TRANSLOCATION OF ULTRAFINE INSOLUBLE IRIDIUM PARTICLES FROM LUNG EPITHELIUM TO EXTRAPULMONARY ORGANS IS SIZE DEPENDENT BUT VERY LOW

Abstract

Recently it was speculated that ultrafine particles may translocate from deposition sites in the lungs to systemic circulation. This could lead to accumulation and potentially adverse reactions in critical organs such as liver, heart, and even brain, consistent with the hypothesis that ultrafine insoluble particles may play a role in the onset of cardiovascular diseases, as growing evidence from epidemiological studies suggests. Ultrafine (192)Ir radio-labeled iridium particles (15 and 80 nm count median diameter) generated by spark discharging were inhaled by young adult, healthy, male WKY rats ventilated for 1 h via an endotracheal tube. After exposure, excreta were collected quantitatively. At time points ranging from 6 h to 7 d, rats were sacrificed, and a complete balance of (192)Ir activity retained in the body and cleared by excretion was determined gamma spectroscopically. Thoracic deposition fractions of inhaled 15- and 80-nm (192)Ir particles were 0.49 and 0.28, respectively. Both batches of ultrafine iridium particles proved to be insoluble (<1% in 7 d). During wk 1 after inhalation particles were predominantly cleared via airways into the gastrointestinal tract and feces. This cleared fraction includes particles deposited in the alveolar region. Additionally, minute particle translocation of <1% of the deposited particles into secondary organs such as liver, spleen, heart, and brain was measured after systemic uptake from the lungs. The translocated fraction of th…