Effects of environmental factors on the growth and microcystin production of Microcystis aeruginosa under TiO2 nanoparticles stress

Abstract Due to the growing use and release of nanomaterials, their toxic impacts on aquatic ecosystems have drawn widespread attention in recent years. In this study, we exposed Microcystis aeruginosa to 5 mg/L titanium dioxide nanoparticles (nTiO2) under different culture conditions (pH 6, 7, 8, 9; 20 °C, 25 °C, 30 °C). The results showed that algae had the worst growth status with lowest biomass, lowest photosynthetic activity and highest reactive oxygen species (ROS) generation under 5 mg/L nTiO2 at pH 6 and 20 °C. Images by scanning electron microscopy (SEM) revealed that nTiO2 hindered light absorption by algal cells by wrapping the algal surface, which led to obvious cell surface deformation at pH 6 or 20 °C. In addition, microcystin-LR (MC-LR) production increased as temperature or pH decreased when exposed to nTiO2 at 5 mg/L, demonstrating that falling pH or temperature enhanced the adverse effects toward algal cells under nTiO2 stress and the potential risk of algae to the environment.