Soil humic components

The Emergence of Procedures for the Isolation of Soil Humic Components 4... 

EMERGENCE OF CONCEPTS OF COMPOSITIONS AND STRUCTURES OF SOIL HUMIC COMPONENTS... 

Pre- and Some Early 20th-Century Concepts of Soil Humic Components and Functions... 

Schnitzer, M. (1965b). The application of infrared spectroscopy to investigations on soil humic components. Can. Spec. 10, 121-127. 

Particularly polar contaminants may associate with polymeric humic components of soil, water, and sediment. Their biodegradation then depends on the degree to which these processes are reversible and the contaminants become accessible to microorganisms (bioavailable). This is especially significant after weathering (aging), even for nonpolar compounds. 

Shand CA, Cheshire MV, Bedrock CN, Chapman PJ, Fraser AR, Chudek JA. Solid-phase P-13 NMR spectra of peat and mineral soils, humic acids and soil solution components influence of iron and manganese. Plant Soil 1999 214 153-163. 

Treatment of PCBs in soil may require more sodium borohydride than required for pure PCBs due to residual water and reducible humic components that might be present and consume sodium borohydride. 

A problem for both humic- and yellow substances is that for these groups of experimentally defined components of different sources, each analysis will be ambiguous in terms of relative composition and molecular weight distribution. Additionally it appears that almost every scientist working in this field has developed his own extraction procedure (Weber and Wilson, 1975 Mantoura and Riley, 1975 a Schnitzer, 1976 Stuermer and Harvey, 1977). Different extraction times and -procedures result in different compositions of the organic constituents (Laane and Kramer, 1984). Soil humic-and fulvic acids, often used for studies on the interaction with trace elements, and those derived from water have certainly not the same composition and contain not the same distribution of functional groups. Therefore, results should be compared with care (Buffle, 1980 Buffle et al., 1984). 

Though plants are the predominant source of most of this material, microbial inputs are important as well (Cheshire, 1977). Carbohydrate extracts from soils and sediments probably contain only a small fraction of the total carbohydrate concentration since much of the carbohydrate content appears to be polysaccharides bound to the humic components (Lowe, 1978), and probably to clay minerals as well. Its presence is recognized by the release of simpler sugars upon hydrolysis of the sample (Greenland and Oades, 1975 Lowe, 1978). Isolated polysaccharide fractions are generally polydisperse mixtures. 

Haumaier, L., and Zech, W. (1995). Black carbon—Possible source of highly aromatic components of soil humic acids. Org. Geochem. 23,191-196. 

In its inorganic form, P is a nutrient showing low solubility and mobility in the soil, because it easily reacts with the soil mineral components (clay, iron and aluminum oxides, and carbonates) (Stevenson, 1986). The P content in humic substances ranges from 0.1% to 1.0% and is particularly abundant in humic acids. By using 31P NMR, it was shown that different forms of P can be associated with humic fractions... 

Various separation methods have been used to isolate, fractionate, and characterize humic materials. Originally it was fractionation, based on solubility differences of humic components in diluted alkalis and acids, which laid the ground work for the first classifications of humic substances (HS) in the 19th century (Mulder, 1861 Sprengel, 1837) and provided for operational definition of HS (Kononova, 1966). And now, alkali extraction is the method of choice for isolating HS from solid humus-containing substrates like soil, peat, coal, and so on (Swift, 1996), while hydrophobic resins (e.g., Amberlite XAD resins) are typically used to extract HS dissolved in natural waters (Aiken, 1985). Initial research on HS began with the used simple separation methods to prove, examine, and define characteristics of components of humic matter (Oden, 1919).Today, however, advances in HS research require ever more sophisticated techniques of separation combined with structural analysis (Orlov, 1990 Stevenson, 1994). 

Pyrolysis of humic materials and of its components has been done for numerous purposes. One such purpose is structure elucidation. Also, as humic substances have more components that are of different origin (cellulose, lignin, plant cuticular materials), pyrolysis has been used to infer the source of each humic component and to assess its resistance to degradation in time [5]. Also, characterization of different types of soils has been done using pyrolysis studies [6,7]. 

The aromatic acids released from different HA upon pyrolysis in the presence of TMAH probably represent original components of the HA structure released by the thermolytic action of TMAH (10,12,16,17). This observation is supported by the TMAH thermochemolysis data of Hatcher et al. (23) and Hatcher and Clifford (16) for a volcanic soil humic acid. In fact, the C-NMR spectrum of this particular HA (shown in Figure 4) clearly indicates that it is composed of only aromatic and carboxyl carbons. Conventional pyrolysis of these HA produced trace quantities of volatile products without the release of any significant compounds while pyrolysis in the presence of TMAH yielded mainly benzenecarboxylic acid methyl esters (Figure 5), in accordance with the NMR data. 

NMR Spectra of Soil Humic Acid Reacted with Aniline. ACOUSTIC NMR spectra of the soil humic acid reacted with the labelled aniline in the presence and absence of peroxidase and bimessite are shown in Figure 8. As discussed previously, the sharp peak at 315 ppm in the spectrum of the noncatalyzed reaction appears to represent the reaction product of aniline with a contaminant or pure component in the humic acid sample (9). Vertical expansion of the spectrum revealed a broad, low intensity imine peak underlying the sharp contaminant peak. This underlying imine peak is more clearly visible in the solid state spectrum of the sample (Figure 9B), where the sharp contaminant peak is broadened out presumably as a result of chemical shift anisotropy. Imine nitrogens were also... 

When oxide minerals are exposed to a mixture of organic substances, such as soil DOM, the composition of the mixture will determine the extent to which oxide dissolution is enhanced. Thus, to evaluate the role of soil DOM in the dissolution of soil minerals, the effectiveness of individual DOM components in promoting dissolution and the interactions of various components must be considered. The following discussion will examine the possible roles of two types of soil DOM components, humic substances and LMW organic... 

Humic substances in soil have properties similar to those found in other natural systems. Accordingly, results obtained by the soil scientist on the nature, origin, and reactions of these complex substances are of considerable interest to researchers in several disciplines of science. In this chapter emphasis is given to historical aspects of research on soil humic substances, to the interactions of humic and fulvic acids with soil mineral components, and to the participation of humic substances in geochemical processes. 

---