The irreplaceable role of natural organic matter in contaminant transport in the ecosystem is well-known. Especially, the complexation of charged compounds by humic acids represents the process of exceptional environmental importance. Nevertheless, traditional methods utilized in the complexation studies (equilibrium or kinetic sorption experiments) do not address the way, how these interactions affect the transport of ions in humic-rich environments, properly. This contribution summarizes the rich collection of experiments which have recently focus on utilization of simple transient and steady-state diffusion experiments in revealing the effect of interactions of charged organic compounds (low-molecular cationic dyes) with humic acids fixed in a suitable hydrogel matrix (agarose gel). The hydrogel support is used in order to simulate the state of the humics in their natural environments and also to allow preparation of samples in the properly described form (in sense of their size and shape) which is necessary for correct data evaluation. Diffusion-cell and in-diffusion experiments have been performed in to determine the effective diffusion coefficients of the model charged organic compounds in hydrogels with different content of humic substances. Results were interpreted using the comprehensive theoretical model, derived for the diffusion of solutes in the porous media, to provide some structural (tortuosity) and interaction (binding constants) parameters of the studied systems. Effects of various experimental conditions (pH, temperature, ionic strength) were studied to better understand the origin of the humics-dye interactions. In addition, the specific role of carboxylic groups of the humic acids was revealed by insertion of the site-selective methylation of the carboxyls prior to the diffusion experiments.

Role of humic acids in transport of charge organic compounds as revealed by combination of simple laboratory diffusion techniques

248th National Meeting (2014)

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