Quantifying respiratory tract deposition of airborne graphene nanoplatelets: The impact of plate-like shape and folded structure

The booming development of commercial products containing graphene nanoplatelets (GNPs) triggers growing concerns over their release into the air. Precise prediction of human respiratory system deposition of airborne GNPs, especially in alveolar region, is very important for inhalation exposure assessment. In this study, the pulmonary deposition of airborne GNPs was predicted by the multiple-path particle dosimetry (MPPD) model with consideration of GNPs plate-like shape and folded structure effect. Different equivalent diameters of GNPs were derived and utilized to describe different deposition mechanisms in the MPPD model. Both of small GNPs (geometric lateral size dg < 0.1 m) and large GNPs (dg > 10 m) had high deposition fractions in human respiratory system. The total deposition fractions for 0.1 m and 30 m GNPs were 41.6% and 75.6%, respectively. Most of the small GNPs deposited in the alveolar region, while the large GNPs deposited in the head airways. The aerodynamic diameter of GNPs was much smaller than the geometric lateral dimension due to the nanoscale thickness. For GNPs with geometric lateral size of 30 m, the aerodynamic diameter was 2.98 m. The small aerodynamic diameter of plate-like GNPs enabled deposition in the alveolar region, and folded GNPs had higher alveolar deposition than planar GNPs. Heavy breathing led to higher GNPs deposition fraction in head airways and lower deposition fractions in the alveolar region than resting breathing. Our results reveal that large GNPs can have small enough aerodynamic diameters to be respirable and deposit beyond the ciliated airways. The plate-like morphology and folded structure of GNPs resulted in higher alveolar deposition compared to spherical particles.