title: Potency of (doped) rare earth oxide particles and their constituent metals to inhibit algal growth and induce direct toxic effects.
abstract: Use of rare earth elements (REEs) has increased rapidly in recent decades due to technological advances. It has been accompanied by recurring rare earth element anomalies in water bodies. In this work we (i) studied the effects of eight novel doped and one non-doped rare earth oxide (REO) particles (aimed to be used in solid oxide fuel cells and gas separation membranes) on algae, (ii) quantified the individual adverse effects of the elements that constitute the (doped) REO particles and (iii) attempted to find a discernible pattern to relate REO particle physicochemical characteristics to algal growth inhibitory properties. Green algae Raphidocelis subcapitata (formerly Pseudokirchneriella subcapitata) were used as a test species in two different formats: a standard OECD201 algal growth inhibition assay and the algal viability assay (a 'spot test') that avoids nutrient removal effects. In the 24h 'spot' test that demonstrated direct toxicity, algae were not viable at REE concentrations above 1mgmetal/L. 72-hour algal growth inhibition EC50values for four REE salts (Ce, Gd, La, Pr) were between 1.2 and 1.4mg/L, whereas the EC50for REO particles ranged from 1 to 98mg/L. The growth inhibition of REEs was presumably the result of nutrient sequestration from the algal growth medium. The adverse effects of REO particles were at least in part due to the entrapment of algae within particle agglomerates. Adverse effects due to the dissolution of constituent elements from (doped) REO particles and the size or specific surface area of particles were excluded, except for La2NiO4. However, the structure of the particles and/or the varying effects of oxide composition might have played a role in the observed effects. As the production rates of these REO particles are negligible compared to other forms of REEs, there is presumably no acute risk for aquatic unicellular algae.
authors.affiliation: Laboratory of Environmental Toxicology, National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, Tallinn 12618, Estonia; Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005 Tartu, Estonia. Electronic address: elise.joonas@kbfi.ee.
authors.forename: Elise
authors.initials: E
authors.lastname: Joonas
authors.affiliation: Laboratory of Environmental Toxicology, National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, Tallinn 12618, Estonia.
authors.forename: Villem
authors.initials: V
authors.lastname: Aruoja
authors.affiliation: Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005 Tartu, Estonia.
authors.forename: Kalle
authors.initials: K
authors.lastname: Olli
authors.affiliation: Ceramic Powder Technology AS, Kvenildmyra 6, 7093 Tiller, Norway.
authors.forename: Guttorm
authors.initials: G
authors.lastname: Syvertsen-Wiig
authors.affiliation: Laboratory of Environmental Toxicology, National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, Tallinn 12618, Estonia.
authors.forename: Heiki
authors.initials: H
authors.lastname: Vija
authors.affiliation: Laboratory of Environmental Toxicology, National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, Tallinn 12618, Estonia; Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia.
authors.forename: Anne
authors.initials: A
authors.lastname: Kahru
mesh_terms: D000460:Chlorophyta / Q000187:drug effects* / Q000254:growth & development; D008674:Metals, Rare Earth / Q000633:toxicity*; D010087:Oxides / Q000633:toxicity*
chemical_list: D008674:Metals, Rare Earth; D010087:Oxides
keywords: Agglomeration; Hazard evaluation; Lanthanides; Nanoparticles; Phytoplankton