Interactions of metal oxide nanoparticles with extracellular polymeric substances (EPS) of algal aggregates in an eutrophic ecosystem

Nanoparticle binding with organic ligands in natural waters is important to understand their environmental behavior and fate. In this study, the interaction of two metal oxide nanoparticles (nano-CuO and nano-Fe3O4) with extracellular polymeric substances (EPS) from algal aggregates was studied through using fluorescence emission-excitation matrix (EEM) quenching titration combined with parallel factor (PARAFAC) analysis. Spectroscopy analysis detected two protein-like peaks in the loosely bound EPS (LB–EPS) fraction, while both protein-, fulvic- and humic-like peaks can be found in the tightly bound EPS (TB–EPS) fraction. PARAFAC analysis identified three independent fluorescence components, including one tryptophan-, one tyrosine- and one humic-like component, from 68 original EEM spectra. A quenching experiment showed that humic-like components in the TB–EPS fraction exhibited higher nanoparticle binding capacities (logKM > 6.23) than that in the LB–EPS fraction (logKM: 5.66), while the mobility of nano-Fe3O4 would be influenced by organic ligands in the TB–EPS fraction (logKM > 6.28). Based on the results, the toxicity of nanoparticles in the eutrophic waters would be higher than those in the oligotrophic ecosystems. This study facilitates a deeper understanding of the environmental behavior and fate of metal oxide nanoparticles in eutrophic aquatic ecosystems.