Studies On The Biological Safety Of Titanium Dioxide Nanoparticles

Nowadays, nano-sized TiO₂ is produced abundantly and used widely. More and more nanoparticles are entering into the environment. The risk of nano-TiO₂ should be reassessed because its special property such as small size, surface effect,more powerful photocatalytic ability.Several nano-TiO₂ powders with different size,different crystal form and different modification were studied. Their irritation to Chorioallantoic membrane(CAM)was tested, and their influnce to the blood vessel was observed. The acute toxicity of nano-TiO₂ to Caenorhabditis elegans was studied. The influence to the proliferation and melanin production of human malignant melanoma by nano-TiO₂ was investigated.The dissertation consists of three parts. In partâ… , HET-CAM (hen's egg test chorioallantotic membrane, HET-CAM) irritation test was carried out to evaluate the irritation of nano-TiO₂ to CAM. The development of the blood vessel on CAM was observed. In partâ…¡, Caenorhabditis elegans were exposed to nano-TiO₂ suspension with different concentrations for 24 hours. The toxicity was determined with the lethality rate. In partâ…¢,human malignant melanoma A375 was applied with different nano-TiO₂, with or without UVA radiation, the proliferation of cells was determined with the method of MTT assay, the melanin production was determined with the spallation of NaOH and the change of tyrosinase was measured with dioxyphenylalanine oxidation.The results are as followed:The HET-CAM results showed there's no irritant reaction for all the tested CAM, and the development of blood vessel was no obvious inflenced by the 5% nano-TiO₂ suspension.The 24 hour lethality rate showed that the anatase TiO₂ nanoparticles was more toxic generally than the retile TiO₂ nanoparticles. But there's no definite relation between the toxicity and particle size.At the UVA radiation condition, the toxicity to the human malignant melanoma A375 cells of both anatase and retile TiO₂ nanoparticles increased when the particle size decreased. Without light radiation, the 4nm and 10nm TiO₂ nanoparticles had similar cell tocixity while the SHU-403(anatase form, 50nm) nanoparticles showed more toxic than the others; the toxicity of all the three retile TiO₂ nanoparticles increased when the particle size decreased, showed size effect. At the similar particle size, anatase nanopartiles were much toxic than the retile ones and the toxicity of mixed crystal form P25 nanoparticles was between them. Surface modification could decline the photocatalytic ability of nano-TiO₂, thereby protecting the cells from burned by the ultraviolet. At the low concentration, nano-TiO₂ could decrease the melanin synthesis induced by UVA, showing resistant to tan.