Freshwater algae show low-to-moderate susceptibility to TiO2 exposure, with more pronounced toxic effects in the presence of UV irradiation. It has also been shown that nano-sized TiO2 is significantly more toxic to algae Pseudokirchneriella sub-capitata than submicron-sized TiO2. Hund-Rinke and Simon reported that UV irradiated 25 nm TiO2 NPs are more toxic to green freshwater algae Desmodesmus subspicatus than UV irradiated 50 nm particles, which is in agreement with Hartmann et al. UV irradiated TiO2 NPs also inactivated other algae species such as Anabaena, Microcystis, Melsoira and Chroococcus. It was demonstrated that smaller particles have a greater potential to penetrate the cell interior than submicron-sized particles and larger aggregates. Studies have shown that the amount of TiO2 adsorbed on algal cells can be up to 2.3 times their own weight.
