Angelika Anatolyevna Astaykina

Water-soluble organic substances (WSOM) of sod and humus horizons of Mollic Gleysol artificially saturated to full moisture capacity were isolated by sequential centrifugation from pores with a diameter of more than and less than 30 microns. The total concentration of carbon and phenolic compounds, the absorption and fluorescence spectra of the solutions do not differ significantly, but a strong variation in the parameters (the ratio of maximum and minimum values is 415 times) indicates the heterogeneity of the composition of the extracted substances. The concentration of simple phenolic acids in solutions of large pores of the humus horizon is 48 times higher than in smaller ones, salicylic, benzoic and cinnamic acids predominate (75% of the total amount). In small pores, p-hydroxybenzoic and benzoic acids predominate (67% of the total amount). Dissolved organic matter (DOM) of soil solution of the Podzolic soil (ELBTg horizon, moisture 22%), were obtained by tension lysimeters from pores with a diameter of more and less than 14.7 microns. DOM in solutions from large pores contain more C, N, phenolic compounds and, according to the absorption spectra, have a large molecular weight and a degree of aromaticity. Organic substances from small pores are more hydrophobic and are characterized by a greater C:N ratio; these features potentially promote DOM resistance to decomposition. Predominant localization of phenolic substances in large pores is favourable for the conservation in soil since transport with water flows assist their chemical stabilization in the lower horizons as organo-mineral compounds. 

A laboratory experiment was carried out to investigate the sorption behavior of 2.4-D onto two types of bentonite material: Na-Ca bentonite and organically modified bentonite (HDTMA-Br) using hexadecyltrimethylammonium bromide. The amount of HDTMA-Br was equivalent to the cation exchange capacity of the dominant mineral, montmorillonite, in the bentonites. The results showed that the organically modified bentonite absorbed 4.5 times more 2.4-D compared to the unmodified Na-Ca bentonite, indicating a significantly stronger sorption affinity for the organic cation. This finding suggests that organically modified bentonites may be more effective for the removal of 2.4-D from contaminated soil or water. In the range of pH values between 4 and 6, the sorption sites on the hydrophobic surface of organobentonite were found to have a relatively uniform energy for 2.4-d molecules (Freundlich constant n ≈ 0.8). Hydrophobic interactions were the dominant mechanism for the uptake of 2.4-D at these pH values. The possibility of using HDTMA-bentonite to reduce the mobility of 2.4-D in soils and landscapes, or to create new formulations, should be considered only after a thorough evaluation of the toxic effects of the organoclay on nontarget organisms.