Numerous contaminated sites around the world bear witness to the fact that over the decades, polycyclic aromatic compounds (PACs) have been released into the environment on a large scale by human activity. PAC contaminations still constitute a source of eminent risks for human health. Such contaminations often coincide with natural organic matter in both soil and water. Natural organic matter is largely composed of humic substances (HSs), which together with non-HSs form a so-called system of HSs (SHS) . HSs are presumed to account for a considerable part of PAC sorption . The structural diversity found in HSs samples results in a variety of interactions between PACs and HSs, starting from sorption phenomena and ending with conversions of the PACs’ molecular skeleton in the process of humification. Humification is accomplished by microbial action and/or in a purely chemical way. Sorption may be the first step of chemical transformations in humification. Chemical PAC conversion and microbial degradation both are affected by sorption.