Soil components

Models of chemical reactions of trace pollutants in groundwater must be based on experimental analysis of the kinetics of possible pollutant interactions with earth materials, much the same as smog chamber studies considered atmospheric photochemistry. Fundamental research could determine the surface chemistry of soil components and processes such as adsorption and desorption, pore diffusion, and biodegradation of contaminants. Hydrodynamic pollutant transport models should be upgraded to take into account chemical reactions at surfaces. 

As noted, the alkaloid yield from the Beocin plants was low, which the authors suggested might be caused by the poor soil in which the plants were growing (Popovic et ah, 1992). One could ask whether the soil conditions to which they refer might be influential in the overall alkaloid biosynthetic processes in this species. It would be of interest to see experimental studies aimed at determining the effect of soil components on these processes. In the present case, it may be a lack of, or reduction in the activity of, the oxidase(s) necessary for the dimerization process (required to form the bibenzyldihydroisoquinolines) to occur. It is also possible that the lack of dimeric alkaloids may simply reflect a concentration effect caused by the edaphic conditions. These questions should be accessible to experiment. 

The majority of trichloroethylene present on soil surfaces will volatilize to the atmosphere or leach into the subsurface. Once trichloroethylene leaches into the soil, it appears not to become chemically transformed or undergo covalent bonding with soil components. When trichloroethylene was absorbed onto kaolinite and bentonite, the nuclear magnetic resonance (NMR) spectra showed no evidence of chemical reactions (Jurkiewicz and Maciel 1995). Because trichloroethylene is a dense nonaqueous phase liquid, it can move through the imsaturated zone into the saturated zone where it can displace soil pore water (Wershaw et al. 1994). 

Jurkiewicz A, Maciel GE. 1995. Solid state C NMR studies of the interaction of acetone, carbon tetrachloride and trichloroethylene with soil components. Sci Total Environ 164 195-202. 

Hydrolysis of the isoxazole herbicide isoxaflutole rapidly produces a biologically active diketonitrile that is further degraded to products, which are partly bound to soil components and partly degraded to CO2 (Beltran et al. 2000 Lin et al. 2002 Taylor-Lovell et al. 2002) (Figure 1.24). 

Daun G, H Lenke, M Reuss, H-J Knackmuss (1998) Biological trearment of TNT-contaminated soil. 1. Anaerobic cometabolic reduction and interaction of TNT and metabolites with soil components. Environ Sci Technol 32 1956-1963. 

Polyaromatic hydrocarbons absorb strongly to humus and other soil components, rendering these contaminants difficult to remove by thermal, physical, or chemical means, and unavailable for biodegradation. To desorb polyaromatic hydrocarbons from soil, surfactant flooding processes and soil-washing processes or treatments to enhance the biodegradation of polyaromatic hydrocarbons have been considered. 

The Rhizosphere as a Site of Biochemical Interactions Among Soil Components, Plants, and Microorganisms... 

Molecular analysis of the interaction between plants, microbes, and soil components may help us understand the causal relationships of events taking plaee in the rhizosphere. Nevertheless, due to the necessity to simplify the experimental approaches, we still do not have the complete picture that takes into ae-count the relative weight of each factor. 

The first chapter defines the spatial and functional features of the rhizosphere, which make this environment the primary site of interaction between soil, plant, and microorganisms. Among the multitude of organic compounds present in the rhizosphere tho.se released by plant roots are the most important from a qualitative and quantitative point of view furthermore, the relationships with soil components of any released compound need to be considered (Chapter 2). The release of these compounds strongly depends on the physiological status of the plants and is related to the ability of plant roots to modify the rhizosphere in order to cope with unfavorable stress-reducing conditions. These aspects are dis-... 

Some agrochemicals bind strongly to the soil component as bound residues, which cannot be extracted without vigorous extraction procedures. In this case, an acidic (e.g., hydrochloric acid, sulfuric acid) or alkaline solution (e.g., sodium hydroxide, potassium hydroxide) can be used as an extraction solvent, and also heating may be effective in improving the extraction of the residues. Analytical procedures after the extraction are the same as above, but a filtration procedure may be troublesome in some of these situations. However, these procedures are rare exceptions or are needed for specific chemicals that are stable under such harsh extraction conditions. 

Bunzl K, Flessa H, Kracke W, et al. 1995. Association of fallout 239l240Pu and241 Am with various soil components in successive layers of a grassland soil. Environ Sci Technol 29 2513-2518. 

The leak detection sensitivity refers to the minimum top liner leak rate that can theoretically be detected, collected, and removed by the LDS. The leak detection time is the minimum time needed for liquids passing through the top liner to be detected, collected, and removed in the nearest down-gradient collection pipe. In the case of a composite top liner, the leak detection time refers to the period starting at the point when liquids have passed through the compacted soil component and ending at the point when they are collected in the collection pipe. 

Located wholly below the average depth of frost penetration in the area Soil component Thickness >2 ft... 

Smectite is the first secondary mineral to form upon rock weathering in the semi-arid to sub-humid tropics. Smectite clay retains most of the ions, notably Ca2+ and Mg2+, released from weathering primary silicates. Iron, present as Fe2+ in primary minerals, is preserved in the smectite crystal lattice as Fe3+. The smectites become unstable as weathering proceeds and basic cations and silica are removed by leaching. Fe3+-compounds however remain in the soil, lending it a reddish color aluminum is retained in kaolinite and A1-oxides. Leached soil components accumulate at poorly drained, lower terrain positions where they precipitate and form new smectitic clays that remain stable as long as the pH is above neutral. Additional circumstances for the dominance of clays are ... 

Exchangeable ions (EXC), sometimes including ions nonspecifically adsorbed and specifically absorbed on the surface of various soil components, such as carbonate, organic matter, Fe, Mn, Si, and Al oxides, and clay minerals. This part is controlled by adsorption-desorption processes. 

The carbonate-bound trace elements are usually extracted by NaOAc-HOAc (Tessier et al., 1979 Hickey and Kittrick, 1984 Banin et. al., 1990 and Han et al., 1992) or by using chelating agents, such as EDTA (Sposito et al., 1982 Emmerich et al., 1982 Miller and Mcfee, 1983 Chang et al., 1984 Knudtsen and O Connor, 1987 McGrath and Cegarra, 1992). Generally, EDTA lacks the required specificity and selectivity for carbonate phase extractions and tends to extract metals from a number of soil components. 

The cumulative sums of selected major and trace metals extracted by the two SSD procedures from representative arid-zone soils are shown in Fig. 4.6. As can be seen from the figure, the Rehovot procedure is stronger in attacking desired fractions, such as the carbonate bound, Mn oxide bound and organically bound fractions. Extraction of certain major elements, indicating selectivity, specificity and completeness of extraction of given soil components, was found to differ between the two procedures. Calcium and Mg were more completely extracted from the carbonate fraction in arid zone soils by the Rehovot procedure. Calcium and relevant trace elements bound in the carbonate fraction, which were not completely dissolved by the Bonn procedure at this step, were released at the following steps, such as the ERO, OM or RO fractions. 

Kingery W.L, Oppenheimer S.F., Elan F.X., Selim H.M. Adsorption/desorption hysteresis of trace metals with soil components A Dynamical systems approach. Proceedings of the Fifth International Conference on the Biogeochemistry of Trace Elements, Vienna, Austria. 1999. 

McLaren R.G., Lawson D.M., Swift R.S. Sorption and desorption of cobalt by soils and soil components. J Soil Sci 1986b 37 413 126. 

The mobility of arsenic compounds in soils is affected by sorp-tion/desorption on/from soil components or co-precipitation with metal ions. The importance of oxides (mainly Fe-oxides) in controlling the mobility and concentration of arsenic in natural environments has been studied for a long time (Livesey and Huang 1981 Frankenberger 2002 and references there in Smedley and Kinniburgh 2002). Because the elements which correlate best with arsenic in soils and sediments are iron, aluminum and manganese, the use of Fe salts (as well as Al and Mn salts) is a common practice in water treatment for the removal of arsenic. The coprecipitation of arsenic with ferric or aluminum hydroxide has been a practical and effective technique to remove this toxic element from polluted waters... 

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