July 2006 Symposium on Nanotechnology and the Environment: Session 2: Potential Exposure Scenarios and Potential Toxicity of Nanomaterials
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July 12, 1:00-2:00 PM
Dr. David B. Warheit, E.I. Dupont de Nemours and Co., Inc. Haskell Laboratory for Toxicity and Industrial Medicine
AbstractImpact of Nanoparticulates on Respiratory Health Effects: Toxicity is not always dependent solely upon Particle Size and Surface Area.
"Environmental Impact of Nanotechnology: Big Things Come in Little Packages"
The results of several lung toxicology studies in rats have demonstrated that ultrafine or nanoparticles (generally defined as particles in the size range < 100 nm) administered to the lungs produce enhanced inflammatory responses when compared to fine-sized particles of similar chemical composition at equivalent doses. However, the common perception that nanoparticles are always more toxic than finesized particles is based upon a systematic comparison of only 2 particle-types, namely, titanium dioxide and carbon black particles. Apart from particle size and corresponding surface area considerations, several additional factors may play more important roles in influencing the pulmonary toxicity of nanoparticles. These include, but are not limited to:
- surface treatments/coatings of particles;
- the aggregation/disaggregation potential of aerosolized particles;
- the method of nanoparticle synthesis - i.e., whether the particle was generated in the gas or liquid phase (i.e., fumed vs. colloidal/precipitated);
- translocation potential of the particle;
- particle shape; and
- surface charge.
Results of pulmonary bioassay hazard/safety studies will be presented demonstrating that fine-sized quartz particles (1.6 Ám) may produce greater pulmonary toxicity (inflammation, cytotoxicity, cell proliferation and/or histopathology) in rats when compared to nanoscale quartz particles (50 nm), but not when compared to smaller nanoquartz sizes (e.g., < 30 nm). In addition, other studies have demonstrated no measurable difference in pulmonary toxicity indices among particle-types when comparing exposures in rats to 1) fine-sized TiO2 particles (300 nm - 6 m^2/g (surface area); 2) TiO2 nanodots (6-10 nm - 169 m^2/g); or 3) TiO2 nanorods (25 m^2/g). Finally, studies will be presented which demonstrate that varying surface treatments on finesized TiO2 particles influence lung responses.
In summary, some important take-home messages are the following:
- Risk is a product of Hazard and Exposure;
- In general, one cannot assume that nanomaterials have the same chemistry or biology (i.e., toxicity) as their bulk counterparts; therefore, the hazards of each particle-type should be tested on a case-by-case basis.