The aquatic environment contains a wide range of dissolved or colloidal organic matter (DOM), which consists mainly of the products of decomposition of plant organic material. A major part of DOM is represented by humic substances (50-75% of total dissolved organic carbon (DOC)), of which 90% usually are fulvic acids (FAs) and 10% are humic acids [1]. DOM is a mixture of biogenic, mostly heterogeneous and refractory organic compounds. DOM interacts with many xenobiotics like PAH e.g., anthracene, pyrene, benzo(a)pyrene [2-4], PCB or DDT [5,6] by various modes of binding and adsorption such as ion exchange, hydrogen bonding, charge transfer, covalent binding or hydrophobic adsorption and partitioning [7,8]. Humic substances are not well defined because of their complex structure, but progress is being made in characterizing these substances according to their molar mass [9].