Metabolomic analysis to understand the mechanism of TiCT (MXene) toxicity in Daphnia magna.

Due to their potential release into the environment, the ecotoxicity of TiCT (MXene) nanomaterials is a growing concern. Unfortunately, little is known about the toxic effects and mechanisms through which TiCT induces toxicity in aquatic organisms. The aim of this study is thus to investigate the toxic effects and mechanisms of Daphnia magna upon exposure to TiCT with different sheet sizes (100 nm [TiCT-100] and 500 nm [TiCT-500]) by employing conventional toxicology and metabolomics analysis. The results showed that exposure to both TiCT-100 and TiCT-500 at 10 μg/mL resulted in a significant accumulation of TiCT in D. magna, but no effects on the mortality or growth of D. magna were observed. However, the metabolomics results revealed that TiCT-100 and TiCT-500 induced significant changes in up to 265 and 191 differential metabolites in D. magna, respectively, of which 116 metabolites were common for both. TiCT-100-induced metabolites were mainly enriched in phospholipid, pyrimidine, tryptophan, and arginine metabolism, whereas TiCT-500-induced metabolites were mainly enriched in the glycerol-ester, tryptophan, and glyoxylate metabolism and the pentose phosphate pathway. These results indicated that the toxicity of TiCT to D. magna has a size-dependent effect at the metabolic level, and both sheet sizes of TiCT can lead to metabolic disturbances in D. magna by interfering with lipid and amino acid metabolism pathways.