title: Natural colloids are the dominant factor in the sedimentation of nanoparticles.
abstract: Estimating the environmental exposure to manufactured nanomaterials is part of risk assessment. Because nanoparticles aggregate with each other (homoaggregation) and with other particles (heteroaggregation), the main route of the removal of most nanoparticles from water is aggregation, followed by sedimentation. The authors used water samples from two rivers in Europe, the Rhine and the Meuse. To distinguish between small (mainly natural organic matter [NOM]) particles and the remainder of the natural colloids present, both filtered and unfiltered river water was used to prepare the particle suspensions. The results show that the removal of nanoparticles from natural river water follows first-order kinetics toward a residual concentration. This was measured in river water with less than 1 mg L(-1) CeO(2) nanoparticles. The authors inferred that the heteroaggregation with or deposition onto the solid fraction of natural colloids was the main mechanism causing sedimentation in relation to homoaggregation. In contrast, the NOM fraction in filtered river water stabilized the residual nanoparticles against further sedimentation for up to 12 d. In 10 mg L(-1) and 100 mg L(-1) CeO(2) nanoparticle suspensions, homoaggregation is likely the main mechanism leading to sedimentation. The proposed model could form the basis for improved exposure assessment for nanomaterials.
authors.affiliation: Institute for Wetland and Water Research, Department of Environmental Science, Radboud University Nijmegen, Nijmegen, The Netherlands. joris.quik@wur.nl
authors.forename: Joris T K
authors.initials: JT
authors.lastname: Quik
authors.forename: Martien Cohen
authors.initials: MC
authors.lastname: Stuart
authors.forename: Marja
authors.initials: M
authors.lastname: Wouterse
authors.forename: Willie
authors.initials: W
authors.lastname: Peijnenburg
authors.forename: A Jan
authors.initials: AJ
authors.lastname: Hendriks
authors.forename: Dik
authors.initials: D
authors.lastname: van de Meent
mesh_terms: D055598:Chemical Phenomena; D003102:Colloids / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry; D009426:Netherlands; D045483:Rivers / Q000737:chemistry*; D013535:Suspensions / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D003102:Colloids; D013535:Suspensions; D014874:Water Pollutants, Chemical