The polydisperse composition of nine dissolved organic materials (DOMs) from two river water sources, one ground water source, two biologically treated wastewater sources, and two commercial sources was analyzed based on their adsorbabilities by activated carbon. For each DOM, batch adsorption isotherms measured for both TOC and UV260 were analyzed using an overall isotherm model derived from the IAST-Freundlich expression. By accounting for the heterogeneity of each DOM with a log-normal distribution of the Freundlich parameter (K), its adsorption behavior was characterized with only four parameters (including three fitting ones). The average adsorptive strength (Km) and heterogeneity (a) determined for all DOMs, which were defined by the mean value and the standard deviation of the log-normal distribution of the Freundlich K, changed over the ranges 2.5-62.2 and 0.22-0.97 (mg/g)/(mg/l)(l/n), respectively, when the TOC index was used. Among all DOMs studied, a river water DOM at the upper stream was found least heterogeneous: the Freundlich K of its organic constituents varied in the range 10.8-190 (mg/g)/(mg/l)(l/n), as compared to a commercial humic acid that exhibited the broadest Freundlich K distribution of 0.01-1494.3 (mg/g)/(mg/l)(l/n). K-M and sigma along with other two parameters (the Freundlich exponent l/n and the nonadsorbable organic fraction parameter C-non/C-T0), changed with both indices of TOC and UV260 in a regular manner, indicating that UV-absorbing organic molecules possessed adsorbabilities different from non-UV-absorbing ones. Also based on HPSEC chromatograms measured for solutions before adsorption, the molecular weight composition of all DOMs was also assessed and the molecular size impacts on adsorption characteristics of DOMs were briefly discussed. (C) 2003 Elsevier Inc. All rights reserved.