Molecular size distribution and hydrophilic and hydrophobic properties of humic acids isolated from forest soil

Abstract

Abstract:The aim of the present paper was to determine hydrophilic and hydrophobic properties and the degree of polydispersity of humic acids depending on their degree of maturity and the properties of the plant material participating in the process of humification. The study involved humic acids isolated from samples taken from organic and mineral horizons of forest soils. The samples were taken under the tree stands of: pine with an admixture of hardbeam, European beech, elm, fir, spruce, and thuja. It was demonstrated that the properties of humic acids of the organic horizon and mineral horizons are determined by the kind of plant litter, mainly by the tree species. The humification process is connected with an increase of the proportion of humic acids of lower molecular size as compared to the proportion of molecules greater in size, and with an increase of hydrophilic fractions and a decrease of hydrophobic fractions. Based on the correlation relationships, it was shown that the degree of polydispersity of molecules of humic acids is related to their hydrophilic and hydrophobic properties. Humic acids with a larger proportion of high-molecular fractions demonstrate also a higher proportion of hydrophobic fractions.

Effect of soil pollution with polycyclic aromatic hydrocarbons on the properties of humic acids

“…Parameter HIL/ΣHOB, as shown by, e.g. Debska et al (2007Debska et al ( , 2010Debska et al ( , 2012, is connected with the degree of organic matter humification; the value of the parameter increases with an increase in the degree of the maturity of the molecules of humic acids. In this experiment, after 180 days of incubation, the values of the HIL/ΣHOB ratio were similar to the values of the ratio of the HAs of the original soil samples.…”

“…The solutions of humic acids were applied in 0.01 mol L −1 NaOH at a concentration of 2 mg mL −1 ; injection of the sample, 100 μL; solvent-acetonitrile-water; solvents flow in the gradient (ratio H 2 O:ACN (v/v) over 0-6 min, 99.5:0.5; 7-13 min, 70:30; 13-20 min, 10:90) and detection at a wavelength of 254 nm. The share of hydrophilic (HIL) and hydrophobic (ΣHOB=HOB1+ HOB2) fractions in the humic acid molecules and the parameter HIL/ΣHOB were determined based on the areas that were determined under the peaks (Woelki et al 1997;Preuße et al 2000;Debska et al 2007). …”

“…2). Fractions of a retention time of 3.0-8.0 min show greater hydrophilic properties, whereas the fractions of a retention time between 12.0 and 25.0 min become more and more hydrophobic (Woelki et al 1997;Preuße et al 2000;Debska et al 2007Debska et al , 2010Debska et al , 2012. In the humic acids that were analysed, the share of the hydrophobic fraction was slightly higher than the share of the fraction containing compounds with hydrophilic properties (Table 5).…”

“…Preuβe et al (2000) and Debska et al (2007), the hydrophilic-hydrophobic parameters. According to Wen et al (2007), it is the polarity and the aromaticity of the humus fractions that are essential in the adsorption processes of PAHs.…”

Hydrophobic and hydrophilic properties of humic acids from soils under shelterbelts of different ages

“…Hydrophobic-hydrophilic properties of HA depend on their chemical composition, structure and conformation [17][18][19][38][39][40][41]. The most chemically mature peat HA fraction was shown to contain the highest proportion of hydrophilic components, whereas a less chemically mature HA fraction contained the largest amount of the most hydrophobic compounds.…”