ... 

The value of the distribution coefficient, K, varies with several soil properties, most notably the organic carbon content. This has led to the definition of a normalized sorption coefficient, Koc, which is calculated as (12) ... 

Several researchers have found that if the distribution coefficient is normalized relative to the aquifer matrix total organic carbon content, much of the variation in observed Kj values between different soils is eliminated. Distribution coefficients normalized to total organic carbon content are expressed as Kqc- Tbe following equation gives the expression relating to K , ... 

Chemicals in water can sorb to sediment or soil in a reversible process that reflects the attraction and adhesion of molecules to solids. (Less commonly considered in environmental mass balances, some air pollutants can sorb to particulates in the atmosphere.) The n-octanol/water partition coefficient (K ) of a substance provides a crude indication of the tendency to partition to solids from water a high value indicates that a substance is hydro-phobic/lipophilic and would tend to sorb to solids. More sophisticated tests determine a distribution coefficient (KJ or adsorption isotherm to relate the concentration in solution to the concentration sorbed to solids. The sorption coefficient is the ratio between the concentration of a chemical in soil to the concentration in water which is in contact with the soil. Normalized to the organic carbon content of the soil, this coefficient becomes (K = I i/ fraction organic carbon in soil) [4]. 

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