Effects of humic substances on metal

Indirect Effects of Humic Substances on Metal Mobilization in Soils... 

Perdue, E. M. (1989). Effects of humic substances on metal speciation. In Aquatic Humic Substances Influence on Fate and Treatment of Pollutants, Advances in Chemistry Series, vol. 219, ed. Suffet, I. H., and MacCarthy, P., American Chemical Society, Washington, DC, 282-295. 

Perdue M. (1989) Effects of humic substances on metal speciation, Aquatic Humic Substances, Influence on Fate and Treatment of Pollutants, American Chemical Societ 281-295. 

Voelker, B.M. and Kogut, B. (2001) Interpretation of metal speciation data in coastal waters the effects of humic substances on copper binding as a test case, Marine Chemistry 74, 303-318. 

Metal mobility in soils is governed by interfacial processes, such as dissolution. The role of DOM in such processes will be determined by the nature t organic matter-surface associations. The surface complexation model pro-odes a conceptual framework for estimating the contributions of specific DOM components, particularly LMW organic ligands, to the mobilization f metals in soils. With this framework, the effects of humic substances on mineral dissolution can be interpreted to provide some insight into hu--mate-surface interactions. 

An actual contribution of humic substances to metal oxide reduction in natural systems has not been demonstrated, and there are processes such as adsorption or decomposition that could limit their effectiveness. Kostka et al. (2002a) observed that AQDS additions elicited a larger increase in Fe(III) reduction by S. oneidensis growing on ferrihydrite than smectite clay minerals. This suggests that the influence of humic substances may depend on soil or sediment mineralogy. Nevertheless, there is ample evidence to suggest that a portion of the anaerobic metabolism that was previously attributed to direct enzymatic Fe(III) and Mn(IV) reduction was actually none-nzymatic reduction by microbially reduced humic substances. 

Soil DOM comprises a wide variety of organic substances. Specific microbial or plant exudates are released as a consequence of metabolic activity of soil biota. Transformations of biogenic compounds, through partial degradation and polymerization, result in the formation of a structurally ill-defined mixture of humic substances, a term used to include both humic and fulvic acids (20, 21). Nonuniform effects of DOM components on metal mobilization may be anticipated because of the heterogeneity of their chemical structures and properties. 

Subsequent conversations with the USEPA indicated the need to determine if the presence of humic substances had any effect on the behavior of lead because humic substances can act as chelating agents for heavy metals. Therefore, an experiment was planned to evaluate the recovery of lead in the presence of humic substances. 

The presence of humic and fulvic acids in surface waters and groundwaters will have a significant influence on the transport and fate of metals, radionuclides, and organic contaminants in the environment. These natural organic acids can either transport or immobilize contaminants, depending on the environmental conditions. Humic and fulvic substances can also retard or enhance the photochemical decomposition of pesticides or toxic organics. Therefore, to be sucessfiil any remediation strategies must consider the effects of humic materials. If properly understood, this behavior can be used to manipulate pollutant solubilization and facilitate containment or cleanup of contaminated sites. 

Due to the ubiquitous occurrence of humic substances and colloids (defined as entities of Inm-lpm size) in natural waters, their specific properties, in particular their scavenging capacities towards metallic cations and also their well-established mobility (1-6), these organic and inorganic species could have important effects on the fate and mobility of these cations in natural systems. On one hand, the formation of organic complexes or pseudocolloidal species will modify the speciation (distribution of chemical species) of the cation of interest and its solubility. On the other hand, they can retard cation migration... 

The liquid phase NMR spectra comprise the first direct spectroscopic evidence differentiating phenoloxidase- and metal-catalyzed reactions from noncatalyzed nucleophilic addition reactions of aniline with humic substances. The solid state NMR spectra provide the first direct evidence for nucleophilic addition of aniline to quinone and other carbonyl groups in the organic matter of whole soil and peat. The NMR approach has potential for further investigation of the effects of reaction conditions on the incorporation of aromatic amines into naturally occurring organic matter, and for studies on how aromatic amines covalently bound to organic matter may ultimately be re-released or remineralized, either chemically or microbially. 

Wrobel, K., Sadi, B. B. M., Wrobel, K., Castillo, J. R., and Caruso, J. A., Effect of metal ions on the molecular weight distribution of humic substances derived from municipal compost ultrafiltration and size exclusion chromatography with spectrophotometric and inductively coupled plasma-MS detection. Anal. Chem., 75, 761-767, 2003. 

On the other hand, sorption/desorption experiments with copper and clay minerals have shown that true cation exchange (with BaCl2) is relatively insignificant and that the triethanolamine reagent (added to raise the pH of the solution) effects the release of additional metal compounds, which may be more appropriately designated as easily extractable phases (41). Extraction of humate phases was performed with O.IIV NaOH the same reagent was used for the determination of the concentrations of humic substances by comparison with standard humic acids (42). 

Suffet and MacCarthy [20] give the most comprehensive overview regarding appearance, chemistry and properties of humic substances. They discuss influences on waste, on drinking water preparation, on several interactions with heavy metals, on detergents and organic pollutants, reactions with light (ultraviolet radiation) and ion exchange effects. 

Vance GF, Boyd SA, Mokma DL (1985) Extraction of phenolic compounds from a Spodosol profile an evaluation of three extractants. Soil Sci 140 412-420 Vance GF, Mokma DL, Boyd SA (1986) Phenolic compounds in soils of hydrosequences and developmental sequences of Spodosols. Soil Sci Soc Am J 50 992-996 Velbel MA (1989) Effect of chemical affinity on feldspar hydrolysis rates in two natural weathering systems. Chem Geol 78 245-253 Weber JH (1988) Binding and transport of metals by humic materials. In Frimmel FH, Christman RF (eds) Humic substances and their role in the environment. Wiley, New York, pp 165-178... 

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