Toxicity and cytogenetic studies of ultrafine titanium dioxide in cultured rat liver epithelial cells.

The in vitro cytotoxicity and the induction of micronuclei of two ultrafine titanium dioxide (TiO(2)) samples was assessed in a rat liver epithelial cell (RLE) assay. Pigmentary TiO(2) was used as a control particle, and mitomycin C, a potent inducer of chromosome damage, was used as a positive control agent in the micronucleus experiments. Since photoexcitation of TiO(2) particles has been reported to increase the cell-killing effect of the dust, a duplicate series of experiments was carried out by irradiating the TiO(2) exposed cells with near-UV light. Neither of the ultrafine TiO(2) samples was toxic to the cells at the concentration range of 5-200 mug/cm(2). The UV treatment had no significant effect on the results. The induction of micronuclei was tested in three concentrations (5, 10 and 20 mug/cm(2)). None of the TiO(2) samples, either ultrafine or pigmentary, increased the numbers of micronuclei in the RLE cells. By contrast, all three samples had a slight decreasing effect on the frequency of micronuclei at the lowest treatment concentration of 5 mug/cm(2), both in the absence and in the presence of UV irradiation. The results suggest that ultrafine particles, similar to pigmentary TiO(2), have no direct clastogenic potential.