Abstract
Despite the increasing use of rare earth elements (REEs) and oxides (REOs) in various technologies, the information on their ecotoxicological hazard is scarce. Here, the effects of La3+, Ce3+, Pr3+, Nd3+, Gd3+, CeO2, and eight doped REOs to marine bacteria Vibrio fischeri and freshwater protozoa Tetrahymena thermophila were studied in parallel with REO dopant metals (Co2+, Fe3+, Mn2+, Ni2+, Sr2+). The highest concentrations of REOs tested were 100 mg/L with protozoa in deionized water and 500 mg/L with bacteria in 2% NaCl. Although (i) most REOs produced reactive oxygen species; (ii) all studied soluble REEs were toxic to bacteria (half-effective concentration, EC50 3.5–21 mg metal/L; minimal bactericidal concentration, MBC 6.3–63 mg/L) and to protozoa (EC50 28–42 mg/L); and (iii) also some dopant metals (Ni2+, Fe3+) proved toxic (EC50 ≤ 3 mg/L), no toxicity of REOs to protozoa (EC50 > 100 mg/L) and bacteria (EC50 > 500 mg/L; MBC > 500 mg/L) was observed except for La2NiO4 (MBC 25 mg/L). According to kinetics of V. fischeri bioluminescence, the toxicity of REEs was triggered by disturbing cellular membrane integrity. Fortunately, as REEs and REOs are currently produced in moderate amounts and form in the environment insoluble salts and/or oxides, they apparently present no harm to aquatic bacteria and protozoa.
Highlights
Uniform group of metals, lanthanides (La–Lu), form together with yttrium (Y) and scandium (Sc) the group of rare earth elements (REEs)
The hydrodynamic size and the ζ-potential of particles were characterized in two media: deionized water (DI) that was used as a test medium for protozoan viability assay and 2% NaCl that was a test medium for marine bacteria Vibrio fischeri
Given the increased use of REEs and Rare Earth Oxide (REO) worldwide, we studied the toxicity of a series of rare earth elements and oxides to marine bacteria Vibrio fischeri and freshwater protozoa
Summary
Uniform group of metals, lanthanides (La–Lu), form together with yttrium (Y) and scandium (Sc) the group of REEs. REEs, in particular REOs, are increasingly used in many fields, e.g., catalysis, electronics, wind power generators, glass polishing and ceramics, metallurgical additives and alloys, high strength magnets, fuel cells, gas separation membranes, and fuel additives [1,2,3]. The most rapid increase of REEs production is expected for neodymium (Nd) and dysprosium (Dy), as they are used in magnets of wind turbines and electric/hybrid cars [4,5]. Some REEs, such as gadolinium (Gd), are used in health-related applications: in particular, Gd chelates are used as contrast agents for magnetic resonance imaging [10] and may reach the environment. REEs are considered of average supply risk, low environmental implications and low-to-medium vulnerability to supply restrictions, and currently China is the leading producer and trader of REEs [3,13]
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