Interactions between extracellular polymeric substances and engineered nanoparticles in aquatic systems and their environmental effects: a comprehensive review

Abstract

Extracellular polymeric substances (EPS), which are secreted during the growth and metabolism of microorganisms, can be adsorbed onto the surface of nanoparticles (NPs) to form an EPS corona. The presence of EPS corona can significantly alter the environmental processes and toxicity of NPs in aquatic systems. Firstly, this review thoroughly summarizes the interactions between EPS and engineered NPs, including the major interaction mechanisms and their corresponding representative interaction modes, i.e., electrostatic attraction/repulsion, hydrophobic interaction, chemical bonding, hydrogen bonding, and cation bridging. Currently, classical kinetic and thermodynamic models are considered to be suitable for describing the adsorption of EPS on most NPs. Next, the main environmental processes of NPs influenced by EPS, including their dispersion/aggregation, chemical transformation, and sorption capability, are discussed. Due to the alteration of the above-mentioned environmental processes of NPs, EPS can influence the toxicity effects of NPs on aquatic organisms. The influencing mechanisms of two types of EPS (soluble EPS, S-EPS and bound EPS, B-EPS) on the toxicity of NPs are separately summarized. It is concluded that both types of EPS play their respective roles in influencing the toxicity of NPs. Finally, the subsequent change of microbial EPS secretion influenced by NPs is addressed. As an external stress, NPs exposure has been proven to affect the amount and composition of EPS secretion. However, the mechanism of EPS-NPs interactions needs to be further investigated. We suggest that the vital role of EPS on the transfer of NPs through trophic levels in aquatic systems under long-term exposure should be further examined. Moreover, the correlation between the changes in EPS secretion and NPs toxicity is still unknown. We suggest that advanced in situ analytical techniques and molecular biological technologies should be applied to investigate the effect of EPS on the environmental behavior of NPs. The information provided in this study will enhance our understanding of the crucial role of EPS in determining the biological effects of NPs and contribute to a better assessment of the ecological risks of NPs in aquatic systems.