Effects of titanium nanoparticles on the photosynthesis, respiration, and physiological parameters in Dunaliella salina and Dunaliella tertiolecta

The development of nanotechnology and the upsurge of interest in titanium dioxide (TiO2) nanoparticles, especially the anatase and rutile crystalline phases, in consumer products such as paint and sunscreen, has polluted the aquatic environment and had adverse effects on living organisms, especially algae. Microalgae help to preserve the aquatic ecosystem. Accordingly, the present study investigated the effects of anatase and rutile TiO2 nanoparticles on the growth, photosynthetic pigment (chlorophyll), photosynthesis, and respiration rate of two algae species, Dunaliella salina (at NaCl concentrations of 1.5 and 0.5 M) and Dunaliella tertiolecta (at NaCl concentrations of 0.5 and 0.17 M). Treatment with 50, 100, 150, and 200 ppm of TiO2 and nano-TiO2 revealed that nano-TiO2 inhibited the growth and decreased the specific growth rate, chlorophyll, and photosynthesis of both algal species. The rate of decrease was significantly lower at higher concentrations of NaCl in both species; however, the greatest significant difference was observed at lower concentrations of NaCl in the anatase phase. The respiration rate increased for 2 weeks but, especially at lower concentrations of NaCl, the rate of increase declined at higher concentrations after exposure to both substances, especially in the anatase phase. The findings reveal that nano-TiO2 has a toxic effect on Dunaliella algae and its effect depends on the concentration of NaCl. The toxic effect was shown to decrease at higher concentrations of NaCl.