Nitrogen Forms and Concentration Influence the Impact of Titanium dioxide Nanoparticles on the Biomass and Antioxidant Enzyme Activities of Microcystis aeruginosa

Abstract The popularity of Nanoparticles (NPs) have led to their wide production, applications and subsequently released into the aquatic environment in some instances. In the aquatic ecosystem, these NPs affect different populations of photosynthesizing organisms, such as cyanobacteria. The effect of Microcystis aeruginosa exposed to titanium dioxide nanoparticles (TiO2-NPs, 48 mg l− 1), in combination of low and high concentrations of urea (0.04 mM) and nitrate (9 Mm) was assessed. Microcystins (MCs) production and release were monitored in the cyanobacterium. Results showed that high urea (9 mM), combined with TiO2-NPs, inhibited the growth, pigment and malondialdehyde (MDA) content by 82%, 63% and 47% respectively. But 40.7% and 67.7% increase in the concentration of Reactive Oxygen Species (ROS) and glutathione S-transferase (GST) activity was observed in M. aeruginosa respectively. Similarly, low nitrate (0.04 mM) combined with TiO2-NPs inhibited growth by 40.3% and GST activity by 36.3%, but stimulated pigment production and ROS concentration in M. aeruginosa. A response suggests that the high urea combined with TiO2 –NPs and high nitrate combined with TiO2 –NPs exposure induced oxidative stress in the cyanobacterium. The peroxidase (POD) activity of M. aeruginosa decreased by 17.7% with increasing urea concentrations. Our findings suggest TiO2-NPs and nutrients (urea and nitrate) concentration may adversely impact cyanobacterial development and antioxidant defense enzymes. Although the effect of nitrate concentration on M. aeruginosa was observed to be subsidiary.