SORBED ORGANICS

Bioavailability issues have been reviewed previously (Mihelcic etal. 1993 Boesten 1993 Baveye and Bladon 1999 Ehlers and Luthy 2003). In this review, we discuss specifically the bioavailability of soil- or sediment-sorbed organic contaminants to pollutant-degrading bacteria. Direct uptake of sorbed contaminants is perhaps the most controversial and least understood process. The definition of bioavailability given by Alexander (2000) will be used in this review. The term bioaccessibility encompasses what is immediately available plus that which may become available, whereas bioavailability refers to what is available immediately. 

Bioavailability of soil-sorbed organic chemicals depends on a variety of physicochemical factors as well as the characteristics of microorganisms involved. Although many studies have provided insight to our understanding of the bioavailability issue, simple correlations have not been found between bioavailability and physicochemical properties of sorbed chemicals or sorbents, nor microbial characteristics. 

Bioavailability is also influenced by certain, albeit poorly understood, characteristics of bacteria. To degrade soil-sorbed molecules, bacteria must either use sorbed molecule directly or facilitate desorption in some manner. Mechanisms underlying the apparent availability of sorbed chemicals are complex due to the divergent properties of chemicals considered, the resultant sorption/desorption mechanisms, the metabolic diversity of microorganisms, and the heterogeneity of soils. Several microbial-based mechanisms have been proposed for the access of soil-sorbed organic chemicals (i) production of bio surfactants (Desai and Banat 1997 Alexander 1999) ... 

A solid phase, as discussed in detail in Chap. 2, is composed of varying amounts of mineral and organic matter which influence the crumb structure and the binding capacity, by the association of clay minerals with organic matter of the solid. The ability of a solid phase to sorb organic pollutants is also influenced by variable system conditions and differing environmental conditions. 

Comelissen, G. Rigterink, H. ten Hulscher, D.E.M. Vrind, B.A. Van Noort, P.C.M. 2001, A simple Tenax extraction method to determine the availability of sediment-sorbed organic compounds. 

Researchers at Lehigh University have investigated the ability of ground tire rubber to sorb organic compounds such as benzene, toluene, ethylbenzene, and xylene (BTEX) to determine the feasibility of using the rubber as the sorbent media in reactive permeable barrier systems. Thus far, no field-scale work has been performed on this technology. Both batch and packed-bed column tests have been conducted. All information is from the researchers and has not been independently verified. 

In order to evaluate the ability of natural organic materials to sorb organic pollutants, it is useful to define an organic carbon normalized sorption coefficient ... 

The accumulation of sorbed organic ions relative to ion concentrations in the bulk solution is due to a free energy increment ... 

Weber, J.B., Best, J. A. Gonese, J. U. (1993). Bioavailability and bioactivity of sorbed organic chemicals. In Sorption and Degradation of Pesticides and Organic Chemicals in Soil, ed- D.M. Linn, T. H. Carski, M. L. Brusseau, F-H. Chang, pp. 153-96. Madison, WI Soil Science Society of America, American Society of Agronomy. 

It must not, however, be forgotten that conventional techniques (e.g., 13C Fourier transform NMR) can be applied to certain solids of catalytic significance, such as sheet silicates since in many of these systems rapid motion of intercalated or otherwise sorbed organic species secures sharp absorption lines which provide much information about the individual atomic environments. Organic species attached to high surface area solids (such as zeolites, silica, alumina, magnesia, as well as other oxides and their mixtures) are specific examples (6). 

Zeolites display a number of interesting physical and chemical properties. The three classes of phenomena of greatest practical importance are the ability to sorb organic and inorganic substances, to act as cation exchangers, and to catalyze a wide variety of reactions. The most important aspects of these are described below. 

A very interesting development was the discovery (101) that the 29Si spectra of silicalite are highly sensitive to even small amounts of sorbed organics such as ethanol, 1-propanol, n-decane, and especially benzene (Fig. 29). The transformation of the spectra is accompanied by a distortion of the silicate framework, as demonstrated by X-ray diffractometry (102). 

Fig. 29. 29Si MAS NMR spectra (101) at 39.76 MHz of silicalite (Si/Al) > 4400) containing sorbed organic molecules. (A), parent material (B), containing ethanol (C), containing 1-propanol (D), containing n-decane (E), containing benzene.

Sedimentary rocks with the highest arsenic concentrations largely consist of materials that readily sorb or contain arsenic, such as organic matter, iron (oxy)(hydr)oxides, clay minerals, and sulfide compounds. Arsenian pyrite and arsenic-sorbing organic matter are especially common in coals and shales. Ironstones and iron formations are mainly composed of hematite and other iron (oxy)(hydr)oxides that readily sorb or coprecipitate arsenic. Iron compounds also occur as cements in some sandstones. Although almost any type of sedimentary rock could contain arsenic-rich minerals precipitated by subsurface fluids (Section 3.6.4), many sandstones and carbonates consist almost entirely of minerals that by themselves retain very little arsenic namely, quartz in sandstones and dolomite and calcite in limestones. 

A hydrophobic bonding mechanism is the result of an overall entropy gain of the system due to the displacement of water molecules from the clay surface by sorbed organic compounds. The contributions of this mechanism will be more pronounced in the adsorption of high-molecular-weight organic matter (Parfitt and Greenland, 1970 Mortland, 1970). 

Carbonaceous aerosols in the atmosphere are complex in nature and are found in both coarse particles (> about 2.5 pm) and fine particles (< about 2.5 pm). Sources of carbon-containing particles are varied and include resuspended soil particles, pollen, plant waxes, etc. in the coarse fraction, and soot particles, sorbed organics including PAHs, and secondary aerosols resulting from... 

Kalman, D., Dills, R., Perera, C., and De Walle, F. (1980). On-column cryogenic trapping of sorbed organics for determination by capillary gas chromatography. Anal. Chem. 52, 1993-1994. 

Thorbjarnarson KW, Mackay DM (1994) A forced gradient experiment on solute transport in the Borden aquifer 3. Nonequilibrium transport of the sorbing organic compounds. Water Resour Res 30 401-419... 

If exposed to organics, treatment of the membrane with propene may be a good solution. Jones and Koros [82] found propene to be very effective in removing sorbed organics. In some cases the flux was completely restored—this was also confirmed by Hagg et al. [83]. 

Soil Organic Matter. A variety of soils and sediments sorb organic compounds in patterns that can be approximated by linear isotherm models, at least over relatively narrow (e.g., 1 decade) concentration ranges. Such isotherms are generally, although often imprecisely, expressed in terms of a partitioning coefficient, fy such that... 

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