Evaluation of the potential hazard of lanthanides to freshwater microcrustaceans

The use of lanthanides in different sectors of industry has significantly increased during the last decades. Although the "anthropogenic" anomalies of lanthanides in the soils, surface and ground waters have already been registered, the ecotoxicological effects of these elements and their fate in the environment are still insufficiently investigated. In this study acute and long-term toxicity of selected lanthanides (La, Ce, Pr, Nd and Gd) nitrates to freshwater crustaceans Daphnia magna, Thamnocephalus platyurus and Heterocypris incongruens were studied and critically evaluated. The data obtained show that (i) due to the methodical nuances the acute toxicity data of lanthanides are not reliable and have doubtful scientific value even for preliminary toxicity screening and thus should not be used for risk assessment; (ii) toxicity of lanthanides in the 21-day D. magna reproduction test was high whereas the mortality of parent daphnids was more sensitive endpoint than reproduction; (iii) the long-term LC50 values for lanthanides varied from 0.3 to 0.5 mg Ln/L and the differences between individual Ln were not statistically significant. All in all, the results of this study allow us to conclude that the environmental risk assessment of lanthanides should be performed only using long-term toxicity tests. In the environmental risk assessment, lanthanides may be considered as a uniform group of elements with additive mode of action until future investigations will not reveal differences in the ecotoxicity mechanisms of these elements.