Evaluating the evidence on genotoxicity and reproductive toxicity of carbon black: a critical review

Abstract

Carbon black is produced industrially by the partial combustion or thermal decomposition of gaseous or liquid hydrocarbons under controlled conditions. It is considered a poorly soluble, low toxicity (PSLT) particle. Recently, results from a number of published studies have suggested that carbon black may be directly genotoxic, and that it may also cause reproductive toxicity. Here, we review the evidence from these studies to determine whether carbon black is likely to act as a primary genotoxicant or reproductive toxicant in humans. For the genotoxicity endpoint, the available evidence clearly shows that carbon black does not directly interact with DNA. However, the study results are consistent with the mechanism that, at high enough concentrations, carbon black causes inflammation and oxidative stress in the lung leading to mutations, which is a secondary genotoxic mechanism. For the reproductive toxicity endpoint for carbon black, to date, there are various lung instillation studies and one short-term inhalation study that evaluated a selected number of reproduction endpoints (e.g. gestational and litter parameters) as well as other general endpoints (e.g. gene expression, neurofunction, DNA damage); usually at one time point or using a single dose. It is possible that some of the adverse effects observed in these studies may be the result of non-specific inflammatory effects caused by high exposure doses. An oral gavage study reported no adverse reproductive or developmental effects at the highest dose tested. The overall weight of evidence indicates that carbon black should not be considered a direct genotoxicant or reproductive toxicant.

Keywords:

• Carbon black
• genotoxicity
• mutagenicity
• mode of action
• reactive oxygen species
• reproductive toxicity
• developmental toxicity

Acknowledgements

We thank the members of the Scientific Advisory Group to the International Carbon Black Association (ICBA) for reviewing and helping to improve the manuscript. We particularly would like to thank the four anonymous peer reviewers selected by the Editor for their excellent and insightful comments that were invaluable in improving the manuscript.

Declaration of interest

IC and YN are employees of Cabot Corporation and Orion Engineered Carbons, respectively, both of which are carbon black manufacturing companies. IC, YN, and LL are members of the Scientific Advisory Group (SAG) to the ICBA (http://www.carbon-black.org) who funded this review paper. ICBA is a scientific, non-profit corporation originally founded in 1996. The purpose of the ICBA is to encourage and develop international communication, cooperation, and research concerning carbon black environmental, health, and safety matters and related regulatory matters. The ICBA is a seven member association of carbon black manufacturers with global operations and is funded by the member companies. LL and CF are both independent consultants to the SAG/ICBA. This review article was prepared during the course of employment (IC and YN) or as compensated consultants by SAG/ICBA (LL and CF). In the past 5 years, none of the authors have appeared in any legal or regulatory proceedings related to the content of the paper. The paper has not been reviewed by either in-house or outside legal counsel. The review, synthesis, and conclusions reported in this paper are the exclusive professional work product of the authors and may not necessarily represent the views of their employers or funding sources.