Humic substances modification

Perdue EM, NL Wolfe (1982) Modification of pollutant hydrolysis kinetics in the presence of humic substances. Environ Sci Technol 16 847-852. 

Figure 8,25 Classification and properties of humic substances. Reproduced with modifications from Stevenson (1983), with kind permission of Theophrastus Publishing and Proprietary Co.

A modification of the lignin theory of the formation of humic substances is the polyphenol theory, which considers the key interactions to be those between quinones, derived either from polyphenols or lignin, and amino compounds. 

The cloning of functional genes from natural microbial consortia is dependent on the high quality of the extracted and purified environmental DNA since the enzymatic modifications required during the cloning steps are sensitive to contamination by various biotic and abiotic components that are present in environmental ecosystems. For example, extraction of DNA from soils always results in coextraction of humic substances, which interfere with restriction enzyme digestion and PCR amplification and reduce transformation efficiency and DNA hybridization specificity [19 -22], Therefore, extraction methods have been developed to remove or minimize contamination of the purified DNA by humic or other interfering substances. Several protocols for the isolation of bacterial community DNA from various environmental samples have been reported in recent years. These methods are based either on re-... 

The ability to control NOM adsorption through modification of surface chemistry was demonstrated previously [20] the uptake of several model humic substances and natural organic matter isolated from surface waters decreased significantly with increasing surface acidity (as measured by NaOH neutralization). The uptake was partially restored by subsequent heat treatment of the oxidized surfaces (i.e. OX 9/70 HT650). For the wood-based carbons, the impact of surface treatment on adsorption of organic matter was surprisingly small or absent. Overall, the reactivity of carbon surfaces to DOM uptake depended on the raw material type, activation conditions and surface treatment. 

A useful procedure for the isolation of humic substances from groundwater is that of Thurman and Malcolm (1981) with the following modifications. Hydrochloric acid should be added immediately to the water sample to prevent the precipitation of iron hydroxide, and the sample should be evacuated with a vacuum pump to remove hydrogen sulfide. If the sulfide is not removed, it can react to form both elemental sulfur and polysulfides that adsorb onto and clog the XAD resin (Leenheer and Noyes, in press Thurman, 1979). 

The assignment of infrared absorption bands of humic substances is facilitated by chemical modification of the material. In particular, the assignment of the 3400 cm band to OH stretching vibrations has been substantiated by methylation of OH groups (Wagner and Stevenson, 1965). 

A more simple treatment is the pH correction, very often used for regulation compliance (the pH value of the treated effluent must be between 5.5 and 8.5). A pH modification can also be used for metallic compound precipitation usually as hydroxide forms, in alkaline conditions, or for humic substances removal, in acidic conditions. The effect of this last treatment can be shown for landfill leachates treatment in Chapter 10. 

Chlorinated organic compounds are formed when chlorine used in bleaching the pulp reacts with phenols of the wood and humic substances during the pulping step. These pollutants are discharged with the effluents into the aquatic environment. It has been found that some of these effluents are lethal even at concentrations as low as 3.2% of the effluent. Chronic effects, including gross deformities, embryo and larval mortalities, behavioral modifications, and reproductive abnormalities, have been documented even at very low concentrations of effluent. 

FIGURE 10.2 Separation and fractionation procedure according to the IHSS (Swift 1996) with some modifications from Hayes and coworkers. (From Clapp, C. E. and Hayes, M. H. B., Soil Science, 164, no. 12, 899—913, 1999 Hayes, M. H. B. and Malcolm, R. L., Humic Substances and Chemical Contaminants, Soil Science Society of America, Madison, WI, 2001.)... 

The term humic substance is used here as a generic expression to include HA and FA and humin (Table 3). It is now generally agreed that humic substances are the products of chemical and biological degradation and modification of plant and animal remains, and the activities of soil microbes. However, little is known of the chemistry of the major reactions which are essential for the production of humic substances. 

Hofrichter M, Fakoussa R M (2001), Microbial degradation and modification of coal , in Hofiichter M, Steinbiichel A, Biopolymers 1, Lignin, Humic Substances and Coal, Weinheim, Wiley-VCH, 393-120. 

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