Functionalization-dependent toxicity of MIL-101 metal-organic frameworks to phytoplankton Chlamydomonas reinhardtii

The MIL-101 series metal-organic frameworks have attracted significant attention in water remediation, leading to their inevitable release into the aquatic environments. However, research on the toxic effects of MIL-101 on aquatic organisms is in its infancy, and the responses of freshwater algae to MIL-101 and its amino-functionalized counterpart, MIL-101-NH₂, are poorly understood. In this study, the freshwater green algae Chlamydomonas reinhardtii (C. reinhardtii) were exposed to varying concentrations of MIL-101 or MIL-101-NH₂ (0.1-50 mg/L) for 7 d The impacts of MIL-101 and MIL-101-NH₂ on algal viability and photosynthesis activity were systematically evaluated. Additionally, non-targeted metabolomics was employed to obtain an overview of the physiological status of the algae under MIL-101/MIL-101-NH₂ exposure. Exposure to 50 mg/L of MIL-101 or MIL-101-NH₂ resulted in reduced algal viability, suppressed photosynthetic activity, and significant metabolic reprogramming. In contrast, low concentrations (0.1 mg/L) of either MIL-101 or MIL-101-NH₂ did not induce any detectable physiological alterations. The observed algal toxicity was primarily due to the direct physical interactions with the particles rather than release of metal ions. The divergent metabolic impacts caused by MIL-101/MIL-101-NH₂ suggested the contribution of functionalization to MOF's biological outcomes. These findings provide valuable insights into the ecological impacts of MOFs in aquatic ecosystems and reveal the importance of functionalization in MOFs-associated environmental impacts.