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Site specific exposure assessments for engineered nanoparticles (ENPs) require spatially explicit fate models, which however are not yet available. Here we present an ENP fate model (NanoDUFLOW) that links ENP specific process descriptions to a spatially explicit hydrological model. The link enables the realistic modelling of feedbacks between local flow conditions and ENP fate processes, such as homo- and heteroaggregation, resuspension and sedimentation. Spatially explicit simulations using five size classes of ENPs and five size classes of natural solids showed how ENP sediment contamination ‘hot spots’ and ENP speciation can be predicted as a function of place and time. For the catchment modelled, neglect of spatial heterogeneity caused relatively small differences in ENP retention. However, simplification of the number of size classes to one average class, resulted in up to 3.3 times lower values of retention compared to scenarios that used detailed size distributions. Local concentrations in sediment were underestimated up to 20 fold upon simplification of spatial heterogeneity or particle size distribution. We conclude that spatial heterogeneity should not be neglected when assessing the risks of ENPs. [ABSTRACT FROM AUTHOR]

Parameters and simplified model approaches for describing the fate of engineered nanoparticles (ENPs) are crucial to advance the risk assessment of these materials. Sedimentation behavior of ENPs in natural waters has been shown to follow apparent first order behavior, a 'black box' phenomenon that is insufficiently understood and therefore of limited applicability. Here we use a detailed Smoluchowski-Stokes model that accounts for homo- and heteroaggregation and sedimentation of ENPs and natural colloids (NCs), to simulate and interpret experimental ENP aggregation-sedimentation data. The model adequately simulated the observed time and initial concentration dependence of CeO2 settling data, and also predicted the conditions for aggregation rate-limitations of overall removal. Heteroaggregation with natural colloids was identified as the dominating removal process. Finally, the empirical apparent first order model data were calibrated against the mechanistic Smoluchowski-Stokes model simulation data, showing excellent fits for a range of NC initial concentrations. Using first order removal rates thus can be considered a valid and informed approximation when modeling ENP fate in the aquatic environment. [ABSTRACT FROM AUTHOR]

Sedimentation of engineered nanoparticles (ENPs) has been studied mainly in artificial media and stagnant systems mimicking natural waters. This neglects the role of turbulence and heteroaggregation with sediment. The authors studied the apparent sedimentation rates of selected ENPs (cerium dioxide [CeO2], polyvinylpyrrolidone-capped silver [PVP-Ag], and silica-coated silver [SiO2-Ag]) in agitated sediment-water systems resembling fresh, estuarine, and marine waters. Experiments were designed to mimic low energy and periodically resuspended sediment water systems (14 d), followed by a long-term aging, resuspension, and settling phase (6 months), as would occur in receiving shallow lakes. The ENPs in systems with periodical resuspension of sediment were removed with sedimentation rates between 0.14 m/d and 0.50 m/d. The sedimentation rates did not vary much among ENP type, salinity, and aging time, which is attributed to the capture of ENPs in sediment flocks. The sedimentation rates were 1 to 2 orders of magnitude higher than those reported for aggregation-sedimentation in stagnant systems without suspended sediment. Heteroaggregation rates were estimated and ranged between 0.151 L/mg/d and 0.547 L/mg/d, which is up to 29 times higher than those reported for natural colloids under quiescent settling conditions. The authors conclude that rapid scavenging and sedimentation drives removal of ENPs from the water column. Environ Toxicol Chem 2014;33:1766-1773. © 2014 SETAC [ABSTRACT FROM AUTHOR]

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 CeO2 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 CeO2 nanoparticle suspensions, homoaggregation is likely the main mechanism leading to sedimentation. The proposed model could form the basis for improved exposure assessment for nanomaterials. Environ. Toxicol. Chem. 2012; 31: 1019-1022. © 2012 SETAC [ABSTRACT FROM AUTHOR]

Abstract: The ecological risk assessment of chemicals including nanoparticles is based on the determination of adverse effects on organisms and on the environmental concentrations to which biota are exposed. The aim of this work was to better understand the behavior of nanoparticles in the environment, with the ultimate goal of predicting future exposure concentrations in water. We measured the concentrations and particle size distributions of CeO2 nanoparticles in algae growth medium and deionized water in the presence of various concentrations and two types of natural organic matter (NOM). The presence of natural organic matter stabilizes the CeO2 nanoparticles in suspension. In presence of NOM, up to 88% of the initially added CeO2 nanoparticles remained suspended in deionized water and 41% in algae growth medium after 12d of settling. The adsorbed organic matter decreases the zeta potential from about −15mV to −55mV. This reduces aggregation by increased electrostatic repulsion. The particle diameter, pH, electric conductivity and NOM content shows significant correlation with the fraction of CeO2 nanoparticles remaining in suspension. [ABSTRACT FROM AUTHOR]

Abstract The aim of this paper is to present a new, integrative approach for calculating Fate Factors ( FF ) for nanomaterials by combining the USEtox2.0 modelling framework with SimpleBox4Nano (SB4N), an advanced environmental fate model for nanomaterials, and to demonstrate its application to life cycle assessment (LCA) by the estimation of characterisation factor ( CF ) for nano-TiO 2 for the impact category of freshwater ecotoxcity. To enable the combination of the USEtox model with SB4N, two principle adaptations were made: (i) the compartments of air and rain were merged, and (ii) the sum of the free, aggregated, and attached species was accounted for in the receiving compartments. Furthermore, a dynamic analysis was conducted to characterize the dynamic behaviour of nanoparticles and to estimate the time at which steady state is actually reached. Our combined USEtox-SB4N approach was then applied to calculate i) the Fate Factor ( FF ) for unitary emissions of nano-TiO 2 to air, freshwater, soil and sediment, and ii) using these, characterisation factors (CF) for nano-TiO 2 in the case of the impact category freshwater ecotoxicity. The FF for unitary emissions of nano-TiO 2 as free species was calculated. Persistence was found to be highest for emissions to soil (FF s,s = 2.9·105 days), followed by emissions to water (FF w,w = 128 days) and, then for an emissions to air ( FF a,a = 3.3 days). The results of the dynamic analysis showed that the soil compartment in fact behaves as a storage compartment. Finally, an update of the freshwater ecotoxicity CF for nano-TiO 2 was calculated ( CF = 3443 PAF day m3 kg−1), based on the here established FF. The integrative approach presented here for calculating nano-specific FF values serves to reduce the complexity of the S4BN model and make the USEtox modelling framework fit for use with nanomaterials. This approach can be seen as a first step towards a "USEtox4Nano" characterisation model. Highlights • Lack of characterisation factors (CF) for impact assessment of nanomaterial releases. • Integrative approach for calculating FF for ENPs by combining the USEtox 2.0 and SB4N. • Reducing the complexity of the S4BN model and make the USEtox 2.0 fit for ENP. • For TiO2, aggregated species are dominant in air and water, attached species in soil and sediments. • Species fractions depend on emission compartment, a fixed proxy providing acceptable fate factors. [ABSTRACT FROM AUTHOR]