Individual and combined cytotoxicity effects of positively charged polystyrene nanoplastics and ionic surfactants on budding yeast Saccharomyces cerevisiae

• Combined toxicity of nanoparticles (NPs) and anionic/cationic surfactants was studied. • Budding yeast cells and positively charged polystyrene NPs (pPS-NPs) were employed. • 115-nm pPS-NPs were more cytotoxic than 204-nm pNPs in the absence of surfactants. • Toxicity of pPS-NPs was reduced by adding anionic surfactants (counteracting effect). • Toxicity of pPS-NPs was enhanced by adding cationic surfactants (synergistic effect). It is of crucial importance to understand the impact of micro/nanoplastics contaminated with the other pollutants on microorganisms in the environment. In the present paper, we have investigated the individual and combined cytotoxicity effects of positively charged fluorescence-labeled polystyrene nanoparticles (pPS-NPs; 115 and 204 nm in diameter) and ionic surfactants [sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium chloride (C 12 TAC)] on budding yeast Saccharomyces cerevisiae after a short-time exposure (0.5 h) in a 5-mM NaCl aqueous solution. In the absence of surfactants, the smaller 115-nm pPS-NPs were more cytotoxic than the larger 204-nm pPS-NPs. In the absence of pPS-NPs, the cationic surfactant of C 12 TAC was more cytotoxic than the anionic surfactant of SDS, though these two ionic surfactants have the hydrophobic alkyl chains of the same length and the oppositely charged headgroups in the same magnitude. The addition of SDS decreased the number of pPS-NPs adhered on a negatively charged yeast cell to reduce the cytotoxicity, whereby the combined toxicity effect was considered as counteracting action. Although some addition of C 12 TAC hardly influenced the number of pPS-NPs adhered on a yeast cell, the synergistic cytotoxicity action of the pPS-NPs and C 12 TAC was observed.