Toxicity of lanthanide coagulants assessed using four in vitro bioassays

Rare earth element (REE) coagulants are prime contenders in wastewater treatment plants to remove phosphorus; unlike typical coagulants, they are not affected by pH. However, the use of REEs in wastewater treatment could mean increased human exposure to lanthanides (Ln) through wastewater effluent discharge to the environment or through water reuse. Information on the toxicity of lanthanides is scarce and, where available, there are conflicting views. Using in vitro bioassays, we assessed lanthanide toxicity by evaluating four relevant endpoints: the change in mitochondrial membrane potential (Delta psi m), intracellular adenosine triphosphate (I-ATP), genotoxicity, and cell viability. At less than 5000 mu mol-Ln(3+)/L, lanthanides increased the Delta psi m, while above 5000 mu mol-Ln(3+)/L, the Delta psi m level plummeted. The measure of I-ATP indicated constant levels of ATP up to 250 mu mol-Ln(3+)/L, above which the I-ATP decreased steadily; the concentration of La, Ce, Gd, and Lu that triggered half of the cells to become ATP-inactive is 794, 1505, 1488, 1115 mu mol-Ln(3+)/L, respectively. Although La and Lu accelerated cell death in shorter studies (24 h), chronic studies using three cell growth cycles showed cell recovery. Lanthanides exhibited antagonistic toxicity at less than 1000 mu mol-Ln(3+)/L. However, the introduction of heavy REEs in a solution amplified lanthanide toxicity. Tested lanthanides appear to pose little risk, which could pave the way for lanthanide application in wastewater treatment. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Rare earth element (REE) coagulants are effective in removing phosphorus in wastewater treatment plants, but their use may increase human exposure to lanthanides. Information on lanthanide toxicity is limited and sometimes conflicting. Tested lanthanides show relatively low risk, indicating potential application in wastewater treatment.