Manufactured nanoparticles, like buckminsterfullerene (C-60), are characterized by unique surface chemistries and physical properties. As such they are expected to interact with, and subsequently foul, membrane surfaces in unconventional manners. C-60 nanoparticles were found to result in severe and rapid flux decline for a representative microfiltration (MF) membrane. The magnitude of flux loss that was observed was a function of the feed solution chemistry (pH, ionic strength) and generally followed expectations based on charge, van der Waals, and acid-base interactions. Permeate flux loss was determined to be a function of inter-particle interactions (aggregation state, cake packing density) and less a function of membrane-particle interactions in agreement with earlier studies. Cake filtration was found to best describe the flux loss resulting from C-60 nanoparticle fouling of the MF membrane; however, under unfavorable deposition conditions the nanoparticles, C-60 and a fluorescent nanospheres, were capable of passing through and depositing within the MF membrane structure. Therefore, standard pore blocking was also occurring at least during the initial stages of membrane fouling. (c) 2012 Elsevier B.V. All rights reserved.