title: Temporal changes in Aqu/C60 physical-chemical, deposition, and transport characteristics in aqueous systems.
abstract: Little is known about how temporal changes in the physical-chemical properties of C₆₀ aggregates formed in aqueous systems (termed aqu/C₆₀) can impact transport pathways contributing to ecological exposures. In this study three aqu/C₆₀ suspensions of short-term (100 days), intermediate-term (300 days), and long-term (1000 days) water exposure were first characterized for particle size distribution, water/toluene phase distribution, and surface chemistry. Then, aqu/C₆₀ deposition to a model silica surface and transport in porous media were studied by quartz crystal microbalance (QCM) and saturated sand columns. As suspension time increased, aqu/C₆₀ particle size shifted to a larger size range as determined by asymmetric flow field-flow fractionation (AF4) and the aqu/C₆₀ distribution to toluene was reduced, likely due to surface polarization as revealed by nuclear magnetic resonance (NMR) and UV-visible spectroscopy of the aqu/C₆₀ suspensions. Additionally, the deposition to silica surfaces in both QCM and column studies decreased with increased water exposure time. Although a small increase in aqu/C₆₀ aggregate size with time may partially explain the greater transport of the long-term aqu/C₆₀ because of the decreased collector efficiency for larger submicrometer particles, the polarization of the aqu/C₆₀ (thus a more hydrophilic surface) revealed by the toluene/water phase distribution and confirmed by NMR, is considered the determining factor.
authors.affiliation: National Exposure Research Laboratory, Office of Research and Development, U.S. EPA, Athens, Georgia, USA.
authors.forename: Carl
authors.initials: C
authors.lastname: Isaacson
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Tremaine
authors.initials: T
authors.lastname: Powell
authors.forename: Xin
authors.initials: X
authors.lastname: Ma
authors.forename: Dermont
authors.initials: D
authors.lastname: Bouchard
mesh_terms: D002021:Buffers; D055598:Chemical Phenomena; D031521:Fractionation, Field Flow; D037741:Fullerenes / Q000737:chemistry*; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D018625:Microscopy, Atomic Force; D008956:Models, Chemical; D008970:Molecular Weight; D009038:Motion; D010316:Particle Size; D058525:Quartz Crystal Microbalance Techniques; D012542:Scattering, Radiation; D012822:Silicon Dioxide / Q000737:chemistry; D012996:Solutions; D013535:Suspensions; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D002021:Buffers; D037741:Fullerenes; D012996:Solutions; D013535:Suspensions; D014867:Water; D012822:Silicon Dioxide