Research paperAdvanced filtration and lung deposition models of airborne multi-walled carbon nanotubes for inhalation exposure assessment
Section snippets
Background
Filtration and inhalation models of aerosols, such as engineered nanoparticles, medicines, bacteria and viruses, have been discussed extensively in the last decades. Because both filtration and inhalation modelings are significant for preventing of inhalation exposure to toxic particles as asbestos fibers or viruses like SARS-CoV-2 (COVID-19), and curing a respiratory disease through an inhalation therapy (Basile, 2020; Ma-Hock et al., 2013; Fathizadeh, 2020; Donaldson and Tran, 2004,
Methods
In this study, we employed a fractal model for CNT agglomerates (Wang et al., 2015) and took into consideration the CNT agglomerate fraction in the airborne CNT mixture. The fractions were obtained by SEM (scanning electron microscope) image analysis of sampled aerosolized CNTs (Baytubes, Bayer Material Science, Germany) from a liquid suspension. We employed CNTs that had 15–20 nm diameters and 1–10 μm lengths. However, after the functionalization processes, which improved CNT dispersion in
Filtration model
The single fiber filtration model was employed in the study. Based on the twilled dutch wire mesh model (Sachinidou et al., 2017), different filtration mechanisms caused by diffusion (ED), interception (ER), interception of diffusing particles (EDR) and impaction (EI) were considered in the model. The detailed equations for spherical particles are shown in Eqs. (3), (4), (5), (6), (7), (8).
The total
Advanced filtration model
Filtration efficiencies by the wire mesh for spherical particles, single standing CNTs and CNT mixtures (including CNT agglomerates and single standing CNTs), which is a more realistic model for airborne CNTs, were calculated. The filtration efficiency of the wire mesh against CNT mixtures was experimentally obtained. Obtained filtration efficiencies in the size range of 50 nm to 500 nm were compared and shown in Fig. 5. Compared with the sphere model, CNT filtration efficiencies showed higher
Discussions
The purpose of this study was the evaluation of particle collection on filters and in the human lung not only for CNTs, but also for fibrous particles, which have strong tendency to bend, coil or agglomerate. Chen et al., 2012 found that CNTs tend to agglomerate in different shapes (mainly sphere like CNT agglomerates and some irregular shaped aggregates). Based on Chen et al., 2012 who recommended a separation of single standing CNT and isometric particles (sphere like particles) we applied
Conclusions
We revised previous models and developed the models for realistic CNT mixtures in air with a new approach using the mixing states of CNT agglomerates and single standing CNTs. The SEM results showed that the relative percentage of CNT agglomerates compared to single standing CNTs increased with increasing particle diameter.
The developed filtration model and the approach were verified empirically in the study. The calculated lung deposition for the realistic CNT mixtures showed much higher
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This study was partially supported by the Center for Filtration Research (CFR) at the University of Minnesota (MN, US). The authors thank Prof. Jing Wang for the fruitful discussion.
References (49)
- et al.
A multiple-path model of particle deposition in the rat lung
Fundam. Appl. Toxicol.
(1995) - et al.
Deposition of fibers in the rat lung
J. Aerosol Sci.
(1989) - et al.
Inertial and interceptional deposition of spherical particles and fibers in bifurcating airways
J. Aerosol Sci.
(1988) - et al.
An introduction to the short-term toxicology of respirable industrial fibres
Mutat. Res.
(2004) - et al.
Deposition of particles in the human respiratory tract in the size range 0.005–15 μm
J. Aerosol Sci.
(1986) - et al.
Comparison of black carbon concentration and particle mass concentration with elemental carbon concentration for multi-walled carbon nanotube emission assessment purpose
Carbon
(2017) - et al.
Natural and anthropogenic environmental nanoparticulates; their microstructural characterization and respiratory health implications
Atmos. Environ.
(2009) Theory of gravitational deposition of particles from laminar flows in channels
J. Aerosol Sci.
(1972)- et al.
Characteristics of airborne fractal-like agglomerates of carbon nanotubes
Carbon
(2015) - et al.
Models of human lung airways and their application to inhaled particle deposition
Bull. Math. Biol.
(1980)