Phenolics from soils

Preliminary laboratory data demonstrate the feasibility of removing Pb, Cr, Cd, Ni, Cu, Zn, As, TCE, BTEX compounds, and phenol from soils (clays and sandy clayey deposits, and dredged sediments) using EO technology. It has been demonstrated that 75 to 95% of Pb can be removed across the cell, in which a significant amount of the removed Pb can be electroplated at the cathode. 

Experiment I. Extraction of phenolics from soil samples... 

Lopez-Avila et al. [7] used microwave assisted extraction to assist the extraction of phenols from soils. 

To overcome some of the difficulties, Crespin et al. [113] developed a semiautomatic module for the direct continuous extraction and preconcentration of phenols from soils. 

It can be noted that, in most cases, lower recoveries are obtained when shake-flask extraction is used to remove phenols from soil when compared to Celite (an inert siliceous matrix). This effect is most pronounced with 1-naphthol. 

PAHs can be eluted as a separate band although they may still coelute with chlorinated aromatics, pesticides, and nitroaromatics, thus necessitating another cleanup step prior to analysis. Another strategy is to separate the organic acids and phenols from soil/sediment extracts by performing a liquid-liquid extraction with 10 N NaOH. ° The solvent extract is shaken in a separatory funnel with three aliquots of concentrated NaOH. The combined extracts containing the acids and phenols is discarded while the extract, in DCM, is dried and concentrated for GC analysis or solvent exchanged for another analysis method. 

Popov K, Kolosov A, Yachmenev VG, Shabanova N, Artemyeva A, Frid A, Kogut B, Vesnovskii S, Sukharenko V. (2001). A laboratory-scale study of applied voltage and chelating agent on the electrokinetic separation of phenol from soil. Separation Science and Technology 36(13) 2971-2982. 

Several facts have emerged from our studies with 2,7-DCDD and 2,3,7,8-TCDD. They are not biosynthesized by condensation of chloro-phenols in soils, and they are not photoproducts of 2,4-dichlorophenol. They do not leach into the soil profile and consequently pose no threat to groundwater, and they are not taken up by plants from minute residues likely to occur in soils. Photodecomposition is insignificant on dry soil surfaces but is probably important in water. Dichlorodibenzo-p-dioxin is lost by volatilization, but TCDD is probably involatile. These compounds are not translocated within the plant from foliar application, and they are degraded in the soil. 

The uptake and biotransformation of benzene from soil and the atmosphere has been studied in a nnmber of plants. It was shown that in leaves of spinach Spinacia oleraced) the label in -benzene was fonnd in mnconic, fnmaric, snccinic, malic, and oxalic acids, as well as in specific amino acids, and that an enzyme preparation in the presence of NADH or NADPH prodnced phenol (Ugrekhelidze et al. 1997). 

A strain that is able to degrade 2-chloro-A-isopropylacetanilide was successful in removing this from soil (Martin et al. 1995). It is notable that this strain was unable to grow with either aniline or phenol. 

Although there is no doubt as to the importance of mycorrhizae in nutrient absorption, reviews on ion uptake have generally not considered it. Hatling et al. (143) made this same point more than 10 years ago. In addition, although phenolic acids inhibit phosphate (144, 145) and potassium (146) uptake, no work has examined the effects of these compounds on nutrient absorption of mycorrhizal associations. Since soil microorganisms produce the bulk of the volatile compounds emitted from soil, which are known to inhibit or stimulate fungal development (147-148), this group of compounds from microbial sources should receive more attention. 

Supercritical extractions such as that illustrated in Procedure 12.3 have been used to extract phenols, organochlorine, organophosphate compounds, and amines from soil [9,10,12],... 

Johnson and Van Emon [57] have described a quantitative enzyme based immunoassay procedure for the determination of polychlorinated biphenyls in soils and sediments and compared the results with those obtained by a gas chromatographic method. The soil is extracted with methanol, or Soxhlet extracted or extracted with a supercritical fluid. In the case of the latter two extractants good agreement was obtained between immunoassay and gas chromatographic methods. Spiking recoveries from soil achieved ranged from 104% (Aroclor 1248) to 107% (Aroclor 1242). Detection limits were 9pg kg-1 (Aroclor 1245) and 10.5pg kg-1 (Aroclor 1242). Chlorinated anisoles, benzenes or phenols did not interfere. 

It is also important to understand that most allelopathic effects apparently result from the combined actions of several allelochemicals, often with each below a threshold concentration for impact. In allelopathic situations which implicate phenolic acids, soil concentrations have ranged from below 10 to above 1000 ppm for each compound. The lower end of the spectrum is below a concentration required for an effect in current bioassays. Additive and synergistic effects have been demonstrated, however, for combinations of cinnamic acids (102), benzoic acids (103), benzoic and cinnamic acids (10 ). and -hydroxybenzaldehyde with coumarin (105). It appears that such combined interactions may be very important under field conditions. 

Irrespective of the sources of phenolic compounds in soil, adsorption and desorption from soil colloids will determine their solution-phase concentration. Both processes are described by the same mathematical models, but they are not necessarily completely reversible. Complete reversibility refers to singular adsorption-desorption, an equilibrium in which the adsorbate is fully desorbed, with release as easy as retention. In non-singular adsorption-desorption equilibria, the release of the adsorbate may involve a different mechanism requiring a higher activation energy, resulting in different reaction kinetics and desorption coefficients. This phenomenon is commonly observed with pesticides (41, 42). An acute need exists for experimental data on the adsorption, desorption, and equilibria for phenolic compounds to properly assess their environmental chemistry in soil. 

The Extraksol process can extract organic contaminants such as oils and greases, polynuclear aromatic hydrocarbons (PAHs), pentachlorophenols (PCPs), and phenols from a variety of solid matrices. The Extraksol process can extract polychlorinated biphenyls (PCBs) from clay-bearing soil, sand, and FuUer s earth. Extraksol has successfully treated various media such as activated carbons, refinery sludges, and wood treatment sludges. 

IT thermal desorption has been used for several years to demonstrate removal of chlorinated phenols, pesticides, polycyclic aromatic hydrocarbons (PAHs), dioxins, polychlorinated biphenyls (PCBs), solvents and mercury from soils and sludges. 

Supercritical C02 has also been tested as a solvent for the removal of organic contaminants from soil. At 60°C and 41.4 MPa (6,000 psi), more than 95% of contaminants, such as diesel fuel and polychlorinated biphenyls (PCBs), may be removed from soil samples (77). Supercritical C02 can also extract from soil the following hydrocarbons, polyaromatic hydrocarbons, chlorinated hydrocarbons, phenols, chlorinated phenols, and many pesticides (qv) and herbicides (qv). Sometimes a cosolvent is required for extracting the more polar contaminants (78). 

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