Internal Exposure and Distribution of Airborne Fine Particles in the Human Body: Methodology, Current Understandings, and ResearchNeeds

Exposure to airbornefine particles (PM2.5, particulate matter with aerodynamicdiameter <2.5 mu m) severely threatens global human health. Understanding the distribution andprocesses of inhaled PM2.5in the human body is crucial to clarify the causal links betweenPM2.5pollution and diseases. In contrast to extensive research on the emission and formationof PM2.5in the ambient environment, reports about the occurrence and fate of PM2.5inhumans are still limited, although many studies have focused on the exposure and adverseeffects of PM2.5with animal models. It has been shown that PM2.5, especially ultrafine particles(UFPs), have the potential to go across different biological barriers and translocate intodifferent human organs (i.e., blood circulation, brain, heart, pleural cavity, and placenta). Inthis Perspective, we summarize the factors affecting the internal exposure of PM2.5and therelevant analytical methodology and review current knowledge about the exposure pathwaysand distribution of PM2.5in humans. We also discuss the research challenges and call for morestudies on the identification and characterization of key toxic species of PM2.5, quantification ofinternal exposure doses in the general population, and further clarification of translocation,metabolism, and clearance pathways of PM2.5in the human body. In this way, it is possible to develop toxicity-based air qualitystandards instead of the currently used mass-based standards.

Automated summary

Exposure to PM2.5 is a significant threat to human health globally. Understanding the distribution and processes of inhaled PM2.5 in the human body is crucial for establishing the causal links between PM2.5 pollution and diseases. However, research on the occurrence and fate of PM2.5 in humans is still limited. Therefore, further studies are needed to investigate the exposure pathways, distribution, and causal relationships between PM2.5 and diseases in the human body.