Humic materials in soils

Gonzales and Laird145 have shown that smectites abiotically catalyze dehydration of glucose to form furfural under conditions similar to those found in soils. Four smectite clay minerals were used (saturated with Na, Ca, Fe, or Al), and the formation of HMF and furfural was detected by high-pressure liquid chromatography. The polymerization of furfural may thus be a pathway to the formation of new humic materials in soils. 

Sposito, G. (1986), "Sorption of Trace Metals by Humic Materials in Soils and Natural Waters", CRC Crit. Rev. Environ. Control 16, 193-229. 

The biovailability of an element in the soil is the result of a competition between surface complexation at the plant root system, at various soil solid phases, and that remaining in solution. Organic and humic materials in soils act as ligands and the resulting complexes can be important in the movement of metal ions (Lindsay, 1974). At present there is little information on the relationship between concentration of the complexed species and their uptake rate by plants though some general evidence sug-... 

Sposito, G. 1985. Sorption of trace metals by humic materials in soils and natural waters. CRC... 

Figure 9 Possible pathways for formation of humic material in soil from inputs of plant residues...

The first natural-abundance N NMR spectrum on humic material was obtained by the solid-state CPMAS technique on a peat having a nitrogen content of 4% by Preston et al.(53). After systematic determination of important N NMR spectral parameters, it was possible to obtain solid-state N NMR spectra of humic material in soil and sediments at natural N levels(60-62) with an acceptable signal-to-noise ratio. Recently solid-state N NMR spectroscopy was extended to the investigation of the nitrogen functionality in coals.(63)... 

Most of the humic materials in soils, as well as sediments, occurs in insoluble forms. The ways in which humic substances are bound include the following ... 

First, we have to assure that the humic substances investigated are insoluble, This does not seem to be a severe limitation because most humic materials in soils or sediments occur in insoluble forms (Stevenson, 1985) either as macromolecular complexes or in combination with clay materials. A partial solubility of the humic material may, however, occur if the pH of the solution for the sorption experiment is selected too high. 

Humic materials in soil strongly sorb many solutes in soil water and have a particular affinity for heavy polyvalent cations. Soil humic substances may contain levels of uranium more than 10" times that of the water with which they are in equilibrium. Thus, water becomes depleted of its cations (or purified) in passing through humic-rich soils. Humic substances in soils also have a strong affinity for organic... 

Many of the PCBs found in the aquatic environment (e.g., in lakes and in the Arctic and Antarctic) have migrated via atmospheric dispersion of vapors [404-410]. Vaporization of PCBs from soil decreases as the amount of humic material in the solid phase increases due to mainly partitioning processes [381-390]. Griffin and Chian [363] note that vaporization of PCBs from suspensions of solids or humic acids is reduced by the presence of these materials. 

Some allelochemicals have been shown to be bound by the humic material in the soil and presumably inactivated (90). When known amounts of tannic acid were added to a prairie soil that contained no tannic acid, a minimum of WQ ppm had to be added before any could be recovered immediately. It is noteworthy, therefore, that as small a concentration as 30 ppm added to the same soil reduced the nodule number of heavily inoculated legumes growing in the soil. Obviously, some of the bound tannic acid remained biologically active (91). 

Analytical methods used for determining DNOC in environmental samples are given in Table 6-2. Most of the methods for products, waters, soils, and sludges rely on extraction of DNOC from an acidified matrix acidification minimizes dissociation of the phenolic hydrogen and thus facilitates extraction into an organic solvent or adsorption onto a solid phase extraction medium. The influence of pH on the adsorption of DNOC to humic materials in coal waste waters has been studied (Porschmann and Stottmeister 1993) and significant adsorption was found to occur at pH 7 but not... 

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