Hydrophobic organic contaminants partitioning

Swackhamer DL, Skoglund RS (1991) The role of phytoplankton in the partitioning of hydrophobic organic contaminants in water. In Baker RA (ed) Organic substances and sediments in water, vol II. Lewis, Chelsea, MI, p 91... 

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

Abstract Partitioning of two hydrophobic organic contaminants (HOCs), phenanthrene... 

Ksoc, as defined in the previous paragraph, represents the effectiveness of the sorbed surfactant to serve as a partition medium for a hydrophobic organic contaminant relative to the native soil organic matter. Mathematically, K is equivalent to... 

Dissolved organic matter (DOM) is ubiquitous to natural waters and is known to undergo a number of reactions of environmental interest. Among these reactions neutral hydrophobic organic contaminants (HOCs) can partition into or be bound to DOM. This process can significantly alter the... 

Ko, F.C., Baker, J.E., 1995. Partitioning of hydrophobic organic contaminants to resuspended sediments and plankton in the mesohaline Chesapeake Bay. Environ. Sci. Technol. 49, 171-188. 

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 ... 

Sorption of organic contaminants onto aquifer solids is frequently described as a partitioning process, where the hydrophobic organic compound partitions into natural organic material associated with the aquifer solids [8]. Sorption can be characterized as either an equilibrium or rate-limited phenomenon. Equilibrium sorption can be modeled as either a linear or non-linear process. Equilibrium sorption may be assumed when the flow of groundwater and other processes affecting contaminant transport are slow compared to the rate of sorption. In this event the sorption of the contaminant can be considered instantaneous. If we assume equilibrium sorption, the relationship between sorbed and aqueous contaminant concentrations may be described by a sorption isotherm. 

In some sorption cases 1/n equals 1. When this condition is met, a plot of -SC versus C will produce a straight line with KD as slope (C-type isotherm Fig. 4.16). This type of isotherm best describes soil sorption of hydrophobic organics (e.g., chlorinated hydrocarbons) (Fig. 4.17). The linearity of such data can be explained by the schematic model in Figure 4.18. In this model, (linear partition model), the hydrophobic organic contaminant distributes itself linearly between hydrophobic organic matter adsorbed on an inorganic mineral particle and solution. Linearity... 

The Linear Partitioning Model. Several conceptual and empirical models have been proposed to quantify sorption of hydrophobic organic contaminants (HOCs) by soils and sediments. The simplest of these is the linear partitioning model, in which the solid-phase solute concentration, is assumed to be directly proportional to the aqueous-phase solute concentration, Q i.e.,... 

Most conventional organic contaminants are fairly hydrophobic and thus exhibit a low but measurable solubility in water. Solubility is often used to estimate the air-water partition coefficient or Henry s law constant, but this is not possible for miscible chemicals indeed the method is suspect for chemicals of appreciable solubility in water, i.e., exceeding 1 g/100 g. Direct measurement of the Henry s law constant is thus required. 

Properties of surfactant and cosolvent additives affect the rate of apparent solubilization of organic contaminants in aqueous solutions and may serve as a tool in remediation of subsurface water polluted by NAPLs. Cosolvents (synthetic or natural) are organic solutes present in sufficient quantities in the subsurface water to render the aqueous phase more hydrophobic. Surfactants allow NAPLs to partition into the... 

In a sediment system, the hydrolysis rate constant of an organic contaminant is affected by its retention and release with the sohd phase. Wolfe (1989) proposed the hydrolysis mechanism shown in Fig. 13.4, where P is the organic compound, S is the sediment, P S is the compound in the sorbed phase, k and k" are the sorption and desorption rate constants, respectively, and k and k are the hydrolysis rate constants. In this proposed model, sorption of the compound to the sediment organic carbon is by a hydrophobic mechanism, described by a partition coefficient. The organic matrix can be a reactive or nonreactive sink, as a function of the hydrolytic process. Laboratory studies of kinetics (e.g., Macalady and Wolfe 1983, 1985 Burkhard and Guth 1981), using different organic compounds, show that hydrolysis is retarded in the sohd-associated phase, while alkaline and neutral hydrolysis is unaffected and acid hydrolysis is accelerated. 

The hydrophobicity of an organic molecule is quantified by means of its partition coefficient between octanol and water (Kow)- Kow is equal to the ratio of compound concentrations at saturation in n-octanol and in water at equilibrium and at a specific temperature. n-Octanol possesses structural properties analogous to lipidic tissues of organisms, and so Kow allows evaluation of the lipophilic character of the contaminant and thus of its capacity to be accumulated in the lipidic tissues of living organisms. The Kow value of hydrophobic organic pollutants (HOPs) is higher than 100. They are nonpolar molecules with a low water solubility. Their weak solubility and their hydrophobicity... 

Temperature is a key parameter for controlling H or thereby strongly influencing air-water partitioning of chemicals in the environment. A good deal of effort is expended in deducing temperature-dependent H for contaminants of concern, which is not an easy task for low-polarity hydrophobic organic chemicals (HOCs) with poor solubility. 

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