Evaluation and Control of Environmental Microbial Toxicity of Microplastics

Abstract

This study aimed to clarify the effects of nanoplastics on microorganisms in aquatic environments and establish guidelines for controlling their toxicity. Positively charged polystyrene nanoparticles were used as model nanoplastics, and Escherichia coli at different growth stages (exponential and stationary phases) were employed as model microorganisms. Particle exposure experiments were conducted under various salt concentrations. Bacterial size, particle adhesion, cell membrane integrity, and colony-forming ability were evaluated using flow cytometry (FCM) and confocal laser scanning microscopy (CLSM). The results showed that under low-salinity conditions, nanoparticle adhesion increased, leading to significant cell membrane damage and reduced colony-forming ability. In contrast, under high-salinity conditions, particle adhesion and cytotoxicity were suppressed due to electrostatic screening effects. Cytotoxic effects caused by particle adhesion were more pronounced in exponentially growing cells than in stationary-phase cells. These findings demonstrate that not only exposure conditions but also the microbial growth state strongly influence the toxicity of nanoplastics toward microorganisms.

Graphical Abstract

Colony-forming ability as a function of NaCl concentration for E. coli after 0.5-h exposure to NaCl solutions (C_NaCl = 5, 25, 50, 100, 150, 300, and 600 mM) at 25°C.