Nanomaterials

NTP inhalation studies on fullerene C60 were conducted through an NIEHS testing contract. Two 13-week inhalation studies of fullerene C60 were completed. Additional studies of fullerene C60 have examined potential impacts on the immune system. These studies of rodent lungs involved two distinct particle sizes of C60 atmospheres. Studies examined:

• Toxicity
• Tissue distribution
• Immunological effects
• Clearance in the lungs

Fullerene C60 was evaluated under a NIOSH-NIEHS Interagency agreement to provide a better assessment of US worker exposures and occupational health concerns.

The multiwalled carbon nanotubes (MWCNT) project examines the impact of nanotube length and diameter. Studies analyzed the toxicity of multiwalled carbon nanotubes in the lungs of animal models.

The initial phase of the project included the procurement and physical and chemical characterization of 24 commercially available carbon nanotubes to evaluate the diversity of commercially available materials. Results from this phase were used for selection of a specific test article for additional tests. Based on toxicity and clearance data, a 30-day study was designed to evaluate immunotoxicity at lower atmosphere concentrations. In addition, a chronic 2-year toxicity and carcinogenicity study in rats and mice exposed to these low concentrations of MWCNT is also ongoing.

Carbon nanotube exposure has been evaluated under a NIOSH-NIEHS Interagency agreement to provide a better assessment of US worker exposures and occupational health concerns.

National Institute for Occupational Safety and Health (NIOSH) staff, supported by a NIOSH-NIEHS Interagency agreement, conducted in vitro physicochemical analyses of a variety of micro and nanocrystalline cellulose (NCC) to assess dissolution and durability. Based on the persistence of nanocrystalline silver, NTP is developing plans for future in vivo studies of nanocrystalline cellulose.

As part of another interagency agreement with NIOSH, NTP is committed to an industry-wide exposure assessment as well as epidemiology studies of U.S. manufacturers of engineered carbonaceous nanomaterials (ECN). The information collected includes:

• Nanomaterials produced (including characterization of size and shape)
• Size of worker population by facility
• Tonnage of materials used or produced
• Workforce size
• Status

The U.S. Food and Drug Administration nominated nanoscale silver (n-Ag) for study by the NTP based on two factors:

• Increasing widespread use in drug, food, and cosmetic products
• The general lack of data on the toxicology and pharmacokinetics of these materials

The n-Ag project was conducted by scientists at the National Center for Toxicological Research (NCTR). In vitro toxicity and toxicokinetic studies on the effect of particle size of nanosilver pharmacokinetics were completed. Subchronic, or short-term, 13-week studies on different sizes of n-Ag have also been completed.

Staff at NCTR evaluated the kinetics of tissue distribution following intradermal injection of quantum dots.

Scientists also evaluated kinetics and tissue distribution after dermal exposure of quantum dots to intact and dermabraded mice. Results showed that absorption of nanoscale materials through the skin depends on skin barrier quality, and that lack of an epidermis provides access to quantum dot penetration.

NTP studies on nanoscale titanium dioxide have been conducted as part of the nanotechnology safety initiative. One study, together with other FDA-supported studies, examined the tissue distribution of titanium dioxide materials in animal models following skin exposure. Results indicated that intact skin is an effective barrier to titanium dioxide nanoscale materials.

Studies also examined the resulting protein expression in the lymph nodes of mice following titanium dioxide exposure.

Titanium dioxide was evaluated at NCTR supported by a NCTR-NIEHS Interagency agreement.