Ecotoxicity of ZnFeAl-Cl Layered Double Hydroxides toward Freshwater And Marine Algal Species: LDH Synthesis, Photosynthetic Pigment Alterations, and Physiological Stress Responses

Layered double hydroxides (LDHs) are widely used in industrial and environmental applications, raising concerns about their potential ecotoxicological effects in aquatic systems. The ZnFeAl-Cl LDH was synthesized via coprecipitation, yielding a brucite-like structure. Electron microscopy images revealed platelet-like particles composed of stacked nanosheets, and X-ray photoelectron spectroscopy confirmed the presence of Zn 2+, Fe 3+, and Al 3+ species. The acute toxicity of ZnFeAl-Cl LDH was evaluated using two microalgal species originating from different aquatic environments: the freshwater species Chlorella vulgaris (SAG:211–12) and the marine species Cyclotella cryptica (CC 1070). Growth inhibition, photosynthetic pigments, phenolic and anthocyanin content, and antioxidant enzyme activities were monitored following exposure to increasing LDH concentrations. ZnFeAl-Cl LDH-induced concentration-dependent growth inhibition in both species, with C. cryptica being more susceptible than C. vulgaris, showing a decline in cell density exceeding 50% by day 15. Microscopy observations indicated more pronounced morphological alterations in C. cryptica at higher concentrations, whereas C. vulgaris cells appeared comparatively less affected. Chlorophyll a/b content decreased with increasing LDH concentration in both algae, with more pronounced effects observed in C. cryptica . At 25 mg·L –1 ZnFeAl-Cl LDH, chlorophyll a/b inhibition reached 41% in C. cryptica, whereas the corresponding reduction was only 23% in C. vulgaris . Antioxidant enzyme responses also differed between species. SOD activity was markedly higher at 250 mg·L –1 in C. vulgaris than in C. cryptica (12.8 vs 0.4 unit·mg protein –1 ·min –1 ). CAT activity increased with increasing LDH concentration in both species, reaching 35.1 and 9.8 unit·g protein –1 ·min –1 in C. vulgaris and C. cryptica, respectively, at 250 mg·L –1 . Secondary antioxidant responses further highlighted species-specific behavior. In contrast, anthocyanin levels decreased steadily in both species with increasing LDH concentration.