A morphologic study on the fate of ultrafine silver particles: Distribution pattern of phagocytized metallic silver in vitro and in vivo

The distribution pattern of inhaled particles is an important factor for th e evaluation of health effects. In this study, rye morphologically investig ated the fate of agglomerated ultrafine particles in macrophages in vitro a nd in vivo. Metallic silver (Ag) was chosen as a test particle, since it ca n be easily produced and detected by elemental and morphologic analyses. Ul trafine Ag particles generated by an electric spark generator in an argon a tmosphere were collected on PTFE filters. The particles were suspended in d istilled water and adjusted to different concentrations (10 mu g/ml to 1 mg /ml) with phosphate-buffered saline (PBS). For the in vitro study, J774 mac rophage cell suspensions (200,000 cells in 400 mu l medium) were plated in small chambers. Six hours later, 100 mu l of the silver-PBS suspension was added to each chamber. For the next 9 days, the chamber slides were examine d daily with an inverted microscope in order to detect agglomerated particl es in the cell. The medium was changed every day, and Ag in the medium was checked by inductively coupled plasma mass spectrometry (ICP-MS). On days 1 , 3, 5, 7, and 9, cells in the chambers were fixed with 2.5% buffered gluta raldehyde and examined ultrastructurally. For the in vivo study using F344 rats, 50 mu g Ag particles were instilled intratracheally. On days 1, 4, an d 7 following instillation, rats were sacrificed and the lungs were examine d morphologically. The Ag content in the lung liver and lung-associated lym ph nodes was analysed by ICP-MS. in the in vitro study, the dose-dependent presence of agglomerated particles was observed in J774 cells. The size and form of particles remained unchanged throughout the observation period. El ectron microscopy with x-ray microanalysis showed that both single and aggl omerated Ag particles were observed in the dilated phagolysosome of J774 ce lls. In the in vivo study, focal accumulation of Ag-particle-laden alveolar macrophages was found Ag particles were also observed in the alveolar wall . Ag content in the lung was constant between day 1 and day 7 indicating th at no rapid particle translocation from the lung to other organs had taken place in this time period. In vitro and in vivo studies suggested that aggl omerated Ag particles remained in targets for a given period of time-at lea st up to 7 days.