Algal extracellular polymeric substance compositions drive the binding characteristics, affinity, and phytotoxicity of graphene oxide in water.

ABSTRACT

Graphene oxide (GO, a popular 2D nanomaterial) poses great potential in water treatment arousing considerable attention regarding its fate and risk in aquatic environments. Extracellular polymeric substances (EPS) exist widely in water and play critical roles in biogeochemical processes. However, the influences of complex EPS fractions on the fate and risk of GO remain unknown in water. This study integrates fluorescence excitation-emission matrix-parallel factor, two-dimensional correlation spectroscopy, and biolayer interferometry studies on the binding characteristics and affinity between EPS fractions and GO. The results revealed the preferential binding of fluorescent aromatic protein-like component, fulvic-like component, and non-fluorescent polysaccharide in soluble EPS (S-EPS) and bound EPS (B-EPS) on GO via π-π stacking and electrostatic interaction that contributed to a higher adsorption capacity of S-EPS on GO and weaker affinity than of B-EPS. Moreover, the EPS fractions drive the morphological and structural alterations, and the attenuated colloid stability of GO in water. Notably, GO-EPS induced stronger phytotoxicity (e.g., photosynthetic damage, and membrane lipid remodeling) compared to pristine GO. Metabolic and functional lipid analysis further elucidated the regulation of amino acid, carbohydrate, and lipid metabolism contributed to the persistent phytotoxicity. This work provides insights into the roles and mechanisms of EPS fractions composition in regulating the environmental fate and risk of GO in natural water.