This study reports on the application of surface complexation modeling to interpret observed kinetic trends for Fell redox reactions with model nitroaromatic (4-chloronitrobenzene) and oxime carbamate (oxamyl) contaminants in aqueous TiO2(s) suspensions. Pseudo-first-order rate constants for reduction of the two probe contaminants (k(red), s(-1)) vary by several orders of magnitude with changing conditions (100-500 mu M Fe-II, 0-15 g L-1 TiO2(s), pH 2-9), but the relationship between reaction rates and Fe-II speciation differs considerably for the two contaminants. For oxamyl, k(red) measurements are most strongly correlated with the volumetric total adsorbed Fe-II concentration (moles Fe-II adsorbed per liter of TiO2(s) suspension), whereas k(red) measurements for 4-chloronitrobenzene are proportional to the concentration of the hydrolyzed Fe-II surface complex ((TiOFeOH0)-O-II). The differing trends demonstrate that Fe-II redox reactivity at the aqueous/TiO2(s) interface is influenced, in part, by specific molecular interactions with the target oxidant. Results are also geochemically relevant in that they demonstrate unambiguously that mononuclear Fe-II-metal (hydr)oxide surface complexes are sufficiently reactive species to reduce nitroaromatic contaminants, an issue that remained open following earlier studies in Fe-III (hydr)oxide suspensions because structural Fell species are simultaneously present in such systems because of interfacial Fe-II-to-Fe-III electron transfer processes that occur on Fell adsorption. (c) 2008 Elsevier Inc. All rights reserved.