Toxicity Effects and Mechanisms of Graphdiyne towards Freshwater Microalgae Scenedesmus obliquus

Graphdiyne (GDY), an emerging 2D carbon nanomaterial, holds promise yet remains unexplored for environmental hazards. Herein, we investigated the toxicity effects and mechanisms of GDY towards the freshwater microalga Scenedesmus obliquus at environmentally relevant concentrations. The results revealed that 1 mg/L of GDY inhibited the growth of the algae and significantly induced a decrease in photosynthetic pigments. Exposure to 0.1 and 1 mg/L of GDY led to a reduction in cell membrane permeability and induced intracellular oxidative stress in the algae. Further, 1 mg/L of GDY caused oxidative damage to the algal cells. Molecular modeling indicated that GDY could directly affect the stability of dsDNA fragment. Transcriptome analysis showed that GDY at 1 mg/L influenced the expression of 2216 genes, with the glycerolipid metabolism pathway being enriched significantly. Metabolome analysis identified 129 differentially expressed metabolites (DEMs) in the algae exposed to 1 mg/L of GDY, revealing three significantly disrupted pathways: glycerophospholipid metabolism, pentose phosphate pathway, and flavonoid biosynthesis. The integrated transcriptome and metabolome analysis suggested that GDY exposure downregulated the level of a lysophosphatidylcholine species (LPC 18:3) by inhibiting the expression of genes related to FMN binding molecular functions. Simultaneously, the algae responded to GDY exposure by upregulating genes involved in the biological process of carbohydrate metabolic process and the molecular function of hydrolase activity, as well as increasing the levels of DEMs, specifically a lysophosphatidic acid species (LPA 16:4). This study elucidates the stress mechanisms induced by GDY in aquatic organisms and emphasizes the importance of monitoring its acute biological effects.