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Silver nanomaterials with different shapes (spheres, plates, wires, rods, cubes) are valued by industries and scientists for their shape-dependent properties which make them useful for diverse applications. In a safer-by-design perspective, controlling the shape of Ag nanomaterials could be an option to increase their properties while lowering either their hazard or their exposure potentials. Nine indoor aquatic mesocosms reproducing a lotic ecosystem were contaminated with chronic low-level additions of Ag nanospheres (Sp-Ag) and nanoplates (Pl-Ag) for a month. A shape-dependent impact under such environmentally relevant exposure conditions was observed. Pl-Ag induced a moderate oxidative stress in adult Gammarus fossarum(after molting) and a hormesis effect on planktonic microbial communities, while Sp-Ag had no effect. In an environmental risk perspective, our results highlight which ecological niches of a lotic ecosystem would be more impacted by Pl-Ag: (i) >72% of the total Ag was found fully sulfidized in surficial sediment and had only a moderate impact on benthic macro-organisms, (ii) only 11% to 15% of the Ag remained in the water column after 1 month, but Ag was under a more reactive speciation that impacts the planktonic community.

The colloidal and chemical stability of CeO2nanoparticles used in a diesel additive (viz.Envirox™) was studied at different stages of their lifecycle (formulation, use, end of life). After combustion at a temperature close to that of diesel engines, the size of the CeO2crystallites increased significantly without detectable Ce(iii) in the structure and remaining organic compounds at the surface. Regardless of the aging conditions (salinity, light, pH), the dissolution kinetics of the combusted particles were slowed down compared to that of the initial CeO2nanoparticles. After 2 days at 0.1 g L−1of salts, no more than 0.01% of the total Ce was released from the 850 °C-combusted Envirox™ versus1.5% for the uncombusted Envirox™. Both the crystal growth during combustion and the degradation of the organic matrix will govern the aggregation and dissolution kinetics/mechanisms once the CeO2particles are released into the environment at different stages of their lifecycle. Such a study is a prerequisite needed before any assessment of the environmental risks of CeO2nanoparticle-based diesel additives is performed.

The influence of membrane filtration modes on the estimation of size distribution for natural elements in water was investigated. The stepwise membrane filtration is used to distinguish different size fractions including large particulate (>18 μm), particulate (0.2–18 μm), colloidal/nanoparticle (10 kDa–0.2 μm), and truly dissolved fractions (<10 kDa) in river water samples and wastewater treatment plants effluents. Dead-end and tangential flow filtrations were compared during fractionation process. For most elements, concentrations in different size fractions obtained by two filtration modes were generally similar. The obvious difference was only found in acid fractions for some elements, which might be related to the cake grown at membrane surfaces between two filtration modes. In case of elemental partitioning, the influence of filtration modes was normally negligible, when the membranes used and operational factors were exactly the same.

AbstractThe influence of membrane filtration modes on the estimation of size distribution for natural elements in water was investigated. The stepwise membrane filtration is used to distinguish different size fractions including large particulate (>18 μm), particulate (0.2–18 μm), colloidal/nanoparticle (10 kDa–0.2 μm), and truly dissolved fractions (<10 kDa) in river water samples and wastewater treatment plants effluents. Dead-end and tangential flow filtrations were compared during fractionation process. For most elements, concentrations in different size fractions obtained by two filtration modes were generally similar. The obvious difference was only found in acid fractions for some elements, which might be related to the cake grown at membrane surfaces between two filtration modes. In case of elemental partitioning, the influence of filtration modes was normally negligible, when the membranes used and operational factors were exactly the same.

Indoor aquatic mesocosms were designed to mimic pond ecosystems contaminated by a continuous point-source discharge of cerium oxide nanoparticles (CeO2-NPs). Bare and citrate-coated CeO2-NPs exhibited different chemical and colloidal behaviors in the aquatic mesocosms. Bare CeO2-NPs were chemically stable but quickly homo-aggregated and settled out of the water column. Citrate-coated NPs both homo- and hetero-aggregated but only after the several days required to degrade the citrate coating. While they were more stable as a colloidal suspension, coated CeO2-NPs dissolved faster due to surface complexation with citrate, which resulted in the release of dissolved Ce into the water column. The different distributions over time between water/sediment or dissolved/particulate forms of Ce controlled the availability of Ce to benthic grazers (mollusk Planorbarius corneus) and planktonic filter feeders (copepod Eudiaptomus vulgaris).