Fulvic acid properties

Plaza, C.,Senesi,N., Polo, A.,Brunetti, G., Garcla-Gil, J. C., and D Orazio, V. (2003).Soil fulvic acid properties as a means to assess the use of pig slurry amendment. Soil Till. Res. 74, 179-190. 

The Table shows a great spread in Kd-values even at the same location. This is due to the fact that the environmental conditions influence the partition of plutonium species between different valency states and complexes. For the different actinides, it is found that the Kd-values under otherwise identical conditions (e.g. for the uptake of plutonium on geologic materials or in organisms) decrease in the order Pu>Am>U>Np (15). Because neptunium is usually pentavalent, uranium hexavalent and americium trivalent, while plutonium in natural systems is mainly tetravalent, it is clear from the actinide homologue properties that the oxidation state of plutonium will affect the observed Kd-value. The oxidation state of plutonium depends on the redox potential (Eh-value) of the ground water and its content of oxidants or reductants. It is also found that natural ligands like C032- and fulvic acids, which complex plutonium (see next section), also influence the Kd-value. 

Another compartmental partitioning issue of major consequence for pesticides is the dissolved versus adsorbed fraction in an aqueous environment. Carter and Suffet (16) present measurements of binding of pesticides to dissolved fulvic acids that-will provide inputs to compartment models. Data from laboratory measurements used in compartment models can often bypass costly field experiments in the screening stage. Thomas, Spillner and Takahashi (1 7) have related the soil mobility of alachlor, butylate and metachlor to physicochemical properties of these compounds. 

Yu H, Xi B, Ma W, Li D, He X. Fluorescence spectroscopic properties of dissolved fulvic acids from salined flavo-aquic soils around Wuliangsuhai in Hetao Irrigation District, China. Soil Sci. Soc. Am. J. 2011 75 1385-1393. 

Humic and fulvic acids contain various types of phenolic and carboxylic functional (hydrophilic) groups as well as aromatic and aliphatic moieties which import hydro-phobic properties to these substances. Fig. 4.12 gives a schematic idea on the composition of these substances. We refer to the book of Thurman (1985) and Aiken et al. (1985) for a description of the various properties of humic and fulvic acids in soils and waters and the book by Buffle (1988) for the coordinating properties of humus and humic acids. 

If one wants to understand why such changes occur, one can look at a few of the basic equilibrium properties of such complexes. Figure 1 illustrates the trends which occur when a sample is titrated with copper, monitoring three different parameters. The black dots indicate the relative amount of bound copper as indicated by free copper ions sensed with an ion-selective electrode (Xc of left ordinate). The triangles represent the change of the absorbance of the solution at 465 nm (right ordinate). The curve with the open circles is the relative quenching of the fulvic acid fluorescence (Q of left ordinate). We see that we are able to probe several different types of sites with different types of probes for this multidentate system. 

Schnitzer and Hansen (59) have studied the sequestering properties of fulvic acid at low pH and observed the following order ... 

Buffle, 3., Greter, F.L. and Haerdi, W., 1977. Measurement of complexation properties of humic and fulvic acids in natural waters with lead and copper ion selective electrodes. Anal. Chem., 49 216-222. 

The fluorescence properties of two fulvic acids, one derived from the soil and the other from river water, were studied. The maximum emission intensity occurred at 445-450 nm upon excitation at 350 nm, and the intensity varied with pH, reaching a maximum at pH 5.0 and decreasing rapidly as the pH dropped below 4. Neither oxygen nor electrolyte concentration affected the fluorescence of the fulvic acid derived from the soil. Complexes of fulvic acid with copper, lead, cobalt, nickel and manganese were examined and it was found that bound copper II ions quench fulvic acid fluorescence. Ion-selective electrode potentiometry was used to demonstrate the close relationship between fluorescence quenching and fulvic acid complexation of cupric ions. It is suggested that fluorescence and ion-selective electrode analysis may not be measuring the same complexation phenomenon in the cases of nickel and cobalt complexes with fulvic acid. 

To maintain a focus on the use of tracers in DOM fractions, this chapter will present only brief descriptions of studies of bulk DOM properties, and will focus primarily on the use of trace moieties from the fulvic acid fraction in freshwater aquatic environments. In addition to being a major DOM fraction, fulvic acid is biogeochemically reactive in natural waters (see Maranger and Pullin, Chapter 8 Chin, Chapter 7 Moran and Covert, Chapter 10). Furthermore, current fractionation methods allow for relatively straightforward isolation of small quantities of fulvic acid from small volume filtered water samples (100-200 mL) in a reproducible manner, as well as for isolation of larger preparative quantities of material. We present examples to illustrate the use of particular trace moieties but do not present a comprehensive review of each trace moiety. 

We found consistent differences in the fluorescence properties of fulvic acids from streams where fulvic acids are terrestrially derived and from lakes where fulvic acids are microbially derived (McKnight et al., 2001). The upper maximum in microbially derived samples is more sharply defined and... 

TABLE III Differences in Chemical Properties of Suwannee River Fulvic Acid Sorbed onto Iron Oxide (Sorbable) and Suwannee River Fulvic Acid Remaining in Solution (Nonsorbable)... 

Leenheer, J. A., D. M. McKnight, E. M. Thurman, and P. MacCarthy. 1989. Structural components and proposed structural models of fulvic acid from the Suwannee River. In Humic Substances in the Suwannee River, Georgia Interactions, Properties, and Proposed Structures. U.S. Geological Survey Open-File Report 87-557, pp. 335-359. 

McKnight, D. M., E. W. Boyer, P. Doran, P. K. Westerhoff, T. Kulbe, and D. T. Andersen. 2001. Spectrofluorometric characterization of aquatic fulvic acid for determination of precursor organic material and general structural properties. Limology and Oceanography 46 38. 

Plaza, C., Senesi, N., Polo, A., and Brunetti, G. (2005b). Acid-base properties of humic and fulvic acids formed during composting by the NICA-Donnan model. Environ. Sci. Technol. 39, 7141-7146. 

Sposito, G., Holtzclaw, K. M., and Baham, J. (1976). Analytical properties of the soluble, metal-complexing fractions in sludge-soil mixtures II. Comparative structural chemistry of fulvic acid. Soil Sci. Soc. Am. J. 40, 691-697. 

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