Physicochemical characterization and genotoxicity of the broad class of carbon nanotubes and nanofibers used or produced in U.S. facilities

Abstract

Background Carbon nanotubes and nanofibers (CNT/F) have known toxicity but simultaneous comparative studies of the broad material class, especially those with a larger diameter, with computational analyses linking toxicity to their fundamental material characteristics was lacking. It was unclear if all CNT/F confer similar toxicity, in particular, genotoxicity. Nine CNT/F (MW #1–7 and CNF #1–2), commonly found in exposure assessment studies of U.S. facilities, were evaluated with reported diameters ranging from 6 to 150 nm. All materials were extensively characterized to include distributions of physical dimensions and prevalence of bundled agglomerates. Human bronchial epithelial cells were exposed to the nine CNT/F (0–24 μg/ml) to determine cell viability, inflammation, cellular oxidative stress, micronuclei formation, and DNA double-strand breakage. Computational modeling was used to understand various permutations of physicochemical characteristics and toxicity outcomes. Results Analyses of the CNT/F physicochemical characteristics illustrate that using detailed distributions of physical dimensions provided a more consistent grouping of CNT/F compared to using particle dimension means alone. In fact, analysis of binning of nominal tube physical dimensions alone produced a similar grouping as all characterization parameters together. All materials induced epithelial cell toxicity and micronuclei formation within the dose range tested. Cellular oxidative stress, DNA double strand breaks, and micronuclei formation consistently clustered together and with larger physical CNT/F dimensions and agglomerate characteristics but were distinct from inflammatory protein changes. Larger nominal tube diameters, greater lengths, and bundled agglomerate characteristics were associated with greater severity of effect. The portion of tubes with greater nominal length and larger diameters within a sample was not the majority in number, meaning a smaller percentage of tubes with these characteristics was sufficient to increase toxicity. Many of the traditional physicochemical characteristics including surface area, density, impurities, and dustiness did not cluster with the toxicity outcomes. Conclusion Distributions of physical dimensions provided more consistent grouping of CNT/F with respect to toxicity outcomes compared to means only. All CNT/F induced some level of genotoxicity in human epithelial cells. The severity of toxicity was dependent on the sample containing a proportion of tubes with greater nominal lengths and diameters.

In vitro-in vivo correlations of pulmonary inflammogenicity and genotoxicity of MWCNT

“…Similarly, high levels of DNA strand breaks were observed in mouse lung tissue for all doses [22]. Accordingly, length of MWCNT has been suggested as predictor of genotoxicity [62]. The unaltered levels of DNA strand breaks in A549 cells exposed to long MWCNT might indicate the limitation of testing some NM, such as stiff and long MWCNT, in 2D cell cultures; the A549 might be too static to obtain the effects observed in vivo, where damage could be generated by the stiff fibers in a moving lung.…”

“…DNA damage caused by MWCNT has been linked to ROS production and oxidative stress [61]. We have previously shown large ROS production by DCFH oxidation assay with short MWCNT, including NRCWE-026 (same product but a different batch of NM-400; contains more Al 2 O 3 ) [14], NM-403, as well as NRCWE-040, − 041, and − 042 [14,62]]. This might explain the higher levels of DNA strand breaks in cells exposed to short MWCNT.…”

Oxidant-induced epithelial alarmin pathway mediates lung inflammation and functional decline following ultrafine carbon and ozone inhalation co-exposure

“…Ferric Reducing Ability of Serum (FRAS) Assay: FRAS assay was performed to study acellular oxidant generation ability of individual and co-exposures by following the already published methodology [ 31 , 32 ] with a slight modification. In order to accurately mimic the inhalation exposure and eliminate the artifacts that might arise due to interaction with room air, we bubbled aerosols (air, CB, O 3 and CB + O 3 ) for 5 min through the human serum and proceeded to quantify the changes by exactly following the previously published standardized methodology.…”

Profiling of Sub-Lethal in Vitro Effects of Multi-Walled Carbon Nanotubes Reveals Changes in Chemokines and Chemokine Receptors

“…CNTs have received particular attention due to their apparent similarities with other fiber-like materials, although inadequate or limited evidence of carcinogenicity exists for most CNTs [ 10 ]. Notwithstanding, in a recent study of seven different CNTs and two carbon nanofibers (CNFs), all the tested materials except one highly aggregated MWCNT sample induced genotoxicity in human bronchial epithelial cells (BEAS-2B) [ 11 ]. There was a tendency for CNTs/CNFs with increasing length and diameter to display slightly greater toxicity.…”