Slow lung clearance and limited translocation of four sizes of inhaled iridium nanoparticles

Abstract

BackgroundConcerns 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.MethodsRats 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.ResultsLong-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.ConclusionsSlow 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-017-0185-5) contains supplementary material, which is available to authorized users.

Advances in element speciation analysis of biomedical samples using synchrotron-based techniques

“…Finally, despite the lack of consistent sample amount, preliminary data on iridium NPs speciation were reported by Buckley and collaborators [69]. In this work, elemental maps of lung rats exposed to different Ir NPs sizes were produced by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and XRF.…”

Functional neurotoxicity and tissue metal levels in rats exposed subacutely to titanium dioxide nanoparticles via the airways

“…With iridium NPs inhaled by rats, ca. 5 times less translocation of 75 nm size NPs than of 10 nm ones from the lungs to liver and kidneys was reported 28 , underlining the effect of NP size on crossing barriers. Likewise, breakdown of bloodbrain barrier and neuronal damage caused by metal NPs, given ip., was more severe with 20-30 nm than with 56-60 nm or >100 nm particles 29 .…”

Organ burden of inhaled nanoceria in a 2-year low-dose exposure study: dump or depot?

“…The ratios of liver to lung burdens are low with a peak at the 12-month time point followed by a leveling off or reduction for all investigated exposure concentrations. Furthermore, a linear relationship between the retained dose in the lung ([mg/organ]) and the organ burden of the liver ([mg/organ]) was detected (Figure 8, R 2 ¼ 0.88; Buckley et al 2017).…”