Passage of Inhaled Particles Into the Blood Circulation in Humans

TLDR

Particulate air pollution is consistently linked to cardiovascular morbidity and mortality, yet the underlying mechanisms remain poorly understood. The study aimed to determine how rapidly and to what extent inhaled pollutant particles enter systemic circulation. Five healthy volunteers inhaled Technegas, an aerosol of ultrafine 99mTc‑labeled carbon particles (<100 nm), and the distribution of radioactivity was measured over time. Radioactivity appeared in blood within 1 minute, peaked between 10–20 minutes, persisted up to 60 minutes, and imaging revealed liver and other organ uptake, indicating that ultrafine carbon particles rapidly enter circulation and may underlie extrapulmonary effects of air pollution.

Abstract

Background — Pollution by particulates has been consistently associated with increased cardiovascular morbidity and mortality. However, the mechanisms responsible for these effects are not well-elucidated. Methods and Results — To assess to what extent and how rapidly inhaled pollutant particles pass into the systemic circulation, we measured, in 5 healthy volunteers, the distribution of radioactivity after the inhalation of “Technegas,” an aerosol consisting mainly of ultrafine 99m Technetium-labeled carbon particles (&lt;100 nm). Radioactivity was detected in blood already at 1 minute, reached a maximum between 10 and 20 minutes, and remained at this level up to 60 minutes. Thin layer chromatography of blood showed that in addition to a species corresponding to oxidized 99m Tc, ie, pertechnetate, there was also a species corresponding to particle-bound 99m Tc. Gamma camera images showed substantial radioactivity over the liver and other areas of the body. Conclusions — We conclude that inhaled 99m Tc-labeled ultrafine carbon particles pass rapidly into the systemic circulation, and this process could account for the well-established, but poorly understood, extrapulmonary effects of air pollution.