National Toxicology Program

Ongoing research activities are initially focusing on 4 classes of materials:

1. Metal Oxides
2. Fluorescent Crystalline Semiconductors (Quantum dots)
3. Fullerenes
4. Nanotubes

Metal oxides

Initial focus is on nanoscale titanium dioxide and zinc oxide due to their presence in cosmetics. Ongoing and/or planned activities:

• Characterization of size, crystallinity, and coating of these metal oxides in representative commercial sunscreens
• Evaluation of photoactivation of titanium dioxide in in vitro, ex vivo, and in vivo models
• Dermal penetration of titanium dioxide in in vivo and in vitro models
• Phototoxicology  of titanium dioxide in mice
• Photocarcinogenicity of titanium dioxide in transgenic mice

Fluorescent Crystalline Semiconductors (Quantum Dots)

Initial focus is on cadmium selenide/zinc sulfide spheres and rods of varying sizes and surface chemistry as a model system to test hypotheses about role of size and surface chemistry on tissue distribution.  Ongoing and/or planned activities:

• Synthesis and characterization of specific materials
• Development of quantitative fluorescent microscopy system and IPC-mass spectroscopy  approach for evaluating tissue levels
• Quantitative evaluation of the tissue distribution following dermal and systemic routes of exposure

Fullerenes

Initial focus is on carbon based fullerenes of varying cage size and surface derivatisation.  Ongoing and/or planned activities:

• Physicochemical characterization of procured materials and formulation development
• In vivo repeat dose toxicity studies following oral exposure
• Pulmonary toxicity and evaluations following a single intratracheal instillation
• Immunotoxicological evaluation of fullerene C60

Nanotubes

Initial focus is on single walled carbon nanotubes.  Through a NIEHS-NIOSH interagency agreement NTP is supporting the development of exposure systems for inhalation toxicity studies of single walled nanotubes.