The sorption coefficients to humic acid of 46 PAC having a wide range in polarity were compared with the capacity coefficients of the PAC to a non-polar HPLC column material (ODS) and a polar one (Diol). It is shown that polar interactions contribute to the sorption of polar PAC in addition to the non-polar interactions. The results also suggest that humic acid may contain different hydrophilic adsorption sites. The non-polar column material was only the best model substrate, if the test materials were limited to the hydrophobic unsubstituted PAC, PAH + O,S-PAC. (C) 1997 Elsevier Science B.V.