Indium-Tin-Oxide (ITO) is a sintered mixture of indium- (In₂O₃) and tin-oxide (SnO₂) in a ratio of 90:10 (wt:wt) that is used for the manufacture of LCD screens and related high technology applications. Interstitial pulmonary diseases have recently been reported in workers from ITO producing plants. The present study was conducted to identify experimentally the exact chemical component responsible for this toxicity and to address possible mechanisms of action. The reactivity of respirable ITO particles was compared with that of its single components alone or their unsintered 90:10 mixture (MIX) both in vivo and in vitro. For all endpoints considered, ITO particles behaved as a specific toxic entity. In vivo, after a single pharyngeal administration (2–20 mg per rat), ITO particles induced a strong inflammatory reaction. At day 3, the inflammatory reaction (cell accumulation, LDH and protein in bronchoalveolar lavage fluid) appeared more marked with ITO particles than with each oxide separately or the MIX. This inflammatory reaction persisted and even worsened after 15 days. After 60 days, this inflammation was still present but no significant fibrotic response was observed. The cytotoxicity of ITO was assessed in vitro in lung epithelial cells (RLE) and macrophages (NR8383 cell line). While ITO particles (up to 200 μg/ml) did not affect epithelial cell integrity (LDH release), a strong cytotoxic response was found in macrophages exposed to ITO, but not to its components alone or mixed. ITO particles also induced an increased frequency of micronuclei in type II pneumocytes in vivo but not in RLE in vitro, suggesting the preponderance of a secondary genotoxic mechanism. To address the possible mechanism of ITO toxicity, reactive oxygen species production was assessed by electron paramagnetic resonance spectrometry in an acellular system. Carbon centered radicals (COO-·) and Fenton-like activity were detected in the presence of ITO particles, not with In₂O₃, SnO₂ alone, or the MIX. Because the unsintered mixture of SnO₂ and In₂O₃ particles was unable to reproduce the reactivity/toxicity of ITO particles, the sintering process through which SnO₂ molecules are introduced within the crystal structure of In₂O₃ appears critical to explain the unique toxicological properties of ITO. The inflammatory and genotoxic activities of ITO dust indicate that a strict control of exposure is needed in industrial settings.

Objective The use of nanotechnology is growing enormously and occupational physicians have an increasing interest in evaluating potential hazards and finding biomarkers of effect in workers exposed to nanoparticles. Methods A study was carried out with 36 workers exposed to (nano)TiO₂ pigment and 45 controls. Condensate (EBC) titanium and markers of oxidation of nucleic acids (including 8-hydroxy-2-deoxyguanosine (8-OHdG), 8-hydroxyguanosine (8-OHG), 5-hydroxymethyl uracil (5-OHMeU)) and proteins (such as o-tyrosine (o-Tyr), 3-chlorotyrosine (3-ClTyr) and 3-nitrotyrosine (3-NOTyr)) were analysed from samples of their exhaled breath. Results In the production workshops, the median total mass 2012 and 2013 TiO₂ concentrations were 0.65 and 0.40 mg/m³, respectively. The median numbers of concentrations measured by the scanning mobility particle sizer (SMPS) and aerodynamic particle sizer (APS) were 1.98×10⁴ and 2.32×10⁴ particles/cm³, respectively; and about 80% of those particles were smaller than 100 nm in diameter. In the research workspace, lower aerosol concentrations (0.16 mg/m³ and 1.32×10⁴ particles/cm³) were found. Titanium in the EBC was significantly higher in production workers (p<0.001) than in research workers and unexposed controls. Accordingly, most EBC oxidative stress markers, including in the preshift samples, were higher in production workers than in the two other groups. Multiple regression analysis confirmed an association between the production of TiO₂ and the levels of studied biomarkers. Conclusions The concentration of titanium in EBC may serve as a direct exposure marker in workers producing TiO₂ pigment; the markers of oxidative stress reflect the local biological effect of (nano)TiO₂ in the respiratory tract of the exposed workers.

Nanometric TiO₂ has been reported to be cytotoxic and genotoxic in different in vitro models when activated by UV light. However, a clear picture of the species mediating the observed toxic effects is still missing. Here, a nanometric TiO₂ powder has been modified at the surface to completely inhibit its photo-catalytic activity and to inhibit the generation of all reactive species except for singlet oxygen. The prepared powders have been tested for their ability to induce strand breaks in plasmid DNA and for their cytotoxicity and genotoxicity toward human keratinocyte (HaCaT) cells (100–500 μg mL⁻¹, 15 min UVA/B exposure at 216–36 mJ m⁻² respectively). The data reported herein indicate that the photo-toxicity of TiO₂ is mainly triggered by particle-derived singlet oxygen. The data presented herein contribute to the knowledge of structure–activity relationships which are needed for the design of safe nanomaterials.