title: Slow lung clearance and limited translocation of four sizes of inhaled iridium nanoparticles.
abstract: Concerns have been expressed that inhaled nanoparticles may behave differently to larger particles in terms of lung clearance and translocation, with potential implications for their toxicity. Studies undertaken to investigate this have typically involved limited post-exposure periods. There is a shortage of information on longer-term clearance and translocation patterns and their dependence on particle size, which this study aimed to address.
  
  
  
  Rats were exposed (<3 h) nose-only to aerosols of spark-generated radioactive iridium-192 nanoparticles of four sizes: 10 nm, 15 nm, 35 nm and 75 nm (count median diameter) (aerosol mass concentrations 17, 140, 430, and 690 μg/m3, respectively). The content of iridium-192 in the whole animal, organs, tissues, and excreta was measured at various times post-exposure to ≥ 1 month. Limited toxicological investigations were undertaken for the 10 nm aerosol using bronchoalveolar lavage fluid. Elemental maps of tissue samples were produced using laser ablation inductively coupled plasma mass spectrometry and synchrotron micro-focus x-ray fluorescence. The chemical speciation of the iridium was explored using synchrotron micro focus x-ray near-edge absorption spectroscopy.
  
  
  
  Long-term lung retention half-times of several hundred days were found, which were not dependent on particle size. There was significant variation between individual animals. Analysis of bronchoalveolar lavage fluid for the 10 nm aerosol indicated a limited inflammatory response resolving within the first 7 days. Low levels of, particle size dependent, translocation to the kidney and liver were found (maximum 0.4% of the lung content). Any translocation to the brain was below the limits of detection (i.e. < 0.01% of the lung content). The kidney content increased to approximately 30 days and then remained broadly constant or decreased, whereas the content in the liver increased throughout the study. Laser ablation inductively coupled plasma mass spectrometry analysis indicated homogeneous iridium distribution in the liver and within the cortex in the kidney.
  
  
  
  Slow lung clearance and a pattern of temporally increasing concentrations in key secondary target organs has been demonstrated for inhaled iridium aerosol particles < 100 nm, which may have implications for long-term toxicity, especially in the context of chronic exposures.
authors.affiliation: Public Health England, Centre for Radiation, Chemical and Environmental Hazards, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0RQ, UK.
authors.forename: Alison
authors.initials: A
authors.lastname: Buckley
authors.affiliation: Public Health England, Centre for Radiation, Chemical and Environmental Hazards, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0RQ, UK.
authors.forename: James
authors.initials: J
authors.lastname: Warren
authors.affiliation: Public Health England, Centre for Radiation, Chemical and Environmental Hazards, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0RQ, UK.
authors.forename: Alan
authors.initials: A
authors.lastname: Hodgson
authors.affiliation: Public Health England, Centre for Radiation, Chemical and Environmental Hazards, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0RQ, UK.
authors.forename: Tim
authors.initials: T
authors.lastname: Marczylo
authors.affiliation: Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Ignatyev
authors.affiliation: Public Health England, Centre for Radiation, Chemical and Environmental Hazards, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0RQ, UK.
authors.forename: Chang
authors.initials: C
authors.lastname: Guo
authors.affiliation: Public Health England, Centre for Radiation, Chemical and Environmental Hazards, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0RQ, UK. rachel.smith@phe.gov.uk.
authors.forename: Rachel
authors.identifier: 0000-0002-9784-3586
authors.initials: R
authors.lastname: Smith
mesh_terms: D000336:Aerosols; D000818:Animals; D001692:Biological Transport; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D002470:Cell Survival / Q000187:drug effects; D005260:Female; D019570:Inhalation Exposure; D007495:Iridium / Q000737:chemistry / Q000493:pharmacokinetics* / Q000633:toxicity; D008168:Lung / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000633:toxicity; D009928:Organ Specificity; D010316:Particle Size; D011921:Rats, Inbred WKY; D014018:Tissue Distribution
chemical_list: D000336:Aerosols; D007495:Iridium
keywords: In vivo study; Inhalation exposure; Lung clearance; Nanoparticles; Rat; Tissue distribution; Toxicity