Herbicides constitute a serious environmental problem because they can affect nontarget organisms. The toxicity of these chemicals depends on their interaction with prevailing environmental conditions. In this study, the effect of atrazine (ATR) (0.05, 0.5 and 5.0 mg L -1 ) at different nitrogen concentrations (1.8 9 10 -4 and 1.8 9 10 -5 M) on the growth, morphological variation, biomass production and antioxidant enzyme activities of the freshwater microalga Scenedesmus quadricauda was investigated. Compared with the control, growth rate, dry weight and cell density were lower under limited nitrogen with or without ATR exposure. The proportion of multicelled coenobial structures was generally higher in the control and ATR treatments with replete (1.8 9 10 -4 M) nitrogen than that under limited nitrogen. Catalase and peroxidase activities decreased under nitrogen limitation and atrazine exposure. In conclusion, our results revealed that nitrogen levels influence the toxicity of atrazine to S. quadricauda and possibly other algae in aquatic ecosystems.
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 (TiO 2 -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 TiO 2 -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 TiO 2 -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 TiO 2 -NPs and high nitrate combined with TiO 2 -NPs exposure induced oxidative stress in the cyanobacterium. The peroxidase (POD) activity of M. aeruginosa decreased by 17.7% with increasing urea concentrations. Our ndings suggest TiO 2 -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.
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.
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