Organic Contaminants

Sorption From Water Solution 731 General Equilibrium Characteristics

We begin by looking at the sorption data for relatively nonpolar organic compounds (solutes), and then look at the data for relatively polar organic compounds, because of some characteristic differences in their behaviors. Whereas the demarcation between polar and nonpolar compounds is not straightforward, polar compounds are considered to be those that possess significant polar groups in their molecular structures, and nonpolar compounds those that contain little or no polar groups. Some...

Substituent Contributions To Partition Coefficients

Partition Water And Organic Solvent

The concept of substituent contribution to the partition coefficient of a substituted molecule with respect to a parent molecule was introduced by Fujita et al. (1964) in medicinal chemistry and pharmaceutical science for estimating the Kow values of some drugs and other chemicals in the absence of their experimental values. It has gained relatively good success when applied to small and structurally simple molecules but has had less success when extended to more complicated molecules. To...

Influence of Dissolved and Suspended Natural Organic Matter

For many highly water-insoluble compounds, the term log (yw gj) often has a more significant impact on the logKom value in soil-water systems Eq. (7.11) than, say, on logKow values in octanol-water systems Eq. (5.1) . In soil-water mixtures, the term yw gj expresses the enhancement of solute concentration or solubility by a given level of dissolved and or suspended (colloidal) organic matter in water derived from soil sediment or other sources (i.e., gjgt C*JCe S*JSw), as described later. Even...

Octanolwater Systems

Among current studies of the partition effects of nonionic organic compounds in various solvent-water mixtures, the partition coefficients in octanol-water mixtures have received the utmost attention because of the observed correlations between the octanol-water partition coefficients and the partition effects with natural organic substances and biological components. Part of the reasons for the success of n-octanol as a surrogate for natural organic matter and or biological components has to...

Bibliography

E., Jr., Department of Chemistry, University of North Texas, Denton, Texas, personal communication 1998 . Acree, W. E., Jr. and J. H. Rytting, Solubility in binary-solvent systems. Part IV. Prediction of naphthalene solubilities using the UNIFAC group contribution model, Int. J. Pharm. 13,197-204 1983 . Adamson, A. W., Physical Chemistry of Surfaces, 2nd ed., Wiley, New York, 1967. Aiken, G. R. and R. L. Malcolm, Molecular weight of aquatic fulvic acids by vapor pressure osmometry,...

Influences of Mineral Matter Organic Matter and Water

To better understand the sorption of an organic compound to a soil or a natural solid under a particular system condition, it is helpful to have a brief overview of important and unique sorption characteristics in relation to the soil or solid composition and the water content associated with it. The highly heterogeneous nature of soil samples from different geographic sources greatly complicates the resulting sorption of organic contaminants. This made it a formidable challenge for scientists...

Lipid Water Partition Coefficient

Information on the solute partition behavior in lipid-water mixtures is essential to an understanding of contaminant bioconcentration potentials in natural aquatic environments. Meanwhile, it offers a direct account of a chemical's lipophilicity as well as an important reference to the fish bioconcentration factor (BCF) observed. As before, we select triolein as the model lipid in our analysis of the lipid-water partition coefficient. The preceding section showed evidence that Raoult's law is...

Theoretical Considerations

Consider first the simpler case of a partition-limited model for the plant uptake of nonionic contaminants from a soil-free nutrient solution by passive transport through the plant vascular system. Here water is both the solvent for the contaminant and the medium that carries it to plant roots (and to other water-contacted surfaces) and eventually to other parts of the plant via the plant vascular system. The overall plant uptake process is driven by the external-water concentration and is...

Cohesive Energy Density And Solubility Parameter

The sum of the various attractive forces that hold the molecules of a substance in a liquid or solid state is called the coheSive energy. The magnitude of this energy is not only a function of the molecular makeup but also of the molecular size. Types of cohesive forces that operate in uncharged liquids and solids include the induced dipole-induced dipole force (also called the London force), the dipole-dipole force (the Debye force), the dipole-induced dipole force (the KeeSom force), and the...

Time Dependence Of Contaminants In Plants

A subject of considerable interest to the plant uptake of a contaminant is the time dependence of the contaminant level in a specific part of the plant. In the practice of bioremediation by planting, this would determine the efficiency of a plant in taking up a target contaminant with time from an external source. Although not well established at this time, the preceding data analysis leads to the expectation that the change with time of the in-plant contaminant level should be a function of...

Heptanewater Systems

The n-heptane water mixture offers an extreme but instructive system for examining important differences in the partitioning of polar and nonpolar compounds into a highly nonpolar organic phase. As with the octanol-water system, the molecular-size differences between most solutes and heptane are usually not too large to negate the use of Raoult's law for treating solute partition with heptane. Note here that the mutual solubility of heptane and water is very small at room temperature, the...

Behavior of PAHs versus Other Nonpolar Contaminants

Although the Koc values of many nonpolar contaminants can be estimated with sufficient accuracy from their physicochemical properties, such as Kow or Sw, the selection of a proper correlation for estimation is, however, complicated by the inconsistency of published correlations for selected nonpolar compounds on soils and sediments. A particular case in point is the inconsistency of the correlations for polycyclic aromatic hydrocarbons (PAHs) relative to other nonpolar organic compounds. For...