Partitioning soil/water

Keywords Partitioning Soil Water Sorption Diffusion Interphase mass transfer ... 

UNSAT-H simulates plant transpiration with a PET concept. The model partitions plants removal of soil-water between soil layers based on (1) distribution of plant roots within the soil profile for cheatgrass (an invading and weedy grass species found in dry regions of Washington State) or (2) the user may supply other functions. The user must enter soil-water parameters that describe the limits for plant extraction of water from each layer of soil. The model also uses the same daily value pattern for the LAI for each year. 

Soil Diffusion. Water-soluble material In the soil Includes material dissolved In the soil water, material dissolved In the soil air, and material adsorbed to the soil solids. The soil water-soil air equilibrium partitioning Is described by Henry s law ... 

The bioavailability of trace elements in soil-water-plant ecosystems of arid zones is largely determined by their partitioning between solution and solid-phase components. The redistribution and transformation of trace elements among solid-phase components under various biogeochemical conditions strongly adjust their lability and bioavailability. Soluble, exchangeable and organically bound forms are bioavailable to plants. The carbonate bound fraction represents a reservoir of potentially bio-available trace elements to plants. In paddy soils, the amorphous Fe/Al oxide fraction contributes to trace element availability as well. 

Narwal R.P., Singh B.R. Effect of organic materials on partitioning, extractability and plant uptake of metals in an alum shale soil. Water Air Soil Pollut 1998 103 405M21. 

Briggs GG (1981) Theoretical and experimental relationships between soil adsorption, octanol-water partition coefficients, water solubilities, bioconcentration factors, and the parachor. J Agric Food Chem 29 1050-1059... 

The calculation is illustrated in Table 1.5.5 for pentachlorophenol. The experimental aqueous solubility is 14.0 g/m3 at a pH of 5.1. The environmental pH is 7. Higher environmental pH increases the extent of dissociation, thus increasing the Z value in water, increasing the apparent solubility, decreasing the apparent KqW and Henry s law constant and the air-water partition coefficient, and decreasing the soil-water partition coefficient. 

Calculated Zw values and some partition coefficients at different environmental pHs for pentachlorophenol (PCP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and p-cresol at 25°C. Kaw is the air-water partition coefficient and Ksw is the soil-water partition coefficient... 

The Level I calculation suggests that if 100,000 kg (100 tonnes) of benzene are introduced into the 100,000 km2 environment, 99% will partition into air at a concentration of 9.9 x 10-7 g/m3 or about 1 pg/rn3. The water will contain nearly 1% at a low concentration of 4 pg/rn3 or equivalently 4 ng/L. Soils would contain 5 x 10-6 pg/g and sediments about 9.7 x 10 6 pg/g. These values would normally be undetectable as a result of the very low tendency of benzene to sorb to organic matter in these media. The fugacity is calculated to be 3.14 x 10-5 Pa. The dimensionless soil-water and sediment-water partition coefficients or ratios of Z values are 2.6 and 5.3 as a result of a Koc of about 55 and a few percent organic carbon in these media. There is little evidence of bioconcentration with a very low fish concentration of 3.0 x FT5 pg/g. The pie chart in Figure 1.7.6 clearly shows that air is the primary medium of accumulation. 

The Level I calculations for environmental pHs of 5.1 and 7 suggest that if 100,000 kg (100 tonnes) of pentachlorophenol (PCP) are introduced into the 100,000 km2 environment, most PCP will tend to be associated with soil. This is especially the case at low pH when the protonated form dominates. Very little partitions into air and only about 1% partitions into water. Soil contains most of the PCP. Sediments contain about 2%. There is evidence of bioconcentration with a rather high fish concentration. Note that only four media (air, water, soil and bottom sediment) are depicted in the pie chart therefore, the sum of the percent distribution figures is slightly less than 100%. The air-water partition coefficient is very low. As pH increases, dissociation increases and there is a tendency for partitioning to water to become more important. Essentially, the capacity of water for the chemical increases. Partitioning to air is always negligible. 

Krauss, M., Wilcke, W. (2001) Predicting soil-water partitioning of polycyclic aromatic hydrocarbons and polychlorinated biphenyls by desorption with methanol-water mixtures at different temperatures. Environ. Sci. Technol. 35, 2319-2325. 

Silver occurs naturally in several oxidation states, the most common being elemental silver (Ag°) and the monovalent ion (Ag+). Soluble silver salts are, in general, more toxic than insoluble salts. In natural waters, the soluble monovalent species is the form of environmental concern. Sorption is the dominant process that controls silver partitioning in water and its movements in soils and sediments. As discussed later, silver enters the animal body through inhalation, ingestion, mucous membranes, and broken skin. The interspecies differences in the ability of animals to accumulate, retain, and eliminate silver are large. Almost all of the total silver intake is usually... 

In the vadose (unsaturated) zone, liquid organic compounds partition into four distinct but related phases NAPL adsorbed onto soil particles, free-phase NAPL, soluble constituents in soil water, and vapor-phase components as part of the soil... 

The transport processes that may move disulfoton from soil to other media are volatilization, leaching, runoff, and absorption by plants. Volatilization of disulfoton from wet soil may be greater than from relatively dry soil (Gohre and Miller 1986). Like other pesticides, disulfoton in soil partitions between soil-sorbed and soil-water phases (Racke 1992). This latter phase may be responsible for the volatilization of disulfoton from soil however, due to the low Henry s law constant value, the rate of disulfoton volatilization from the soil-water phase to the atmosphere would be low. 

Leaching processes introduce hydrocarbon into the water phase by solubility and entrainment. Leaching processes of petroleum products in soils can have a variety of potential scenarios. Part of the aromatic fraction of a petroleum spill in soil may partition into water that has been in contact with the contamination. 

Girvin, D.C. and Scott, A.J. Polychlorinated biphenyl sorption by soils measurement of soil-water partition coefficients at equilibrium, Chemosphere, 35 (9) 2007-2025. 1997. 

Liao, Y.-Y., Wang, Z. T., Chen, J.-W.. Han. S.-K.. Wang. L. S.. Lu. G. Y.. and Zhao. T.-N. The prediction of soil sorption coefficients of heterocyclic nitrogen compounds by octanol/water partition coefficient, water solubility, and by molecular connectivity indices. Bull Environ. Contam. Toxicol, 56(5) 711-716. 1996. 

As discussed earlier, the proportion of the molecules in the vapor state within the soil near a source is around 6 orders of magnitude less than the sorbed or dissolved portions. This condition was stated for 50% moisture saturation. For extremely dry soils, this ratio becomes even more pronounced. Phelan and Barnett defined a soil-air partitioning coefficient, Kd>, in a manner parallel to the soil-water partitioning coefficient, Kd [12] ... 

Sorption of soil Advection - diffusion Equilibrium soil-water partitioning... 

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