Sunlight regulates the specific interaction and mechanism of graphene oxide in the photosynthesis-metabolism of Chlorella vulgaris in natural surface water.

The photosensitive sp and hyperactive sp domains of 2D-film-like graphene oxide (GO) play critical roles in biogeochemical processes. However, the underlying toxicity mechanism of the specific effects of GO on Chlorella vulgaris (C. vulgaris) remains unknown. In this study, we combined macroscopic and microscopic approaches to systematically investigate the effects of GO on C. vulgaris. Visual batch experiments and colloidal property analysis revealed that GO undergoes aggregation-sedimentation in natural surface water, leading to the physical entrapment of C. vulgaris. A series of advanced characterization techniques further demonstrated that the aggregation and photo-transformation of GO mitigate direct physical damage to algal cells, while GO coating induces oxidative stress and activates the antioxidant enzyme system. Through integrated regular and metabolic analysis, we found that GO reduces sunlight-induced interference with carbon fixation metabolism in photosynthetic organisms but enhances the sunlight-regulated intensity of the cofactor and vitamin metabolism pathways. This study provides new insights into the roles and mechanisms of the unique physicochemical properties of GO in regulating its environmental risk in aqueous ecosystems.