Hydrophobic substance sorption

The "Sorption" of Hydrophobic Substances to Solid Materials that contain Organic Carbon... 

The sorption of non-polar organic hydrophobic substances to solid material that contain organic carbon must be interpreted as "absorption", i.e., a "dissolution" of... 

Rocks may be hydrophobic or hydrophilic and this property is closely related to the extent of sorption. In contrast to hydrophilic materials, hydrophobic substances have no free valences or electrostatic charge available at their surfaces. Hence, neither hydrated water molecules nor dissolved species can be bound to the surface and in the extreme case, could largely prevent the wetting of the surface with aqueous solution. 

Linear isotherms are typically observed for the (ab)sorption of hydrophobic substances on organic or organically coated particles. In this case the hydro-phobic substance becomes absorbed as if the organic matter were the solvent. ... 

SORPTION OF HYDROPHOBIC SUBSTANCES ON ORGANIC CARBON-BEARING PARTICLES... 

Sorption of Hydrophobic Substances 583 Table 9.2. Types of Polyelectrolytes... 

Good wettability is essential for membranes that serve as separators in electrochemical cells. While fluorocarbon polymers are generally known to be quite hydrophobic substances, these membranes are certainly an exception. They sorb water rapidly even at room temperature. The sorption rates of water and other... 

It is seen, that the curves are entirely different from those of SO2 (Fig. 23a). We shall first discuss the initial part below a reh spresure of 0.3, where the quantity of water absorbed remains below 10 mg per g of carbon. This affords a striking contrast with the sorption of a substance like benzene of which almost 50% of the saturation quantity is already absorbed at a rel. pressure of 0.001. The affinity of carbon as a hydrophobic substance is small towards water and considerable towards many organic compounds. 

Contaminants with very low water solubilities (e.g. polycyclic aromatic hydrocarbons) play an important role in risk assessment of dangerous wastes and development of soil remediation. The mobility of such hydrophobic substances can be strongly affected by the existence of carriers (e.g. dissolved organic carbon), which can adsorb the contaminant and thereby enhance or reduce its velocity. The numerical simulation of the spreading of these contaminants, requires the solution of reactive transport equations for all involved components, coupled by the contaminant s sorption to the carrier. Our development is based on a model [2], in which all the carrier s influence on the contaminant transport is contained in an effective adsorption isotherm, depending on the carrier concentration and thereby also on space and time. First we shortly summarize the modelling of reactive transport of a single component (carrier, contaminant, carrier bound contaminant) in a porous medium, then in section 3 we combine the two equations for the contaminant components. The properties of the contaminant s effective isotherm and its influence on the transport equation are discussed in section 4. 

Georgi A, Trommler U, Reichl A, Kopinke F-D (2008) Influence of sorption to dissolved humic substances on transformation reactions of hydrophobic organic compounds in water. Part II hydrolysis reactions. Chemosphere 71 1452-1460... 

Historically, organic environmental pollutants were hydrophobic, often persistent, neutral compounds. As a consequence, these substances were readily sorbed by particles and soluble in lipids. In modern times, efforts have been made to make xenobiotics more hydrophilic - often by including ionisable substituents. Presumably, these functional groups would render the compound less bioaccumulative. In particular, many pesticides and pharmaceuticals contain acidic or basic functions. However, studies on the fate and effect of organic environmental pollutants focus mainly on the neutral species [1], In the past, uptake into cells and sorption to biological membranes were often assumed to be only dependent on the neutral species. More recent studies that are reviewed in this chapter show that the ionic organic species play a role both for toxic effects and sorption of compounds to membranes. 

Murphy, E.M., Zachara, J.M., and Smith, S.C. Influence of mineral-bound humic substances on the sorption of hydrophobic organic compounds. Environ. Scl Technol, 24(10) 1507-1516, 1990. 

The partition coefficient Kq of an organic compound in the 1-octanol/water system is used to assess the bioaccumulation potential and the distribution pattern of drugs and pollutants. The partition coefficient of imidazole and ILs strongly depends on the hydrogen bond formed by these molecules and is less than one due to the high solubility in water. The low value of the 1-octanol/water partition coefficient is required for new substances, solvents, insecticides to avoid bioaccumulation. Kqw is an extremely important quantity because it is the basis of correlations to calculate bioaccumulation, toxicity, and sorption to soils and sediments. Computing the activity of a chemical in human, fish, or animal lipid, which is where pollutants that are hydrophobic will appear, is a difficult task. Thus, it is simpler to measure the 1-octanol/water partition coefficient. This parameter is used as the primary parameter characterizing hydrophobisity. 

Association of surfactant molecules onto humic substances is also termed sorption and has been given some attention. In the case of cationic alkyl trimethyl and dimeth-yldioctadecyl ammonium surfactants (Versteeg and Shorter, 1992), the presence of dissolved organic carbon in the water significantly reduced the toxicity of these compounds to fathead minnows. The effect of toxicity reduction increased with increasing hydrophobicity. For the anionic surfactant LAS, this mitigating effect was less pronounced (Traina et al., 1996). 

Wu and Gschwend (1986) reviewed and evaluated several kinetic models to investigate sorption kinetics of hydrophobic organic substances on sediments and soils. They evaluated a first-order model (one-box) where the reaction is evaluated with one rate coefficient (k) as well as a two-site model (two-box) whereby there are two classes of sorbing sites, two chemical reactions in series, or a sorbent with easily accessible sites and difficultly accessible sites. Unfortunately, the latter model has three independent fitting parameters kx, the exchange rate from the solution to the first (accessible sites) box k2, the exchange rate from the first box to the... 

Humic substances that constitute the hydrophobic part of DOM have a high capacity for sorption of hydrophobic organic pollutants. Humic acids have a better sorption capacity than fulvic acids, and thus reduce bioaccumulation much better than fulvic acids. 

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