This diploma thesis was focused on studying the interaction of humic substances with ionic organic xenobiotics and its structural aspects. The method was chosen from my bachelor thesis, steady-state fluorescence spectroscopy, which is suitable for substances with weak fluorescence. The results showed that the interaction between humic acids and representatives of ionic organic xenobiotics (Septonex) was reflected in fluorescence quenching of humic acids and the shift of emission maximum to lower wavelength, hypsochromic (blue) shift. From the measurement results, we can assume that the interaction that is formed between the aromatic structures in humic acids and Septonex could be -cation interaction.