Safety evaluation of titanium dioxide nanoparticles by their absorption and elimination profiles

Our plain-English summary of Safety evaluation of titanium dioxide nanoparticles by their absorption and elimination profiles, by K. Sugibayashi, H. Todo, E. Kimura (The Journal of Toxicological Sciences, 2008).

The study

• Authors: K. Sugibayashi, H. Todo, E. Kimura
• Journal: The Journal of Toxicological Sciences
• Published: 2008;33(3):293-8
• Cited by: 37 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

If titanium dioxide nanoparticles are inert and non-biodegradable, they must be evaluated similarly to fullerenes, carbon nanotubes and asbestos. We surveyed the titanium level in typical raw food materials, and then intravenously injected titanium dioxide nanoparticles (primary particle diameter: 15 nm; secondary particle size: 220 nm) in mice and determined their tissue distribution and elimination. As a result, an unexpectedly high titanium concentration was observed in several foods. It was also detected in blood and tissues of healthy mice without administration of titanium dioxide nanoparticles. Then, forced i.v. injection of the nanoparticles was performed in mice. The titanim level was significantly increased in blood and tissues, but no increase was found in the brain after i.v. injection. Most titanium was concentrated in the liver after injection, but the liver level decreased over time (ca. 30% decrease in 1 month). These data show that titanium must be eliminated from the body, and suggest that we should reconsider an evaluation method for toxicity of titanium dioxide nanoparticles.

In plain English

This was a mouse experiment combined with a survey of titanium levels in foods. It did not study asbestos, which the authors mention only as a point of comparison. The authors measured titanium in a range of foods and found an unexpectedly high titanium concentration in several of them. Titanium was also found in the blood and tissues of mice that had not been given any nanoparticles. The authors measured 17.5 μg/ml of titanium in the mouse diet and reasoned that most titanium in the mice came from what they ate. They then injected a saline suspension of rutile titanium dioxide nanoparticles (primary particle size about 15 nm, secondary particle size about 220 nm) into the tail vein of mice. Titanium levels rose in blood and tissues but not in the brain. Most titanium went to the liver, where particles were seen in liver cells, and the liver level decreased over time. The authors concluded that their results, together with other studies, suggest titanium dioxide nanoparticles should be considered biodegradable or easily eliminated. They added that further experiments are necessary.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: animal experiment (intravenous injection in mice, with tissues sampled at 5 min, 72 hr and 1 month), plus a survey of titanium levels in foods
• Who was studied: laboratory mice (strain, weight and group sizes are unreadable in the text; the elimination figure reports 5 experiments per time point), and a range of food materials
• Exposure: titanium dioxide nanoparticles in rutile crystal form, with a mean primary particle diameter of 15 nm and a secondary particle size of about 220 nm, given as a 50 μl saline suspension injected into the tail vein (dose unreadable)
• Main results:
  • An unexpectedly high titanium concentration was found in several food materials
  • In mice not given nanoparticles, titanium in the blood and liver was printed as 4 and 15.4 μg/g tissue, respectively
  • The mouse diet contained 17.5 μg/ml titanium; the authors concluded that most titanium in mice came from ingested material
  • In injected mice, titanium levels increased in blood and tissues, but not in the brain
  • In injected mice, the titanium level in the liver decreased over time
  • Electron microscopy found the nanoparticles in liver cells of injected mice
• The authors' conclusion: The authors concluded that their results and those of other studies suggest titanium dioxide nanoparticles should be considered biodegradable or easily eliminated, and that the strategy for estimating their safety should be reconsidered
• Limitations the authors state:
  • The authors state that further experiments are necessary

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• Kinetics of the bronchoalveolar leucocyte response in rats during exposure to equal airborne mass concentrations of quartz, chrysotile asbestos, or titanium dioxide — K. Donaldson, R.E. Bolton, et al. (1988)
• Experimental studies in rats on the effects of asbestos inhalation coupled with the inhalation of titanium dioxide or quartz — J.M. Davis, A.D. Jones, et al. (1991)
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