Pulmonary toxicity studies in rats demonstrate that lung exposures to ultrafine or nanoparticles produce greater adverse inflammatory responses compared with larger particles of identical composition at equivalent mass concentrations. Surface properties (particularly surface area) and free radical generation by the interaction of particles with cells appear to play important roles in nanoparticle toxicity. Contributing to these effects is the very high size-specific deposition of nanoparticles when inhaled as singlet rather than aggregated particles. Some evidence suggests that inhaled ultrafine or nanoparticles, following deposition in the lung, largely escape alveolar macrophage surveillance and gain access to the pulmonary interstitium, a potentially vulnerable anatomical compartment. Results from the limited toxicological database have fostered the perception that all nanoparticles are toxic.
