Pulmonary Retention of Ultrafine and Fine Particles in Rats

Abstract

In aerosol research, particle size has been mainly considered in the context of the role it plays in particle deposition along the respiratory tract. The possibility that the primary particle size may affect the fate of particles after they are deposited was explored in this study. Rats were exposed for 12 wk to aerosolized ultrafine (integral of 21 nm diameter) or fine (integral of 250 nm diameter) titanium dioxide (TiO2) particles. Other rats were exposed to TiO2 particles of various sizes (12, 21, 230, and 250 nm) by intratracheal instillation. After the rat lungs were extensively lavaged, analysis of particle content in the lavaged lungs, lavage fluid, and of lymphatic nodes was performed. Electron and light microscopy was also performed using unlavaged lungs. Both acute instillation and subchronic inhalation studies showed that ultrafine particles (integral of 20 nm) at equivalent masses access the pulmonary interstitium to a larger extent than fine particles (integral of 250 nm). An increasing dose in terms of particle numbers and a decreasing particle size promoted particle access into the interstitium. The translocation of particles into the interstitium appeared to be a function of the number of particles, and the process appeared to be related to the particle size, the delivered dose, and the delivered dose rate. A net effect of the preferential translocation of the smaller particles into the interstitium was a prolongation in their lung retention. After the 12-wk inhalation exposure, pulmonary clearance of ultrafine particles was slower (t1/2 = 501 days) than of larger particles (t1/2 = 174 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Ambient Particles and Health: Lines that Divide

“…The observed lags in the epidemiological studies between the increases in particle exposure and health outcomes might support the notion that particles incite an inflammatory reaction that appears to occur during the deposition and initial processing of inhaled particles, rather than later as the particles are further processed. 121 Inflammation may be related to the ability of particles to induce formation of free oxygen radicals, which in turn may depend on the particle concentration of surface-complexed iron (Fe 3+ ). [122][123][124] The toxicological studies are making a start at identifying specific particle components or features and elucidating mechanisms that may be responsible for the health effects attributed to particle exposure in the observational studies.…”

Mass size distributions and size resolved chemical composition of fine particulate matter at the Pittsburgh supersite

“…Ultrafine particles account for practically all the aerosol number concentration in the urban atmosphere, though their mass contribution is in general small. These particles can penetrate deep into the interstitial space of the lungs and overwhelm the alveolar macrophages, thereby impeding the natural cleaning mechanisms of the lungs (Oberdorster et al, 1994;Oberdorster, 1995Oberdorster, , 2001Ferin et al, 1992). Furthermore, inhalation of highly acidic particles can cause inflammation and irritation of the lung tissue; if the chemical constituents of the particles are carcinogenic, these particles may induce cancer tumors (Oberdorster and Yu, 1990;Donalson et al, 2002).…”

Air pollution and retained particles in the lung.

“…These particles, produced in combustion processes, are likely to contain condensates of toxic metals and surface acidity. In animal models, ultrafine particles appear to induce an intense inflammatory reaction and are believed to be translocated to the pulmonary interstitium in large numbers (7,8).…”