Elsevier

NanoImpact

Volume 19, July 2020, 100240
NanoImpact

Research paper
Advanced filtration and lung deposition models of airborne multi-walled carbon nanotubes for inhalation exposure assessment

https://doi.org/10.1016/j.impact.2020.100240Get rights and content

Highlights

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    Mixing states and agglomeration of CNTs affect the filtration efficiency.

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    Mixing states and agglomeration of CNTs influence the lung deposition.

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    Lung deposition of CNT agglomerates is higher than for single standing CNTs.

Abstract

Precise prediction of airborne carbon nanotube (CNT) filtration and deposition in the lung is of significant importance to find proper control media and to perform exposure assessment to quantify the toxicity for emitted airborne CNTs. We executed a systematic study in order to evaluate the inhalation exposure of inhaled single standing airborne multi-walled carbon nanotubes (MWCNTs) and CNT agglomerates, by assessing their filtration and deposition in the deep lung using calculation models. Filtration, inhalation and deposition were influenced by the agglomeration of the fibrous particles and by the agglomerate mixing state. 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. We verified our newly developed filtration model empirically. The calculated lung deposition for the realistic CNT mixtures and CNT agglomerates showed much higher deposition rates than that for single standing CNTs under a variety of flow conditions and in the size range from 76 to 500 nm. The lung deposition and the toxicity are both dependent on the CNT shape and form. Our study illustrates the necessity to consider the CNT morphology and agglomeration status in the evaluation of the airborne CNT health impact. The comparison between the developed lung deposition model and previous empirical study results showed that the particle deposition in the lung is mainly determined during inhalation.

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).ED=2.7Pe−23,EDR=1.24R2/3KuPe1/2,ER=1−αKuR21+R,EI=12Ku229.6−28a0.62R2−27.5R2.8Stk,Ef=ED+ER+EDR+EI,

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.

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