Effective density of inhaled environmental and engineered nanoparticles and its impact on the lung deposition and dosimetry

Abstract

Background Airborne environmental and engineered nanoparticles (NPs) are inhaled and deposited in the respiratory system. The inhaled dose of such NPs and their deposition location in the lung determines their impact on health. When calculating NP deposition using particle inhalation models, a common approach is to use the bulk material density, ρb, rather than the effective density, ρeff. This neglects though the porous agglomerate structure of NPs and may result in a significant error of their lung-deposited dose and location. Results Here, the deposition of various environmental NPs (aircraft and diesel black carbon, wood smoke) and engineered NPs (silica, zirconia) in the respiratory system of humans and mice is calculated using the Multiple-Path Particle Dosimetry model accounting for their realistic structure and effective density. This is done by measuring the NP ρeff which was found to be up to one order of magnitude smaller than ρb. Accounting for the realistic ρeff of NPs reduces their deposited mass in the pulmonary region of the respiratory system up to a factor of two in both human and mouse models. Neglecting the ρeff of NPs does not alter significantly the distribution of the deposited mass fractions in the human or mouse respiratory tract that are obtained by normalizing the mass deposited at the head, tracheobronchial and pulmonary regions by the total deposited mass. Finally, the total deposited mass fraction derived this way is in excellent agreement with those measured in human studies for diesel black carbon. Conclusions The doses of inhaled NPs are overestimated by inhalation particle deposition models when the ρb is used instead of the real-world effective density which can vary significantly due to the porous agglomerate structure of NPs. So the use of realistic ρeff, which can be measured as described here, is essential to determine the lung deposition and dosimetry of inhaled NPs and their impact on public health. Graphical abstract

Comparison of size distribution and electrical particle sensor measurement methods for particle lung deposited surface area (LDSAal) in ambient measurements with varying conditions

“…The particle lung deposition is driven by the diffusion with smaller particles (roughly < 0.1 µm) which is dependent on the mobility equivalent size whereas larger particles (> 0.5 µm) deposit due to impaction and sedimentation which are depended on the aerodynamic size (Hofmann et al 2011). Therefore, the particle effective density not only affects the comparability of the devices, but it also affects the particle lung deposition efficiencies (Löndahl et al 2014, Lizonova et al 2024) and, hence, the accuracy of the size distribution methods in terms of LDSA al . Also, it is worth noting that the size ranges of the size distribution measurements vary depending on the study and the device (also in this study), and the studied size range is not typically considered when reporting LDSA al concentration, even though it can considerably affect the results.…”

“…Moreover, the hygroscopic growth of particles in the lungs is often neglected in LDSA al measurements as it requires detailed information of the particle composition. Both the effective density and the hygroscopic growth can considerably change the particle lung deposition efficiencies (e.g., Löndahl et al 2014, Vu et al 2015, Lizonova et al 2024). These factors are however practically challenging to consider in air quality monitoring measurements as they require additional instrumentation which cannot be considered as a realistic approach with dense air quality monitoring networks.…”

Cytotoxicity and genotoxicity induced by metal-based nanoparticles in humans and animals

“…The majority of these particles are found in the epithelium of terminal airway structures and gas exchange zones. Nonetheless, the lungs feature a robust immune system consisting of upper and lower airways, as well as alveolar sacs that remove deposited nanoparticles (Lizonova et al 2024). Constant inhalation leads to the accumulation of insoluble and non-degradable particles with a longer lifespan in the lungs (Abdelaziz et al 2018) migrate from the alveoli to the larynx, where they are ingested, digested, and ejected from the body (Tammam et al 2015).…”