Biological Activity of Native and Modified Humic Acids
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ogical Activity of Native and Modified Humic Acids S. I. Zherebtsova,*, N. V. Malyshenkoa,**, K. S. Votolina,***, K. M. Shpakodraeva,****, and Z. R. Ismagilova,***** a
Federal Research Center of Coal and Coal Chemistry, Siberian Branch, Russian Academy of Sciences, Kemerovo, 650000 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] ****e-mail: [email protected] *****e-mail: [email protected]
Received March 10, 2020; revised March 24, 2020; accepted March 30, 2020
Abstract—The samples of native and hydrogen peroxide–modified humic acids (HAs) separated from brown coals of the Tisul’skoe deposit in the Kansk-Achinsk Basin were obtained. The HA samples were characterized by instrumental methods: elemental and technical analysis and EPR spectroscopy. The modification of HAs affected the structural-group composition and decreased the concentration of paramagnetic centers (PMCs). The biological activity of native and modified humic acids was evaluated by phytotesting with the use of Iren varietal wheat seeds as an example. The highest biological activity was manifested at an HA concentration of 0.005%. A tendency toward a decrease in the biological activity with a decrease in the concentration of PMCs was revealed. Keywords: humic acids, biological activity, phytoactivity index, paramagnetic centers DOI: 10.3103/S0361521920040096
INTRODUCTION Humic acids (HAs) are structurally irregular natural high-molecular-weight compounds, which occur in peat, brown and oxidized coals, soil, and bottom sediments. HAs obtained from different sources differ in elemental composition, degree of condensation, substitution of aromatic nuclei, and a ratio between hydrophilic and hydrophobic fragments. The macromolecules of HAs include various (carbonyl, carboxyl, and hydroxyl) functional groups. Due to their unique structure, HAs can enter into redox reactions and complexation and ion-exchange reactions with metal cations, which in turn are responsible for a wide range of their applications [1]. As the sorbents of various metal cations, HAs are used to control chemical pollution, purify industrial effluents, detoxify contaminated soils, etc. They are used for the remediation and reclamation of degraded soils to improve their structure and to increase fertility. Recently, interest in the use of humic acids and preparations based on them as stimulants in agriculture has increased. As a result, crop yields and disease resistance were increased, and the influx of heavy metals and radionuclides into plants was reduced. At present, extensive experimental experience has been accumulated to testify a positive effect of the biological activity of humic substances on
the yield and quality of crops [2]. Semiquantitative relationships between the biological activity and the concentrations of paramagnetic centers (PMCs) [3], quinoid groups, and phenolic hydroxyls and the degree of aromaticity (fa) were found [4, 5]. It was demonstrated that a ratio between hydrophilic and hydrophobic fragments in the structure o
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