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There is evidence indicating that humans may develop influenza-like symptoms after inhalation of fumes resulting from pyrolysis of polymers (e.g., Teflon), and from freshly produced fumes containing various oxides of metals. Exceptionally even more severe health effects have been reported. It seems that an essential factor in the generation of fume-fever is the ultrafine size of the inhaled particles. To test the hypothesis that ultrafine particles differ in their effect on the lung from larger particles, we compared effects on rats exposed to two types of anatase-titanium dioxide (TiO2) particles: TiO2-D with primary particle diameter of 20 nm, or TiO2-F with primary particle diameter of 250 nm. TiO2 is generally considered a substance with very low chemical toxicity. The rats were exposed by single intrapulmonary instillation, or by repeated inhalation exposures (12 weeks).

Accidental exposure to fumes arising from thermal degradation events is a major concern for manned space missions. Both particulate and gas phase components may be responsible for severe pulmonary damage occurring from such exposure. Results from our recent studies implicate ultrafine particles (particle diameter in the nm range) as potentially severe pulmonary toxicants. We have conducted a number of in vivo (inhalation and intratracheal instillation studies in rats) and in vitro studies to test the hypothesis that ultrafine particles elicit significantly greater adverse pulmonary effects than larger-sized particles. We used as surrogate particles ultrafine TiO2 particles (12 and 20 nm diameter) and carbon black (20 nm diameter).