Transformations and long-term fate of engineered nanomaterials must be measured in realistic complex natural systems to accurately assess the risks that they may pose. Here, we determine the long-term behavior of poly(vinylpyrrolidone)-coated silver nanoparticles (AgNPs) in freshwater mesocosms simulating an emergent wetland environment. AgNPs were either applied to the water column or to the terrestrial soils. The distribution of silver among water, solids, and biota, and Ag speciation in soils and sediment was determined 18 months after dosing. Most (70 wt %) of the added Ag resided in the soils and sediments, and largely remained in the compartment in which they were dosed. However, some movement between soil and sediment was observed. Movement of AgNPs from terrestrial soils to sediments was more facile than from sediments to soils, suggesting that erosion and runoff is a potential pathway for AgNPs to enter waterways. The AgNPs in terrestrial soils were transformed to Ag 2 S (∼52%), whereas AgNPs in the subaquatic sediment were present as Ag 2 S (55%) and Ag-sulfhydryl compounds (27%). Despite significant sulfidation of the AgNPs, a fraction of the added Ag resided in the terrestrial plant biomass (∼3 wt % for the terrestrially dosed mesocosm), and relatively high body burdens of Ag (0.5−3.3 μg Ag/g wet weight) were found in mosquito fish and chironomids in both mesocosms. Thus, Ag from the NPs remained bioavailable even after partial sulfidation and when water column total Ag concentrations are low (<0.002 mg/L).

We investigated how leaf hydraulic conductance (Kleaf) of loblolly pine trees is influenced by soil nitrogen amendment (N) in stands subjected to ambient or elevated CO2 concentrations (CO2 a and

International audienceIn this study, we present a method for determining the relative affinity of nanoparticles (NPs) for an ensemble of other particles in a complex, heterogeneous suspension. We evaluated this method for NPs heteroaggregating with suspended solids present in activated sludge. A relationship was derived between the heterogeneous affinity coefficient, alpha, and measurements over time of the distribution coefficient, gamma, of NPs measured in supernatant versus those removed by heteroaggregation and subsequent settling. Application of this method, which uses a mathematical relationship to determine alpha from experimentally measured gamma values, to a series of metal and metal oxide NPs heteroaggregated with activated sludge indicated a relative affinity in the order of pristine CeO2, TiO2 NPs, and ZnO NPs > Ag(0) NPs surface-modified with polyvinylpyrrolidone (PVP) > citrate-functionalized CeO2 NP > Ag(0) NPs surface-modified with gum arabic. This trend in relative affinity followed the observed trend in removal such that higher affinity corresponded to higher removals of NPs. Values of alpha were calculated from measured relative affinities using average diameter and concentration of the activated sludge particles. The value calculated for PVP-stabilized Ag(0) NPs was comparable to a value previously reported for the attachment of these same NPs to a biofilm. Calculations also yielded size dependence of alpha in the case of the two Ag(0) evaluated that may be linked to NP dissolution

Properties of nanomaterial suspensions are typically summarized by average values for the purposes of characterizing these materials and interpreting experimental results. We show in this work that the heterogeneity in aqueous suspensions of fullerene C60 aggregates (nC60) must be taken into account for the purposes of predicting nanomaterial transport, exposure, and biological activity. The production of reactive oxygen species (ROS), microbial inactivation, and the mobility of the aggregates of the nC60 in a silicate porous medium all increased as suspensions were fractionated to enrich with smaller aggregates by progressive membrane filtration. These size-dependent differences are attributed to an increasing degree of hydroxylation of nC60 aggregates with decreasing size. As the quantity and influence of these more reactive fractions may increase with time, experiments evaluating fullerene transport and toxicity end points must take into account the evolution and heterogeneity of fullerene suspensions.

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