Cerium dioxide nanoparticles (CeO2 NPs) are increasingly being used as a catalyst in the automotive industry. Consequently, increasing amounts of CeO2 NPs are expected to enter the environment where their fate in and potential impacts are unknown. In this paper we describe the fate and effects of CeO2 NPs of three different sizes (14, 20, and 29 nm) in aquatic toxicity tests. In each standard test medium (pH 7.4) the CeO2 nanoparticles aggregated (mean aggregate size approximately 400 nm). Four test organisms covering three different trophic levels were investigated, i.e., the unicellular green alga Pseudokirchneriella subcapitata, two crustaceans: Daphnia magna and Thamnocephalus platyurus, and embryos of Danio rerio. No acute toxicity was observed for the two crustaceans and D. rerio embryos, up to test concentrations of 1000, 5000, and 200 mg/L, respectively. In contrast, significant chronic toxicity to P. subcapitata with 10% effect concentrations (EC10s) between 2.6 and 5.4 mg/L was observed. Food shortage resulted in chronic toxicity to D. magna, for wich EC10s of > or = 8.8 and < or = 20.0 mg/L were established. Chronic toxicity was found to increase with decreasing nominal particle diameter and the difference in toxicity could be explained by the difference in surface area. Using the data set, PNEC(aquatic)S > or = 0.052 and < or = 0.108 mg/L were derived. Further experiments were performed to explain the observed toxicity to the most sensitive organism, i.e., P. subcapitata. Toxicity could not be related to a direct effect of dissolved Ce or CeO2 NP uptake or adsorption, nor to an indirect effect of nutrient depletion (by sorption to NPs) or physical light restriction (through shading by the NPs). However, observed clustering of NPs around algal cells may locally cause a direct or indirect effect.

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To date, (eco)toxicological information on industrial nanoparticles is very limited. In the present study, the hypothesis that the ecotoxicity of nanoparticles (NPs) is related to their surface area and not to their mass was tested using a freshwater green algal species. Particle diameter and morphology were assessed using light scattering and electron microscopy techniques. To assess the toxicity of silica (SiO2) nanoparticles, the growth inhibition of the alga Pseudokirchneriella subcapitata when exposed to stable silica suspensions was monitored. Commercial LUDOX suspensions of nanoparticles with 12.5 and 27.0 nm diameter were found to be toxic, with 72-h 20% effect concentrations for growth rate (E(r)C20) values +/- standard deviation (n = 5) of 20.0 +/- 5.0 and 28.8 +/- 3.2 mg/L, respectively. The toxicity was attributable to the solid nanospheres, because no aggregation was observed and dissolution of the nanoparticles was negligible. When expressing the concentration as a surface area, the difference in toxicity was not significant. In the latter case, 72-h E(r)C20 values +/- standard deviation (n = 5) were 4.7 +/- 1.2 and 3.9 +/- 0.4 m2/L. Silica bulk material was found to be nontoxic up to 1 g/L. In an additional experiment with 100 mg/L of 12.5 and 27.0 nm SiO2 NPs, the interaction between the nanoparticles and algal cells was studied using transmission electron microscopy. Although the particles clearly adhered to the outer cell surface, no evidence was found for particle uptake.

We determine the optical properties of PbS/CdS core/shell QDs, addressing the energy and the oscillator strength of the first exciton transition and the intrinsic absorption coefficient at short wavelengths. It follows that the intrinsic absorption coefficient at wavelengths of 350 and 400 nm agrees with theoretical numbers predicted using the Maxwell–Garnett model. Moreover, close correspondence is demonstrated between the energy and the oscillator strength of the first exciton transition of PbS/CdS core/shell and PbS QDs with a similar core size. This provides a straightforward way to estimate the PbS core diameter in PbS/CdS core/shell quantum dots by means of the PbS sizing curve, and it indicates that PbS/CdS QDs exhibit a type 1 band alignment.

20The influence of pH (6.0-9.0), natural organic matter (NOM) (0-10 mgC/L) and ionic 21 strength (IS) (1.7-40 mM) on 14 nm CeO 2 NP aggregation and ecotoxicity towards the alga 22