Exposure and Toxic effects of MWCNTs Released from Polymer Products

J. Sipe
Duke University,
United States

Keywords: nanoparticles, food, MNM


Manufactured nanomaterials (MNMs) are incorporated into consumer products to improve the quality of a product, revolutionizing the global market, from cosmetics to food storage containers to construction materials. Carbon nanotubes are one of the most commonly used nanomaterials. Multiwalled carbon nanotubes (MWCNTs) have diverse uses in products and have extraordinary mechanical properties of use to the polymer industry. Pristine MWCNT have resulted in toxicity in mice and fish; likewise, the release of MWCNTs during the nano-product’s lifecycle also concerning. MNMs can be released through mechanical stresses during use-phases during the product’s lifecycle such as sanding, chewing, and environmental degradation. However, few MNMs are released as pristine MNMs. They are usually attached to or surrounded by the product’s matrix, thus altering their release from the product, behavior in the environment, and toxicity. In this study, varying concentrations of MWCNT encased in a polymer polyethylene terephthalate glycol (PETG) mixture underwent mechanical stresses through a custom-built abrasion machine able to correlate use-phase events in the product’s life cycle. The release rate, fate, and behavior data were reported on two concentrations of MWCNTs (0.5 w. %, and 2 w. %) evenly dispersed in 3D printed PETG polymer during mechanical stress. The release rate ranged from 0.30 g/m2/min/J without MWCNT to 0.27 g/m2/min/J with 2 w. % of MWCNT supporting the hypothesis that product degradability is reduced during mechanical stress by the addition of MWCNTs. Most MWCNT were found to be embedded in the polymer but both embedded and protuberant MWCNTs impacted the size and shape of the microplastics produced and the hydrophobicity and surface charge of the polymer’s surface. The impact of MWCNT on produced particles behavior in three aquatic media (pure water, fresh water, and seawater) was also tested. Toxicity tests were performed using a transparent strain Japanese medaka (Oryzias latipes) with pristine MWCNT and MWCNT in the product matrix in various tissues and organ systems. In vivo observations revealed enlargement or leaking of the gallbladder, indicating possible changes in biliary function of the liver, and increased vascularization within the abdomen. This change was observed only in fish exposed to MWCNTs or the abraded nanotube composite material. This latter effect may be due to the smaller size of abraded particles from the composites compared with the non-composite or may be due to MWCNTs themselves. The comparison of pristine MWCNT toxicity versus released MWCNT toxicity allow to extract the effect of the product matrix. This factor can then be used as a proxy to predict the toxicity of released MWCNT toward other organisms using the MWCNT pristine dose response curve database. The resulting data were curated into the NanoInformatics Knowledge Commons (NIKC) and combined for analysis and display with a visualization tool called the Nano Product Hazard and Exposure Assessment Tool (NanoPHEAT). The NanoPHEAT application calculates an estimated exposure to materials of interest, including consideration of a “Matrix Release Factor” that accounts for changes in material availability and behavior as a function of the matrix in which it is included. The tool then superimposes the expected effective dose onto endpoint-specific dose-response curves for a variety of nanomaterials. Overall, the results suggest that for nano-products, the product’s matrix mostly controls the MWCNT release rate, fate, and behavior.