Behaviour of ceria nanoparticles in standardized test media – influence on the results of ecotoxicological tests

The main objectives of this work were to establish the behaviour of a ceria nanopowder in different ecotoxicological media commonly used in standardized aquatic ecotoxicity tests and consequently to assess the acute and chronic ecotoxicity in two micro-invertebrates: Daphnia magna and Ceriodaphnia dubia and in a freshwater green algae: Pseudokirchneriella subcapitata. Different approaches to disperse the ceria nanoparticles (i.e. stirring, use of probe sonication, addition of humic acids) were tested and the influence on the biological endpoints was investigated. Despite the agglomeration phenomena observed in all the tested media, the results obtained indicated higher stability in the lower ionic strength media with addition of humic acid (2 mg.L−1 TOC). No acute toxicity were observed with D. magna, whatever the dispersal method performed and the nCeO2 concentration tested (up to 1000 mg.L−1), as no acute toxicity was recorded with C. dubia following exposure to the stirring suspensions. On contrary, acute toxicity was recorded in C. dubia with EC50 values comprise between 11.9 and 25.3 mg.L−1 using the probe sonicated suspension with or without humic acids addition. Significant chronic effect on the reproduction capability was also recorded in C. dubia. The estimated EC10 values were comprised between 2.1 and 2.9 mg.L−1. Focusing on P. subcapitata, despite the different agglomerate size recorded in the tested media at the end of the exposure periods, results obtained were similar. Adverse effect on algal growth around 5 mg.L−1 were reported (mean EC10 = 4 ± 1.8 mg.L−1). Those results suggested the needed for standardized testing protocol concerning the aqueous media used or the sample preparation for laboratory testing.