Assessment of the hazard of nine (doped) lanthanides-based ceramic oxides to four aquatic species.

The risk of environmental pollution with rare earth oxides rises in line with increasing application of these compounds in different sectors. However, data on potential environmental hazard of lanthanides is scarce and concerns mostly Ce and Gd. In this work, the aquatic toxicity of eight doped lanthanide-based ceramic oxides (Ce0.9Gd0.1O2, LaFeO3, Gd0.97CoO3, LaCoO3, (La0.5Sr0.5)0.99MnO3, Ce0.8Pr0.2O2, (La0.6Sr0.4)0.95CoO3, LaNiO4) and one non-doped oxide (CeO2) with primary size from 23 to 590nm were evaluated in four short-term laboratory assays with freshwater crustaceans and duckweeds. Results showed no acute toxicity (EC50>100mg/L) or very low acute toxicity for most studied oxides. Observed toxicity was probably due to bioavailable fraction of dopant metals (Ni and Co) but in the case of aquatic plants, decrease of nutrient availability (complexing of phosphorus by lanthanides) was also presumed. Studied oxides/metals accumulated in the aquatic plant tissue and in the gut of crustaceans and thus may be further transferred via the aquatic food chain. Accumulation of metals in the duckweed Lemna minor may be recommended as a cost-effective screening bioassay for assessment of potential hazard of poorly soluble oxides to aquatic ecosystems.