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ISSN 0147 6874, Moscow University Soil Science Bulletin, 2010, Vol. 65, No. 4, pp. 151­154. © Allerton Press, Inc., 2010. Original Russian Text © N.A. Kulikova, I.V. Perminova, 2010, published in Vestnik Moskovskogo Universiteta. Pochvovedenie, 2010, No. 4, pp. 16­19.

A Comparative Study of Elemental Composition of Water Soluble Humic Substances, Humic Acids, and Fulvic Acids Extracted from Sod­Podzolic Soils
N. A. Kulikova and I. V. Perminova
Received March 14, 2010

Abstract--Elemental analysis of water soluble humic substances extracted from three sod­podzolic soils was carried out. Data on elemental composition were compared to those of humic and fulvic acids extracted from the same soils. Keywords: water soluble humic substances, elemental composition. DOI: 10.3103/S0147687410040034

Humic substances (HSs) of the soil solution repre sent the most soluble part of humus; this determines their high mobility and activity with respect to biota [12]. In a series of works, the effects of dissolved organic substances were demonstrated on the interac tions of contaminating substances with soil compo nents; this resulted in the change in their condition and, as a consequence, an increase [6­8, 13] or decrease [9, 10] in their mobility and a change in their bioavailability [5]. Thus, the study of the HS of the soil solution is a topical problem that has interest for both practical and theoretical agrology. The purpose of this work is to compare the elemen tal composition of water soluble humic substances (WHSs) of sod­podzolic soils of various states of cul tivation and the humic and fulvic acids that were iso lated from these soils. MATERIALS AND METHODS In order to isolate the preparations of HSs, three soils were used from the areas of various state of culti

vation: virgin sod­podzolic weakly soddy deep­pod zolic medium loamy on the limon under the forest (SSV), cultivated sod­podzolic medium tillable medium loamy weakly eroded on the limon (SSC), and arable sod­podzolic deep tillable medium loamy (SSA). Individual samples (each was about 20 kg) were taken from a section with an area of ~10 m2 from the upper humous horizon at a depth of 0­5 cm. In the virgin version, the layer was preliminarily removed. Selected samples were dried to an air dry state and passed through a sieve with a cell diameter 1 mm. From the prepared soil an average sample was made, which was used for chemical analyses and isolation of HS preparations. The properties of soils determined by the known procedures [1] and the names of the preparations isolated from them are given in Table 1. Humic acids were separated using the standard procedure by extraction with 0.1 M NaOH with fur ther acidification to a pH of 1­2 by 0.1 M HCl [4]. The preparations were purified with electrodialysis. Fulvic acids were separated by the method used for natural waters [11]: the solution that remained after

Table 1. Chemical properties of soils and conventional signs of the preparations of humic substances isolated from them pH pHKCl OC, % Sum of HH CHA/CFA exchange bases mg eq./100 g WHS HA limon HA­SSV the limon HA­SSC HA­SSA FA

H2 O

5.0 7.8 7.3

Virgin sod­podzolic weakly soddy deep podzolic medium loamy soil on the 4.5 4.3 0.2 7.2 5.5 WHS­SSV Cultivated sod­podzolic medium tillable medium loamy weakly eroded soil on ­ 1.5 0.7 17.1 2.0 WHS­SSC Arable sod­podzolic deep tillable medium loamy soil ­ 3.8 0.3 37.1 1.3 WHS­SSA 151

FA­SSV FA­SSC FA­SSA


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Table 2. Elemental composition of isolated preparations of WHS, HA, and FA Preparation Elemental composition (wt % on ash free anhydrous sample) C WHS­SSV WHS­SSC WHS­SSA FA­SSV FA­SSC FA­SSA HA­SSV HA­SSC HA­SSA 45.6 37.5 48.2 56.4 50.2 55.1 59.0 52.1 54.6 H 5.6 3.6 6.9 4.7 4.9 4.8 5.0 5.9 5.6 N H/C Atomic ratios O/C C/N 0 0 172 30 19 23 16 11 20 60.4 46.7 30.8 8.4 2.4 6.9 9.4 2.2 1.2 Ash content, %

Water soluble humic substances * 1.48 0.70 * 1.16 1.05 0.3 1.74 0.59 Fulvic acids 2.2 0.99 0.41 3.2 1.17 0.53 2.8 1.04 0.42 Humic acids 4.4 1.02 0.32 5.3 1.36 0.44 3.3 1.22 0.42

Note: * less than the detection limit.

the precipitation of HA was put through a column filled with Amberlite XAD 2 resin with further wash ing of chloride ions and desorption of FA from the resin by 0.1 M NaOH. The preparations that were obtained were purified using electrodialysis. Preparations of water soluble humic substances. A sample (1 kg) of air dry soil passed through a sieve with a mesh size of 1 mm was filled with two liters of distilled water, thoroughly shaken, and left for a night. The aqueous extract was filtered through a Blue Rib bon paper filter and a membrane filter with a pore diameter of 0.45 µm for the separation of true dis solved organic substance from the colloidal. The pro cedure was carried out with 10 kg of each soil used. Filtered extracts were combined, acidified to pH 1­2
H/C 2.0 1 1.8 1.6 1.4 1.2
HA FA Water soluble humic substances

2

3

with 0.1 M HCl and put through a glass column filled with Amberlite XAD 2 resin for the separation of WHSs. Elution of the WHS preparation from the col umn and further desalination were analogous to those described for the separation of FA. The elemental composition of the preparations of humic substances was determined on a Carlo Erba Strumentazione 1106 CHN analyzer (Italy); ash content was determined by combustion in a quartz tube (850°C; 40 min). The content of oxygen was cal culated by the difference between the mass of the sam ple and the total content of ash and CHN. The composition of the ash of HSs was determined by atom emission spectroscopy with atomization of the sample in induction bonded plasma (AES IBP). The element composition (Al, B, Ca, Cu, Fe, K, Mg, Mn, Na, Si, Ti, and Zn) was determined in salt free solutions used for solid preparations (WHS and FA) or in solutions prepared by the dissolution of the sample in 0.1 M KOH (HA preparations). RESULTS AND DISCUSSION Preparations substantially differed by their elemen tal composition (Table 2). Atomic ratios (H/C) varied in the range of 0.99­1.74; this agrees well with the data of other researchers [3]. An increase in this value was observed in the sequence FA < HA < WHS. This con firms that along the preparations under study water soluble humic substances have maximum unsatura tion. The maximum values of the O/C ratio character ize the oxidation of the macromolecules of humic acids were noted for WHS of the virgin sod­podzolic soil. For HA­FA pairs isolated from one soil, the higher O/C value was observed for FA preparations
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1.0 0.8 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 O/C
Arrangement of the preparations of humic substances of sod­podzolic soils on a Van­Krevelen diagram: (1) SSV, (2) SSC, and (3) SSA.

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A COMPARATIVE STUDY OF ELEMENTAL COMPOSITION Table 3. The content of the ash in the preparations of WHS, HA, and FA, calculated from the data of AES IBP Content of the ash form of the mineral element, mg/g of organic substance Preparation Na2CO3 K2CO3 CaCO3 MgCO3 Al2O3 WHS­SSV WHS­SSC WHS­SSA FA­SSV FA­SSC FA­SSA HA­SSV HA­SSC HA­SSA 72.3 29.2 30.4 6.2 18.6 25.5 39.0 58.8 49.8 1.8 1.9 1.6 170.0 963.1 21.5 ­* ­ ­ 8.6 4.8 7.1 1.3 13.9 9.4 0.8 1.6 0.9 Water 1.2 1.5 1.0 0.2 0.4 0.5 0.3 1.4 0.7 Fe2O3 SiO2 TiO2 0.4 0.2 0.3 0.1 0.1 0.2 0.4 0.3 0.1 MnO2 1.37 0.95 2.12 0.17 0.52 0.56 0.24 0.30 0.28 ZnO2 0.39 0.15 0.28 0.07 0.10 0.29 0.03 0.15 0.06 B2O3 2.7 1.6 3.2 1.2 3.3 9.6 0.2 0.3 0.3

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CuO 0.13 0.14 0.22 0.02 0.16 0.09 0.03 0.05 0.05

soluble humic substances 3.5 1.9 2328 1.6 0.7 618 3.9 1.6 921 Fulvic acids 0.8 0.4 14 1.7 0.6 47 2.9 1.9 100 Humic acids 2.9 3.1 5 6.8 2.5 16 4.4 1.5 11

Note: * the determination of potassium in HA solutions was not carried out, because solutions prepared from 0.1 M KOH were used for AES IBP analysis.

enriched in oxygen containing functional groups. On the whole, the O/C ratio was in the following order: HA < FA < WHS. It is noteworthy that nitrogen was practically not detected in WHS preparations. An exception was made for the preparation obtained from arable soil; this can probably be determined by the introduction of nitrogen fertilizers into the soil. The Van Krevelen diagram built on the basis of the data obtained (figure), vividly demonstrates the differ ences in the elemental composition of the prepara tions of humic acids. As follows from the figure, humic substances of the water extract are more hydrated with respect to fulvic acids and the latter, in turn, are enriched with carboxylic groups compared to humic acids. Thus, on the basis of the data of the elemental anal ysis it can be concluded that in comparison with humic and fulvic acids water soluble humic sub stances have elevated unsaturation levels and are enriched with oxygen containing functional groups and depleted in nitrogen. The data from Table 2 confirm the abnormally high ash content of the isolated preparations of humic sub stances of the water extract. Therefore, they were ana lyzed for their contents of mineral elements by AES IBP. Using the results thus obtained and knowing the concentration of HSs, the molar content of the ele ment in the preparation was calculated. After this, on the basis of the chemical properties of the given ele ment and the conditions of the determination of the ash content (combustion of the preparation in an oxy gen flow at 850°C), the form was proposed that it con tains in the ash [2]. So, due to the thermostability of the alkaline and alkaline earth metal carbonates, we
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proposed that they form carbonates in the conditions of the experiment, and other metals form oxides. On the basis of the obtained values the mass of the ash form was calculated for each element on the unity of the organic substance of humic substances. The results are given in Table 3. As follows from Table 3, the main ash compo nents are silicon, calcium, aluminum, iron, and potassium. The preparations can be arranged in the following order by an increase in the content of sili con: HA < FA < WHS. Assuming that the procedure of the isolation of the preparations of humic acids of the water extracts of the soils included filtration through 0.45 µm membrane filter, it can be concluded that silicic acid fragments are strictly bonded to humic substances and these are not mechanical admixtures. This probably confirms that during the extraction of the isolated preparations the humic acids are mainly represented by organomineral compounds. ACKNOWLEDGMENTS This work was supported by the Russian Founda tion for Basic Research, project no. 10 03 00803 a, Program of the interdisciplinary scientific projects of Moscow State University 2007 and 2008, and the Ministry of Education and Science of the Russian Federation (GK P211). REFERENCES
1. Arinushkina, E.V., Rukovodstvo po khimicheskomu analizu pochv (Manual on Soils Chemical Analysis), Moscow: MGU, 1970.
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KULIKOVA, PERMINOVA 8. Grabr, E.R., Gerstl, Z., Fischer, E., and Mingelgrin, U., Enhanced Transport of Atrazine under Irrigation with Effluent, Soil. Sci. Soc. Amer. J., 1995, no. 59, pp. 1513­1519. 9. Guo, L., Bicki, T.J., Felsot, A.S., and Hinesly, T.D., Sorption and Movement of Alachlor in Soil Modified by Carbon Rich Wastes, J. Environ. Qual., 1993, no. 22, pp. 186­194. 10. Johnson, A., Worral, F., White, C., et al., The Potential of Incorporated Organic Matter to Reduce Pesticide Leaching, Toxicol. Environ. Chem., 1997, no. 58, pp. 47­61. 11. Mantoura, R.F.C. and Riley, J.R., The Use of Gel Fil tration in the Study of Metal Binding by Humic Acids and Related Compounds, Anal. Chim. Acta, 1975, no. 78, pp. 193­200. 12. McCracken, K.L., McDowell, W.H., Harter, R.D., and Evans, C.V., Dissolved Organic Carbon Retenition in Soils: Comparison of Solution and Soil Measurements, Soil. Sci. Soc. Amer. J., 2002, no. 66, pp. 563­568. 13. Nelson, S.D., Letey, J., Farmer, W.J., et al., Facilitated Transport of Nanopropamid by Dissolved Organic Matter in Sewage Sludge Amended Soil, J. Environ. Qual., 1998, no. 27, pp. 1194­1200.

2. Zhilin, D.M., Research of Reaction Ability and Detox ication Properties of Humic Acids with Respect to Hydrargyrum (II) Compounds, Cand. Sci. (Chem.) Dis sertation, Moscow, 1998. 3. Orlov, D.S., Khimiya pochv (Soil Chemistry), Moscow: MGU, 1992. 4. Orlov, D.S. and Grishina, L.A., Praktikum po khimii gumusa (Practical Works on Humus Chemistry), Mos cow: MGU, 1981. 5. Bolan, N.S., Adriano, D.C., Natesan, R., and Koo, B. J., Effects of Organic Amendments on the Reduction and Phytoavailability of Chromate in Mineral Soil, J. Environ. Qual., 2003, no. 32, pp. 120­128. 6. Chiou, C.T., Malcom, R.L., Brinton, T.I., and Kile, D.E., Water Solubility Enhancement of Some Organic Pollutants and Pesticides by Dissolved Humic and Fulvic Acids, Environ. Sci. Technol., 1986, no. 20, pp. 502­508. 7. Flores CÈspedes, F., GonzeÀlez Pradas, E., FernÀn dez PÈrez, M., et al., Effects of Dissolved Organic Car bon on Sorption and Mobility of Imidacopiralid in Soil, J. Environ. Qual., 2002, no. 31, pp. 880­888.

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