Humic substances extraction

Figure 1 Proposed role of humic substances on iron nutrition of plants possessing dif fereni strategies for iron acquisition. WEHS, water-extractable humic substances, as described in the text.

S. Cesco, V. Rdmheld, Z. Varanini, and R. Pinton, Solubilization of iron by a water extractable humic substances fraction. J. Plant Nutr. Soil Sci. 763 285 (2000). 

R. Pinton, S. Cesco, M. De Nobili, S. Santi, and Z. Varanini, Water- and pyrophosphate-extractable humic substances fractions as a source of iron for Fe-dettcient cucumber plants. Biol. Fert. Soils 26 23 (1998). 

R. Pinton, S. Cesco, G. lacolettig, S. Astolfi, and Z. Varanini, Modulation of NO", uptake by water-extractable humic substances involvement of root plasma membrane H -ATPase. Plant Soil 215 155 (1999). 

Supercritical fluid extraction (SFE) is generally used for the extraction of selected analytes from solid sample matrices, but applications have been reported for aqueous samples. In one study, recoveries of 87-100% were obtained for simazine, propazine, and trietazine at the 0.05 ug mL concentration level using methanol-modified CO2 (10%, v/v) to extract the analytes, previously preconcentrated on a C-18 Empore extraction disk. The analysis was performed using LC/UV detection. Freeze-dried water samples were subjected to SFE for atrazine and simazine, and the optimum recoveries were obtained using the mildest conditions studied (50 °C, 20 MPa, and 30 mL of CO2). In some cases when using LEE and LC analysis, co-extracted humic substances created interference for the more polar metabolites when compared with SFE for the preparation of the same water sample. ... 

R. (2000) Solubilization of iron by water-extractable humic substances. J. Plant Nutr. SoilSd. 163 285-290 Chabaux, F. Cohen, A.S. O Nions, R.K. ... 

Also, Schmidt et al. (2005) found a significant increase in root hair density by working with Arabidopsis thaliana, which were treated with water extractable humic substances (WEHS), suggesting that these substances induce a nutrient acquisition response that favors the uptake of nutrients via an increase in the absorptive surface area. Furthermore, a phenotypical analysis of an array of mutants harbouring defects in root epidermal patterning revealed that root hair density of the ttg and gl2 mutants, defective in cell specification, was significantly modified, indicating an effect at/or downstream of the determination of the cells. 

Pinton, R., Cesco, S., Iacoletti, G, Astolfi, S., and Varanini, Z. (1999a). Modulation of NO3 uptake by water-extractable humic substances Involvement of root plasma membrane H+ATPase. Plant Soil 215,155-161. 

Schmidt, W., Santi, S., Pinton, R., and Varanini, Z. (2007). Water-extractable humic substances alter root development and epidermal cell pattern in Arabidopsis. Plant Soil 300,... 

The high production volume chemical, 4-chloro-2-methylphenol, XVI was photolysed in distilled and natural waters and aqueous solutions of soil-extracted humic substances (Ranker, Spain) under various irradiation conditions with monochromatic light at 280 nm, using polychromatic lamps emitting between 300 and 450 nm, and in natural sunlight (June, Clermont-Ferrand, France) [78,79]. 

IJi ammonia 10 extract 1 week extracts "humic substances" ... 

The surface activity of the different stream and foam humic-substance fractions and its relation to carboxyl content are strong evidence for the importance of the carboxyl groups in controlling the surface activity of the humic substances. Furthermore, the comparable surface-active behavior of the foam-extract fractions to raw foam is indicative that foam-extract humic substances are the main foaming agent in raw foam, and a chemical characterization of these fractions may reveal the chemical nature of the foaming constituents. 

Table Vin. Percentage contributions by weight of different classes of fatty acids bound to phospholipids in Suwannee River samples of raw foam and stream, foam, and foam-extract humic substances.

Methods for extracting humic substances must take into account the various ways in which organic matter is bound. Free forms of humic and fulvic acids can be recovered by procedures used to displace the soil solution, as well as by extraction with neutral salt solutions or dilute mineral acids. The usual procedure for recovering humic material bound to polyvalent cations is... 

In addition to direct extraction of humic substances, the amount of humic substances has been estimated by subtracting the amount of biochemicals (sum of lipids, amino acids or proteins, and carbohydrates) from the total organic matter in the sediments (Kemp and Johnston, 1979). In this chapter, this difference is called nonbiochemicals, although no doubt there is much overlap between nonbiochemicals and extracted humic substances. As shown in Table 2, nonbiochemicals amount to 42-58% of the total organic matter in two Japanese lake sediments, but in the Great Lake (North America) sediments nonbiochemicals amount to 70-79% of the total organic matter on average. The latter values are close to those observed for marine sediments (Ishiwatari, 1979). 

Povoledo et al. (1975) also observed absorption bands at 410 and 670 nm for lake humic acids extracted without prior organic solvent extraction. They concluded that the pigments responsible for these bands were chlorophyll derivatives, notably pheophytin a, and reported the approximate content in humic acid from a Canadian lake sediment was 0. %. They reported that other pigments (e.g., carotenoids) were also present in lake humic acids without prior organic solvent extraction. Bourbonniere and Meyers (1978) extracted humic substances from Lake Huron surficial sediment without prior organic solvent extraction and measured visible spectra in 0.05N NaHC03 solution (pH 7.3-8.7) which gave 465/ 665 values of 3.92 for humic acid and 10.66 for fulvic acids. 

A portion of these biochemical compounds may be associated with the extracted humic substances. However, as already described, the humin which had been hydrolyzed by 6N HCl at 110°C for 24 hours gave essentially the same oxidative (KMn04) degradation products (aliphatic C4-C14 a,co-dicarboxylic acids as major products) as untreated humin. Moreover, stepwise (eight steps) oxidative (KMn04) degradation of humin produced similar degradation products (aliphatic Cs-C 8 monocarboxylic and C5-C16 a,co-dicarboxylic acids and small amounts of benzenecarboxylic acid Machihara and Ishiwatari, 1980). These facts indicate that the major part of humin forms aliphatic structures with biochemical compounds distributed uniformly in the humin matrix. These compounds are firmly linked within the humin matrix by unknown bonds. 

Ishiwatari (1977) isolated humic acids and humin from samples at various depths (11-130 m) of Lake Biwa sediment. As shown in Table 9, a small amount of humic acid was extracted from sediments of 11 m depth, but no humic acid was obtained from sediments in deeper layers (45-130 m) although alkali extracts were yellow-colored. Humin isolated from sediment samples increased with depth from 6.2% of the total organic matter to 64%, and at 130 m in depth accounted for 80% of the nonbiochemicals. Ishiwatari and Kawamura (1981) again measured approximate amounts of alkali-ex-traetable humie substances in the long sediment core sample of Lake Biwa by colorimetry (at 400 nm). The ratios of alkali-extractable humic substances to the total organic matter decreased gradually with depth, as shown in Table 10. 

Vertical Changes of Extractable Humic Substances in Lake Biwa Sediments"... 

Depth (m) Number of Samples Total Carbon (mg/g) Extractable Humic Substances (mg/g) Extractable Humic Substances Total Organic Matter"... 

Any attempt to design an effective procedure for the isolation of humic substances from soil should take account of the properties of the solvents or extractants to be used, of the solutes or material to be extracted, and of the types of associations that can exist between these solutes and other soil colloidal constituents. This chapter outlines some aspects of the composition, properties, and associations of soil humic substances which are relevant to their extraction, and it considers some of the properties of solvents that are used or might be considered for use as extractants of humic substances, or of molecules associated with these substances. It then compares the effectiveness and outlines some of the limitations of a selected number of solvents and procedures for dissolving and extracting humic substances. 

The extracted humic substances are free of inorganic contaminants, such as clay and polyvalent cations. 

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