The combined toxicity effect of nanoplastics and glyphosate on Microcystis aeruginosa growth

Highlights: • PS-NH₂ alleviated the inhibitory effect of glyphosate on M. aeruginosa growth. • PS-NH₂ displayed an excellent adsorption capacity for glyphosate. • Glyphosate induced more PS-NH₂ to adsorb on M. aeruginosa. Waste plastics can be degraded to nanoplastics (NPs, diameter < 1 μm) by natural forces. NPs not only directly affect aquatic organisms but also adsorb other pollutants, causing combined pollution. Glyphosate is one of the most widely used herbicides and is commonly monitored in freshwater systems. In this study, the effects of the combined toxicity of polystyrene cationic amino-modified nanoparticles (nPS-NH₂) and glyphosate on a blue-green alga, Microcystis aeruginosa, were investigated. Our results demonstrated that 5 mg/L glyphosate had a strong inhibitory effect on M. aeruginosa (the 96-h inhibitory rate was 27%), while 5 mg/L nPS-NH₂ had no apparent effect on the growth of M. aeruginosa. Interestingly, nPS-NH₂ combined with glyphosate showed antagonistic effects on the inhibition of algal growth because nPS-NH₂ displayed a strong adsorption capacity for glyphosate, which significantly alleviated the inhibitory effect of glyphosate on M. aeruginosa growth. However, the presence of glyphosate enhanced the stability of the dispersion system, which allowed more nPS-NH₂ to adsorb on the surface of M. aeruginosa and may result in greater enrichment of nPS-NH₂ in the food chain to show potential repercussions to human life. Our current study provides a new theoretical basis for the combined effects of NPs and pesticide pollution.