Fate and Effects of CeO₂ Nanoparticles in Aquatic Ecotoxicity Tests

Abstract

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.

A method for determination of retention of silver and cerium oxide manufactured nanoparticles in soils

“…The higher dissolution of Ag MNP relative to CeO 2 MNP in soils corresponds with observations in aquatic environments, [14,15] which suggest that whereas Ag MNP are retained more than CeO 2 MNP in soils, Ag MNP are less persistent, because they are easily oxidised. [43] Future research should be directed towards examining the influence of MNP coatings that may explain the lower partitioning of CeO 2 in soils, examining retention behaviour of Ag and CeO 2 MNP over a wider concentration range and developing models to predict the mobility of Ag and CeO 2 MNP in soils through an examination of retention behaviour in soils with a wider set of physicochemical characteristics.…”

“…[1] The catalytic properties of CeO 2 MNP are also used extensively and they are a common additive in diesel fuels. [1] The potential toxic properties of Ag and CeO 2 MNP towards aquatic [14,15] and in the case of Ag MNP [16] also to terrestrial organisms have been demonstrated. Toxic effects of Ag MNP have been related to cell membrane damage, to oxidative stress, or to interactions of Ag I ions with proteins and enzymes, [17] whereas both cytotoxic oxidative stress due to a reduction of Ce IV to Ce III within CeO 2 MNP [18] as well as a cytoprotective effect due to reduction of reactive oxygen species [19] have been observed in toxicity tests with CeO 2 MNP.…”

Ecotoxicity test methods for engineered nanomaterials: Practical experiences and recommendations from the bench

“…Measurements should be taken in addition to simply monitoring the mass concentration. For example, particle size distribution and particle number in the test media may need to be monitored to aid data interpretation or simply to give the researcher the option of plotting the data against a dose metric other than concentration [19][20][21]. Concerns have been expressed about when and how to change test media during a test.…”

Effect of particle size onin vitrocytotoxicity of titania and alumina nanoparticles

“…Results showed that proliferation and metabolism decreased with increasing equivalent surface area. Van Hoecke et al [42] observed a similar relationship between increasing NP surface area and a decrease in the reproduction rate of D. magna. Possible reasons for why NPs with larger equivalent surface area (small particles) may lead to more pronounced toxic effects may be a greater capacity to generate ROS and more nutrient depletion relative to smaller equivalent surface area particles (large particles).…”