Environmentally Relevant Concentrations of TiO 2 Nanoparticles Affected Cell Viability and Photosynthetic Yield in the Chlorophyceae Scenedesmus bijugus

The impact of nanoparticles (NPs) in phytoplankton is understudied, particularly with respect to the organism’s physiology and environmentally relevant concentrations. In the present research, we investigated the effects of titanium dioxide nanoparticles (nano-TiO 2 ) in the physiology of Scenedesmus bijugus , a freshwater cosmopolitan phytoplankter, exposed to concentrations ranging from 3.30 × 10 −9 mol L −1 (log −8.48) to 3.70 × 10 −7 mol L −1 (log −6.43), which includes environmentally relevant values. The nano-TiO 2 concentrations in the medium and in the cells were determined in experiments that lasted 96 h. Controlled environmental conditions were used throughout and a variety of endpoints were monitored. These included cell density, cell viability, chlorophyll a concentration, growth rates, maximum quantum yield of photosystem II (Φ M ), intracelular proteins and carbohydrates, and proteins:carbohydrates ratios. The results showed that cell viability was the most sensitive parameter for the detection of the nano-TiO 2 effects, being followed by Φ M . At the concentration of 3.90 × 10 −8 mol L −1 (log −7.40), there was an increase of nano-TiO 2 injured cells, and at 3.70 × 10 −7 mol L −1 (log −6.43) 24%, Φ M decrease in comparison with the controls was obtained. Different from several literature results, we showed that nano-TiO 2 particles at environmentally relevant concentrations affected microalgae physiology, and this was dependent on the endpoint used to evaluate the effect.