Negligible clearance of ultrafine particles retained in healthy and affected human lungs

¹ Dept of Public Health Sciences, Karolinska Institute; and Dept of Occupational and Environmental Health, Stockholm County Council
² Dept of Nuclear Medicine, Institution of Oncology-Pathology, Karolinska Hospital
³ Intelligent Aerosol Medicine, InAMed GmbH and
⁴ the Swedish Radiation Protection Authority
⁵ the Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden
⁶ GSF National Research Centre for Environment and Health, Institute for Inhalation Biology, Gauting and Munich, Germany

^* To whom correspondence should be addressed. E-mail: pernilla.wiebert{at}sll.se.

	Abstract

Ambient particles are believed to be a specific health hazard, although the underlying mechanisms are not fully understood. There are data in the literature indicating fast and substantial systemic uptake of particles from the lung. We have developed an improved method to produce ultrafine particles with more stable radiolabel and defined particles size range. Fifteen subjects inhaled ^99mTechnetium (^99mTc)-labeled carbonaceous particles, 100 nm in size. Radioactivity over the lung was followed for 70 h. We tested the clearance of these ultrafine particles from the lungs and specifically translocation to the circulation.

Lung retention for all subjects at 46 h was 99% (SD ±4.6). Cumulative leaching of ^99mTc activity from the particles was 2.6% (±0.96) at 70 h. Twenty-four h activity leaching in urine was 1.0% (±0.55).

We found no evidence of a quantitatively important translocation of 100 nm particles to the systemic circulation from the lungs. More research is needed to establish if the about 1% cleared activity originates from leached activity or insoluble translocated particles, and whether a few percent translocated particles is sufficient to cause harmful effects.

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