BOOK OF ABSTRACTS 227 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Hall A Poster Session / Environment, Agriculture, and Forestry P4.8 Diffusion of Sulphonamide Antibiotics in Model Humic Hydrogel Martina Klučáková1, Petra Závodská1 1 Brno University of Technology, Faculty of Chemistry, Purkyňova 118, 612 00 Brno, Czech Republic, klucakova@fch.vutbr.cz Humic substances are major constituents of soil organic matter responsible for its self-cleaning ability. The ability is based on the complexation of pollutants and their “locking” in humic structure. Formed complexes should have a high stability thus only very little amount can be leached in soil solution. Pollutants are complexed by soil organic matter (humic substances) during their migration in soil therefore we decided to study this problem as the diffusion in model medium – humic hydrogel, e.g. [1,2]. Sulphonamide antibiotics were chosen as pollutants because of their increased consumption connected with their input into environment. Sulphonamides are antibiotics widely used in livestock production which can enter agricultural soils by fertilization with contaminated manure. It can cause environmental and health risk which call for studies on the fate of antibiotics in soil [3-5]. Sulphapyridine and sulfamethoxazole were studied as representants of sulphonamide antibiotics. Humic acids were isolated from lignite mined in South Moravia (Czech Republic) [1,2,6]. Model humic hydrogel was prepared by the precipitation of sodium humate by hydrochloric acid, repeated washing ang and centrifugation [1,2,6]. Thus, the hydrogel is composed only of humic acids and water, where the content of humic acids corresponds to the content of organic matter in high quality soils. The method of diffusion from the instantaneous planar source was applied to hydrogel. It means that a little and defined amount of pollutant is placed at hydrogel surface and this “pulse” then diffuse into hydrogel volume. The hydrogel is prepared in the form of cylinder, its surface is isolated excepting frontal circular area available for the diffusion. The diffusion thus can be considered as one-dimensional which enables to use relatively simple mathematical model derived from Fick law on the basis of defined initial and boundary conditions. Experimental concentration profiles provided data for the calculation of diffusion coefficients of sulphonamides in the model humic hydrogel. Obtained diffusion coefficients were lower in comparison with the values valid for the diffusion of sulphonamide antibiotics in water. The reason is that the hydrogel obtained a solid network which can be considered as inaccessible for the diffusion therefore antibiotics can diffuse only in hydrogel pore structure filled
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