Adsorption of zearalenone (ZEN) by natural zeolitic tuff, modified with different numbers of octadecyidimethylbenzylammonium (ODMBA) ions, was investigated. The results of solid-state H-1 NMR analysis of the starting material suggested that zeolitic tuff is rich in mineral clinop- tilolite, confirming the results of previous thermal stability study. Three organozeolites (OZ-2, OZ-5, and CZ-10) were prepared with ODMBA surface coverages of 20, 50, and 100 mmol/100 g. The mechanism of ZEN sorption by the three organozeolites was investigated through the determination of the adsorption isotherms at pH 3, 7, and 9. Adsorption of ZEN by organozeolites was best represented by a linear type of isotherm at pH 3, while at pH 7 and 9, adsorption of ZEN by organozeolites followed a nonlinear (Langmuir) type of isotherm. The different shape of the ZEN adsorption isotherms for the three organozeolites with different levels of ODMBA at the zeolitic surface at different pH values suggests that the adsorption mechanism may be dependent on the form of ZEN in solution. Since, at pH 3, ZEN exists in solution as the neutral form, the linear isotherms at pH 3 suggested that hydrophobic interactions are probably responsible for adsorption of neutral, hydrophobic ZEN onto the hydrophobic surface of the organozeolites. At pH 7, the phenolate anion is present in water solution, while at pH 9, ZEN is almost entirely in the anionic form. The nonlinear isotherms obtained for ZEN adsorption by the three organozeolites suggest that sorption appears to be the result of the adsorption process as well as partitioning. (C) 2007 Elsevier Inc. All rights reserved.