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Praetorius A.,ETH Zurich | Labille J.,Aix - Marseille University | Scheringer M.,ETH Zurich | Thill A.,International Consortium for the Environmental Implications of Nanotechnology | And 3 more authors.
Environmental Science and Technology | Year: 2014

The heteroaggregation of engineered nanoparticles (ENPs) with natural colloids (NCs), which are ubiquitous in natural surface waters, is a crucial process affecting the environmental transport and fate of ENPs. Attachment efficiencies for heteroaggregation, αhetero, are required as input parameters in environmental fate models to predict ENP concentrations and contribute to ENP risk assessment. Here, we present a novel method for determining αhetero values by using a combination of laser diffraction measurements and aggregation modeling based on the Smoluchowski equation. Titanium dioxide nanoparticles (TiO2 NPs, 15 nm) were used to demonstrate this new approach together with larger silicon dioxide particles (SiO2, 0.5 μm) representing NCs. Heteroaggregation experiments were performed at different environmentally relevant solution conditions. At pH 5 the TiO2 NPs and the SiO2 particles are of opposite charge, resulting in αhetero values close to 1. At pH 8, where all particles are negatively charged, αhetero was strongly affected by the solution conditions, with αhetero ranging from <0.001 at low ionic strength to 1 at conditions with high NaCl or CaCl2 concentrations. The presence of humic acid stabilized the system against heteroaggregation. © 2014 American Chemical Society. Source

Auffan M.,Aix - Marseille University | Auffan M.,Duke University | Matson C.W.,International Consortium for the Environmental Implications of Nanotechnology | Matson C.W.,Duke University | And 17 more authors.
Nanotoxicology | Year: 2014

We assessed the biodistribution and in situ speciation of sub-lethal concentrations of citrate-coated silver nanoparticles and dissolved silver within Fundulus heteroclitus embryos. Using a thorough physico-chemical characterization, we studied the role of salinity on both uptake and in situ speciation. The Ag uptake or adsorption on the chorion was reduced by 2.3-fold for Ag NPs, and 2.9-fold for AgNO3 in estuarine water (10‰ ASW) compared to deionized water (0‰ ASW). Between 58% and 85% of the silver was localized on/in the chorion and formed patches between 20 and 80 μm. More than a physical barrier, the chorion was found to be a chemically reactive membrane controlling the in situ speciation of silver. A strong complexation of the Cit-Ag NPs with the thiolated groups of proteins or enzymes of the chorion was responsible for the oxidation of 48 ± 5% of the Ag0 into Ag(I)-S species at 0‰ ASW. However, at 10% ASW, the presence of Cl- ions at the surface of Ag NPs slow down this oxidation. For the dissolved silver, we observed that in deionized water 69 ± 7% of Ag+ taken up by the chorion was complexed by the thiolated molecules while the others 30 ± 3% were reduced into Ag0 likely via interaction with the hemiacetal-reducing ends of polysaccharides of the chorion. © 2014 Informa UK Ltd. All rights reserved. Source

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