Causes and mechanisms on the toxicity of layered double hydroxide (LDH) to green algae Scenedesmus quadricauda

Highlights: • The growth of S. quadricauda was significantly inhibited by LDH. • The light and dark 24 h EC50s for algae by LDH was 10 and 25 mg L⁻¹, respectively. • LDH induced changes in algal photosynthesis, oxidative stress and lipid peroxidation. • Shading effect, agglomeration and oxidative stress mainly contributed such toxicity. Layered double hydroxides (LDHs) are widely used nanomaterials in industrial catalysis, pharmaceuticals, and environmental remediation, and may pose potential negative effects in the aquatic environment. However, little information is available on their toxicity to aquatic organisms. In this study, toxicity of LDH to a typical freshwater green algae Scenedesmus quadricauda was systematically investigated and the underlying mechanisms were elucidated. The growth of S. quadricauda was significantly inhibited by LDH at 72 h with a half maximal effective concentration (EC₅₀) and lowest observed effect concentration (LOEC) of 10.0 and 1.5 mg L⁻¹, respectively. Shading effect was observed, and the photosynthetic activity and cellular chlorophyll production were also severely suppressed by LDH. LDH also enhanced the reactive oxygen species production from S. quadricauda and lipid peroxidation in algal cells. Such algal toxicity of LDH might be mainly induced by the shading effect, agglomeration and physical interactions, and oxidative stress. The agglomeration and physical interactions contributed more to the algal toxicity at 72 h-EC₅₀ LDH concentrations. The results from the present study provided new insights and a better understanding of the environmental behavior and adverse effects of LDHs in the surface waters.