Functional Analysis of TiO2 Nanoparticle Toxicity in Three Plant Species

Titanium dioxide nanoparticles (nano-TiO 2 ) are manufactured and used worldwide in large quantities. However, phytotoxicity research on nano-TiO 2 has yielded confusing results, ranging from strong toxicity to positive effects. Therefore, in this research, the effects of nano-TiO 2 on the germination and root elongation of seed and seedlings were studied. Additionally, the uptake and physiological responses of mature plants were investigated. Physical chemistry data were analyzed to assess the availability of nano-TiO 2 . Finally, a hydroponic system designed to overcome nano-TiO 2 precipitation was used to reproduce the environmental conditions of actual fields. Nano-TiO 2 did not have any effect on seed germination or on most of the plant species tested. Nano-TiO 2 had positive effects on root elongation in some species. No physiological differences in enzyme activities or chlorophyll content were detected, even though the plants absorbed nano-TiO 2 . Physical chemistry data showed that nano-TiO 2 agglomerated rapidly and formed particles with much bigger hydrodynamic diameters, even in distilled water and especially in a hydroponic system. Furthermore, agglomerated nano-TiO 2 formed precipitates; this would be more severe in an actual field. Consequently, nano-TiO 2 would not be also readily available to plants and would not cause any significant effects on plants. Our results and other reports suggest that titanium itself is not phytotoxic, even though plants absorb titanium. In conclusion, nano-TiO 2 is not toxic to the three plant species, in vitro or in situ.