The interactions between trace organics, nanofiltration (NF) polymeric membrane material, fouling layers and macromolecules present in aqueous solution were assessed. Through a specific series of experiments, better characterisation of the impact of each individual mechanisms affecting the membrane rejection of trace organics was obtained. A full mass balance study was conducted to characterise the fate of the trace organics during water treatment by NF. The levels of adsorption of trace organics onto the membrane surface and association with the macromolecules were shown to strongly relate with the physicochemical properties of the trace organics as well as the molecular weight of the organic matter macromolecules. The results of this study revealed that two counteractive mechanisms were commonly involved in the rejection of nonionic solutes: (1) adsorption onto macromolecules resulting in increased rejection and (2) presence of cake enhanced concentration polarization leading to decrease in rejection. (C) 2011 Elsevier B.V. All rights reserved.