Airborne Aluminum as an Underestimated Source of Human Exposure: Quantification of Aluminum in 24 Human Tissue Types Reveals High Aluminum Concentrations in Lung and Hilar Lymph Node Tissues

Abstract

Aluminum (Al) is the most abundant metal in the earth's crust, and humans are exposed to Al through sources like food, cosmetics, and medication. So far, no comprehensive data on the Al distribution between and within human tissues were reported. We measured Al concentrations in 24 different tissue types of 8 autopsied patients using ICP-MS/MS (inductively coupled plasma-tandem mass spectrometry) under cleanroom conditions and found surprisingly high concentrations in both the upper and inferior lobes of the lung and hilar lymph nodes. Al/Si ratios in lung and hilar lymph node samples of 12 additional patients were similar to the ratios reported in urban fine dust. Histological analyses using lumogallion staining showed Al in lung erythrocytes and macrophages, indicating the uptake of airborne Al in the bloodstream. Furthermore, Al was continuously found in PM_2.5 and PM₁₀ fine dust particles over 7 years in Upper Austria, Austria. According to our findings, air pollution needs to be reconsidered as a major Al source for humans and the environment.

Keywords: ICP–MS; PM10–PM2.5; air pollution; aluminum; lumogallion; tissue distribution.

Figure 1

Statistically significant differences are shown for the following comparisons: hilar lymph node vs lung upper lobe; hilar lymph node vs lung inferior lobe; lung inferior lobe vs colon; lung inferior lobe vs vena cava. Data was log-transformed for better graphic representation. *p ≤ 0.05; **p ≤ 0.01; ****p ≤ 0.0001; ns not significant.

Figure 2

Lumogallion (left column, red Al-specific fluorescence) and H&E images (right column) of the hilar lymph node (A), upper lobe of the lung (B), inferior lobe of the lung (C), and duodenum (D) are shown for patient 4. Erythrocytes are stained red using H&E (indicated with triangles) and can be found inside blood vessels as well as within the tissue of upper and inferior lobes of the lung. The location of erythrocytes in H&E and that of Al signals in lumogallion staining overlap, showing that Al is bound in erythrocytes in lung tissues. Macrophages are prominent in C (larger dark-red areas outside blood vessels, indicated with arrows) and also contain Al. Brunner’s glands showed high Al signals and could be identified on H&E-stained slides (indicated with asterisks).