Analysis of carbon nanotube levels in organic matter: an inter-laboratory comparison to determine best practice

Abstract

Carbon nanotubes (CNTs) are increasingly being used in industrial applications, but their toxicological data in animals and humans are still sparse. To assess the toxicological dose-response of CNTs and to evaluate their pulmonary biopersistence, their quantification in tissues, especially lungs, is crucial. There are currently no reference methods or reference materials for low levels of CNTs in organic matter. Among existing analytical methods, few have been fully and properly validated. To remedy this, we undertook an inter-laboratory comparison on samples of freeze-dried pig lung, ground and doped with CNTs. Eight laboratories were enrolled to analyze 3 types of CNTs at 2 concentration levels each in this organic matrix. Associated with the different analysis techniques used (specific to each laboratory), sample preparation may or may not have involved prior digestion of the matrix, depending on the analysis technique and the material being analyzed. Overall, even challenging, laboratories’ ability to quantify CNT levels in organic matter is demonstrated. However, CNT quantification is often overestimated. Trueness analysis identified effective methods, but systematic errors persisted for some. Choosing the assigned value proved complex. Indirect analysis methods, despite added steps, outperform direct methods. The study emphasizes the need for reference materials, enhanced precision, and organized comparisons.

Keywords:

• Carbon nanotubes
• organic matter
• intercomparison
• biomonitoring

Acknowledgments

The authors thank the French National Institute for Research and Safety. Rachel Smith and Adam Laycock were supported by the NanoHarmony project under grant agreement No. 885931 of the European Union’s Horizon 2020 research and innovation program. We particularly acknowledge the efforts of Barbara Purson and William Vauquoy for round robin tests.

Disclosure statement

The authors declare that there are no conflicts of interest.

Data sharing

We agree to make data and materials supporting the results or analyses presented in their paper available upon reasonable request. It is up to the author to determine whether a request is reasonable.

Additional information

Funding

The authors thank the French National Institute for Research and Safety. Rachel Smith and Adam Laycock were supported by the NanoHarmony project under grant agreement No. 885931 of the European Union’s Horizon 2020 research and innovation program.