Hierarchical Environmental Exposure Transforms Zeolitic Imidazolate Framework-8 and Increases Toxicity in <i>Daphnia magna</i>.
basic_science · Level V
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- Record sourced from PubMed, PMID 42188981.
- Also identified by DOI 10.1021/acsnano.6c01107.
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Abstract
Metal-organic frameworks (MOFs) are increasingly deployed in environmental technologies, yet their fate and hazard under realistic multistep exposure scenarios remain poorly constrained. Here, we track hierarchical transformations of nanoscale ZIF-8 (Zeolitic Imidazolate Framework-8) across an exposure cascade spanning atmospheric aging (air and reactive gases O<sub>3</sub>/NO<sub>2</sub>), aqueous aging in environmentally and biologically relevant media, and ingestion by the freshwater crustacean <i>Daphnia magna</i>. Synchrotron Zn K-edge X-ray absorption spectroscopy (XAS), micro-X-ray fluorescence (μ-XRF), X-ray photoelectron spectroscopy (XPS), and electron microscopy show that gas-phase exposure produces only minor surface perturbations, whereas aqueous contact drives pronounced medium-dependent restructuring, including nitrogen depletion and oxygen enrichment at the surface and time-resolved dissolved Zn release with chemistry-imposed plateaus. In vivo, Zn speciation diverges from the pristine Zn-N fingerprint; an unexposed endogenous Zn baseline and linear combination fitting (LCF) indicate a mixture of endogenous Zn with transformed Zn pools dominated by O/P/S-type coordination environments. Acute ecotoxicity assay demonstrates strong concentration dependence (48 h immobilization EC<sub>50</sub> ≈0.5 μg mL<sup>-1</sup>), and chronic exposure at 0.10 μg mL<sup>-1</sup> reduces cumulative brood production with increased adult mortality over 24 days. Mechanistically, fractionated toxicity assays show that washed aged particles/precipitates and whole aged suspensions are more potent than particle-free filtrates, indicating that particle-associated transformed Zn pools contribute substantially beyond dissolved Zn alone. Together, these results show that ZIF-8 risk emerges from its sequential transformation trajectory rather than its pristine state, motivating tiered aging protocols coupled to in vivo speciation and fractionated hazard testing for MOF safety assessment.