Particle-Water Partitioning

Hudson, R. J. M. (1998). Modeling the fate of metals in aquatic systems the mechanistic basis of particle-water partitioning models, Crit. Rev. Anal. Chem., 28, 19-26. 

In the laboratory, we usually determine Kl2 from the slope of C versus C2 over a range of concentrations. Partition coefficients can be measured for essentially any two-phase system air-water, octanol-water, lipid-water, particle-water, and so on. In situ partition coefficients also can be measured where site-specific environmental conditions might influence the equilibrium phase distribution. 

It has been known for several decades that many chemicals preferentially associate with soil and sediment particles rather than the aqueous phase. The particle-water partition coefficient (Kp) describing this phenomenon is... 

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). 

Gelation of one or both phases interrupts partitioning of water and large size dispersed particles between the phases. This illustrates the nonequUibrium ... 

Morel F. M. M. and Gschwend P. M. (1987) The role of colloids in the partitioning of solutes in natural waters. In Aquatic Surface Chemistry Chemical Processes at the Particle—Water Interface (ed. W. Stumm). Wiley, New York, pp. 405 22. 

Many of the important chemical reactions controlling arsenic partitioning between solid and liquid phases in aquifers occur at particle-water interfaces. Several spectroscopic methods exist to monitor the electronic, vibrational, and other properties of atoms or molecules localized in the interfacial region. These methods provide information on valence, local coordination, protonation, and other properties that is difficult to obtain by other means. This chapter synthesizes recent infrared, x-ray photoelectron, and x-ray absorption spectroscopic studies of arsenic speciation in natural and synthetic solid phases. The local coordination of arsenic in sulfide minerals, in arsenate and arsenite precipitates, in secondary sulfates and carbonates, adsorbed on iron, manganese, and aluminium hydrous oxides, and adsorbed on aluminosilicate clay minerals is summarized. The chapter concludes with a discussion of the implications of these studies (conducted primarily in model systems) for arsenic speciation in aquifer sediments. 

When sorption-desorption processes are fast relative to particle settling, the effectiveness of the downward transport is related to the particle concentration, downward particle flux, and the particle-water partition coefficient for the pollutant in question. Rates of sorption-desorption may be limiting in some instances characteristic times for sorption-desorption then become important, along with the contact time available for interaction with particles. 

Table 2 List of the elements (with isotopes of half-life ti/2>1 day) in the U decay series with their scavenging residence time in deep and surface ocean and their estimated particle-water partition coefficient Kj, showing the relative mobility of U, Ra, and Rn...

As discussed above, SVOCs are removed from the atmosphere and transported to the waters by precipitation scavenging of atmospheric vapors and particles, which are incorporated into the rain within or below the clouds. After SVOCs are deposited into the bulk seawater, partitioning in water column can affect the distribution of pollutants between the dissolved aqueous and the solid phases and eventually impact the fate of these compounds in oceans (Luo et al. 2004). In addition, air-sea exchange can make SVOCs diffuse across the air-sea interface however, the sea surface microlayer (SML), a unique compartment at the air-sea boundary defined operationally as the upper millimeter (1-1,000 pm)... 

Sjbdin A, Carlsson H, Thuresson K et al (2000) Flame retardants in indoor air at an electronics recycling plant and at other work environments. Environ Sci Technol 35 448-454 Sobek A, Gustafsson O, Hajdu S et al (2004) Particle-water partitioning of PCBs in the photic zone a 25-month study in the open Baltic Sea. Environ Sci Technol 38 1375-1382 Sbderstrbm G, Sellstrbm U, de Wit CA et al (2004) Photolytic debromination of decabromod-iphenyl ether (BDE 209). Environ Sci Technol 38 127-132 Strandberg B, Dodder NG, Basu I et al (2001) Concentrations and spatial variations of polybrominated diphenyl ethers and other organohalogen compounds in Great Lakes air. Environ Sci Technol 35 1078-1083... 

Axelman, J., D. Broman C. Naf, 1997. Field measurements of PCB partitioning between water and planktonic organisms Influence of growth, particle size, and solute-solvent interactions. Environ. Sci.Technol. 31 665-669. 

The cleaning process proceeds by one of three primary mechanisms solubilization, emulsification, and roll-up [229]. In solubilization the oily phase partitions into surfactant micelles that desorb from the solid surface and diffuse into the bulk. As mentioned above, there is a body of theoretical work on solubilization [146, 147] and numerous experimental studies by a variety of spectroscopic techniques [143-145,230]. Emulsification involves the formation and removal of an emulsion at the oil-water interface the removal step may involve hydrodynamic as well as surface chemical forces. Emulsion formation is covered in Chapter XIV. In roll-up the surfactant reduces the contact angle of the liquid soil or the surface free energy of a solid particle aiding its detachment and subsequent removal by hydrodynamic forces. Adam and Stevenson s beautiful photographs illustrate roll-up of lanoline on wood fibers [231]. In order to achieve roll-up, one requires the surface free energies for soil detachment illustrated in Fig. XIII-14 to obey... 

The solubihty of hydrophobic substances in, or their absorbabiUty on suspended particles, on sediments, on biota, or on soil particles can be related to the solubihty of these substances in organic solvents. The solvent -octanol, CH2(CH2)yOH, is a kind of surrogate for many kinds of environmental and physiological organic substances and has become a reference phase for organic phase water partitioning of organic solutes. 

With the help of equiUbrium constants, the extent of adsorption can be predicted as a function of pH and solution variables (7,25,43). Based on this model, the partitioning of metal ions and of ligands (organic and inorganic anions between water and pelagic clays and suspended particles) can be explained. 

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