Distribution of titanium dioxide in mice after nasal inhalation using SRXRF and ICP-MS

TiO2, a noncombustible and odorless white powder, naturally exists in antase, rutile and brookite. It is frequently used as a white pigment for a wide range of paints, paper, plastics, ceramics, and the like. TiO2 of size is used for cleaning air, antibacterial and decomposing organic in wastewater because of its photocatalytic property. TiO2 inhalation is the most common route of exposure in industry. After inhalation by human or rodents, TiO2 can induce inflammation and pulmonary lesions, which even cause lung cancer by long-term exposure to TiO2 powder. In this paper, the distributions of titanium dioxide in different organs and tissues of mice, in particular in brain, were investigated after inhalation of TiO2 suspension. Twenty ICR mice (body weight 21±2 g) were randomly divided into four groups: A (80 nm TiO2), B (25 nm TiO2), C (Control for H2O) and D (Micrometer TiO2). Each rat was given 25 μl TiO2 suspension for the first five days at a time, and there was no significant difference of growth rate in body weight. Subsequently, only 10 μl TiO2 suspension was inhaled each time every other day. After one month, all the animals were sacrificed and blood samples were collected through extirpating eyeball. The tissues and organs, such as heart, liver, spleen, kidney, lung and brain, were excised and weighed. All samples were stored at -20 degree C until used. The brains were removed and frozen sections (50 μm) were cut in coronal plane on a freezing microtome. The change of neurons in brain was observed under a light microscope after Nissl staining. The positional distributions of titanium in the olfactory bulb, cerebral cortex, hippocampus and thalamus areas were measured by Synchronization Radiation X-ray fluorescence (SRXRF) at Beijing Synchrotron Radiation Facility. An Al absorber: foil was used to reduce the lower energy intensity of the white light. The spectra were analyzed by AXIL program. The preliminary result showed that the distribution area of micro TiO2 was wider than nano TiO2 in olfactory bulb and brain, and micro TiO2 was easier to entry into olfactory bulb through olfactory tract than nano TiO2. Possibly this is because nano TiO2 is prone to aggregate and suspend in H2O solution. Quantitative titanium contents in visceral organs were determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS, Thermo Elemental X7, Thermo Electron Co.). The selected tissues (200-300 mg) were digested by nitric acid (MOS grade) at about 140 degree C. H2O2 (MOS grade) was used to driven off the nitric vapor until the solution was clear. Finally, the solution volume was fixed to 3 ml by 2 % nitric acid. The single indium solution (20 ppb) was chosen as the internal standard element. The detection limit of Ti was several ng/ml. The present results indicate that TiO2 could be translocated to the brain through the olfactory pathway and induce irregular arrangement of neurons and glial cells in the hippocampal region and cerebral cortex. Metabolic way of TiO2 in brain and its potential neurotoxicity should be investigated further.