Impact of algal extracellular polymeric substances on the environmental fate and risk of molybdenum disulfide in aqueous media.

Molybdenum disulfide (MoS) poses great potential in water treatment as a popular transition metal dichalcogenide, arousing considerable concern regarding its fates and risk in aquatic environments. This study revealed that the interplay with extracellular polymeric substances (EPS) of freshwater algae significantly changed the properties and toxicity of MoS to aquatic fish. The predominant binding of aromatic compounds, polysaccharides, and carboxyl-rich proteins in EPS on the 1T polymorph of MoS via hydrophilic effects and the preferential adsorption of carboxylic groups contributed to morphological alterations, structural disorders (band gap and phase alterations), and the attenuated aggregation of MoS in aqueous solutions. Electron charge transfer and n-π* interactions with EPS decreased the catalytic activity of MoS by inhibiting its capability of generating reactive intermediates. The dissolution of MoS slowed down after interacting with EPS (from 0.089 to 0.045 mg/L per day) owing to rapid initial oxidation (i.e., forming Mo-O bond) and carbon grafting. Notably, the morphological and structural alterations after EPS binding alleviated the toxicity (e.g., malformation and oxidative stress) of MoS to infantile zebrafish. Our findings provide insights into the environmental fate and risk of MoS by ubiquitous EPS in natural waters, serving as valuable information while developing water treatment processes accordingly.