The broad application of titanium dioxide nanoparticles in many consumer products has resulted in the release of substantial amounts into aquatic system, which serve as the terminal sink for nanomaterials. These titanium dioxide nanoparticles may induce some unexpected toxic effects to aquatic organisms such as microalgae. This study was carried out to evaluate the toxicity of limited nitrogen and titanium dioxide nanoparticles to the microalgae Chlorella vulgaris. The nanoparticles were prepared in Organisation for Economic Cooperation and Development (OECD) algal test medium and also the nitrogen concentration in the algal test medium was adjusted to match limited environmental nitrogen level. The growth, biomass production, biochemical composition (Carbohydrate and protein content), and antioxidant response (Glutathione-s-transferase, peroxidase, and lipid peroxidation) of the algae were monitored over a 96h period. The results showed that limited nitrogen (2.8 × 10-6 M) decrease growth, biomass (dry weight, cell counts, chlorophyll content), carbohydrate content, and increase protein content, antioxidant enzyme activity and lipid peroxidation (malondialdehyde content) in the alga. Titanium dioxide nanoparicle treatments (0.2mg/L, 8mg/L, 16mg/L and 32mg/L) decrease growth, biomass, carbohydrate content and increase glutathione-s-transferase activity. The combination of limited nitrogen with titanium dioxide nanoparticle decrease growth, dry weight, chlorophyll content, and carbohydrate content of the alga. This result suggests that limited nitrogen and titanium dioxide nanoparticle treatments affects growth, biomass production, biochemical composition, induces oxidative stress and also induces the oxidation of lipids while titanium dioxide nanoparticle combined with limited nitrogen affect growth, biomass, and carbohydrate content of Chlorella vulgaris under white fluorescent light.
1.1 Background to the Study
Microalgae are a very important component of the aquatic ecosystem; they are a group of fast growing unicellular or simple multicellular microorganisms that have the ability to fix CO2 while capturing solar energy with efficiency 10 to 50 times greater than that of terrestrial plants (Wang et al., 2008). They also have higher biomass production compared to energy crops (Wang et al., 2008).