Biological effects of TiO₂ and CeO₂ nanoparticles on the growth, photosynthetic activity, and cellular components of a marine diatom Phaeodactylum tricornutum

It is very important to have a good understanding of the biological effects of nanoparticles (NPs) on marine diatoms. In this study, the physiological and biochemical responses of a marine diatom Phaeodactylum tricornutum to titanium dioxide NPs (nano-TiO₂) and cerium oxide NPs (nano-CeO₂) were compared and evaluated using 96 h growth tests in a batch-culture system. At 96 h of exposure, the growth inhibition rate (IR, %) of P. tricornutum increased from 5.46 to 27.31% with increasing nano-TiO₂ concentrations from 2.5 to 40 mg L⁻¹. The maximum IR of 49.59% occurred in 40 mg L⁻¹ nano-TiO₂ treatments at 48 h of exposure. Growth of the diatom was increased in low nano-CeO₂ treatments (≤ 5 mg L⁻¹), but was inhibited in high nano-CeO₂ treatments (≥ 10 mg L⁻¹). Large aggregates of NPs were attached to the cells of P. tricornutum in 20 and 40 mg L⁻¹ nano-TiO₂ and nano-CeO₂ treatments. In addition, the effective quantum yields (Φ_PSII) of P. tricornutum in 40 mg L⁻¹ nano-TiO₂ and nano-CeO₂ treatments were 83.33 and 71.13% of that in the controls at 96 h of exposure, respectively. Compared with that of the controls at 96 h of exposure, chlorophyll a content, soluble sugar content, malondialdehyde (MDA) content, SOD and POD activities of P. tricornutum in 40 mg L⁻¹ nano-TiO₂ and nano-CeO₂ treatments increased by 57.56, 142.97, 373.25, 698.76, 204.85% and 21.43, 89.41, 194.97, 340.05, 502.86%, while soluble protein content decreased by 70.38 and 28.64%, respectively. These findings will be helpful to understand the effect mechanisms of NPs on marine organisms. - Highlights: • Photosynthetic activity of P. tricornutum was inhibited by nano-TiO₂ and nano-CeO₂. • Soluble sugar may serve as an osmotic agent to improve resistance of the diatom. • Physiological effects of both NPs on the diatom were caused by ROS generation. • SOD and POD were considered as a stimulatory response of the diatom to both NPs.