title: Freshwater dispersion stability of PAA-stabilised cerium oxide nanoparticles and toxicity towards Pseudokirchneriella subcapitata.
abstract: An aqueous dispersion of poly (acrylic acid)-stabilised cerium oxide (CeO₂) nanoparticles (PAA-CeO₂) was evaluated for its stability in a range of freshwater ecotoxicity media (MHRW, TG 201 and M7), with and without natural organic matter (NOM). In a 15 day dispersion stability study, PAA-CeO₂ did not undergo significant aggregation in any media type. Zeta potential varied between media types and was influenced by PAA-CeO₂ concentration, but remained constant over 15 days. NOM had no influence on PAA-CeO₂ aggregation or zeta potential. The ecotoxicity of the PAA-CeO₂ dispersion was investigated in 72 h algal growth inhibition tests using the freshwater microalgae Pseudokirchneriella subcapitata. PAA-CeO₂ EC₅₀ values for growth inhibition (GI; 0.024 mg/L) were 2-3 orders of magnitude lower than pristine CeO₂ EC₅₀ values reported in the literature. The concentration of dissolved cerium (Ce(3+)/Ce(4+)) in PAA-CeO₂ exposure suspensions was very low, ranging between 0.5 and 5.6 μg/L. Free PAA concentration in the exposure solutions (0.0096-0.0384 mg/L) was significantly lower than the EC10 growth inhibition (47.7 mg/L) value of pure PAA, indicating that free PAA did not contribute to the observed toxicity. Elemental analysis indicated that up to 38% of the total Cerium becomes directly associated with the algal cells during the 72 h exposure. TOF-SIMS analysis of algal cell wall compounds indicated three different modes of action, including a significant oxidative stress response to PAA-CeO₂ exposure. In contrast to pristine CeO₂ nanoparticles, which rapidly aggregate in standard ecotoxicity media, PAA-stabilised CeO₂ nanoparticles remain dispersed and available to water column species. Interaction of PAA with cell wall components, which could be responsible for the observed biomarker alterations, could not be excluded. This study indicates that the increased dispersion stability of PAA-CeO₂ leads to an increase in toxicity compared to pristine non-stabilised forms.
authors.affiliation: SINTEF Materials and Chemistry, Trondheim N-7465, Norway. Electronic address: andy.booth@sintef.no.
authors.forename: Andy
authors.initials: A
authors.lastname: Booth
authors.affiliation: SINTEF Materials and Chemistry, Trondheim N-7465, Norway.
authors.forename: Trond
authors.initials: T
authors.lastname: Størseth
authors.affiliation: BioTrix, Trondheim N-7022, Norway.
authors.forename: Dag
authors.initials: D
authors.lastname: Altin
authors.affiliation: German Federal Institute for Risk Assessment (BfR), Department of Product Safety, Berlin, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Fornara
authors.affiliation: German Federal Institute for Risk Assessment (BfR), Department of Product Safety, Berlin, Germany.
authors.forename: Anwar
authors.initials: A
authors.lastname: Ahniyaz
authors.affiliation: SP Chemistry, Materials and Surfaces, Drottning Kristinas vag 45, SE-11686 Stockholm, Sweden.
authors.forename: Harald
authors.initials: H
authors.lastname: Jungnickel
authors.affiliation: SP Chemistry, Materials and Surfaces, Drottning Kristinas vag 45, SE-11686 Stockholm, Sweden.
authors.forename: Peter
authors.initials: P
authors.lastname: Laux
authors.affiliation: SP Chemistry, Materials and Surfaces, Drottning Kristinas vag 45, SE-11686 Stockholm, Sweden.
authors.forename: Andreas
authors.initials: A
authors.lastname: Luch
authors.affiliation: SINTEF Materials and Chemistry, Trondheim N-7465, Norway.
authors.forename: Lisbet
authors.initials: L
authors.lastname: Sørensen
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D002563:Cerium / Q000737:chemistry / Q000633:toxicity*; D000460:Chlorophyta / Q000187:drug effects*; D005618:Fresh Water / Q000737:chemistry; D053758:Nanoparticles / Q000737:chemistry / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000633:toxicity*
chemical_list: D000180:Acrylic Resins; D014874:Water Pollutants, Chemical; D002563:Cerium; C006903:carbopol 940; C030583:ceric oxide
keywords: CeO(2); Dispersion stability; Ecotoxicity; Freshwater algae; Nanoparticles