(53c) Potential Inhalation Toxicity of Nanomaterials

Nanoparticles (manufactured) or ultrafine particles (naturally produced in the environment) are particles in at least one dimension < 0.1 microns (100 nanometers [nm]). Inhalation of potentially injurious particles small enough to travel to deep lung (fine particles - < 2.5 microns [2,500 nm] or ultrafine- (nano-) particles) can have different outcomes. For example, they can cause no biomedical consequences. Alternatively, they can cause and heal minor injuries in relatively healthy lung epithelial cells (LEC), lead to chronic degenerative lung disease or even to lung cancer if the LEC are injured, or become injured. Lung responses are influenced by repeated injury, or persistence of the nanoparticle. Particles < 0.5 microns (500 nm) are cleared from lung with minimal efficiency by lung phagocytes or simply ignored and travel to the pulmonary interstitial space. Lack of clearance can be one source of persistence of the particles and continued injury. Relative solubility is a second source of persistence for poorly soluble particles. In studies at Kansas State University, we have shown that non-toxic magnesium oxide (MgO), relatively insoluble in distilled water, is much more rapidly soluble in LEC tissue culture fluid (Hanks Balanced Salt Solution; distilled water peak ~2-4 days; HBSS peak < 1-3 hours). Peak dissolution increased > 10 fold with HBSS relative to distilled water. Speed and amount of solubility were related directly to the bicarbonate concentration (a major human body buffer) in the dissolving media. Contrast this to titanium dioxide or carbonaceous particles which are relatively insoluble and would be expected to persist. If sufficiently small particles would be expected to go to the interstitial space and remain as a potentially injurious source.

Research supported by US Marine Corps Systems Commend - M-2 Corporation, NanoScale Corporation and Kansas State University.