Over the last years, the popularity of electronic e-cigarettes has increased significantly. An important contributor to this trend is the availability of a wide variety of flavours used in e-liquid refills. However, the role of these flavouring components in the potential toxicity of e-cigarette vapours remains unclear. Considering the large number of e-liquid flavours available on the market (> 7000), there is an urgent need to establish an efficient screening strategy to prioritize the substances of highest concern for human health. In this context, genotoxicity is a key (toxicological) endpoint as it is related to a broad range of adverse human health effects including cancer. Therefore, in this study, a prioritization strategy based on a combination of analytical screening, in silico prediction and literature consultation was developed for identifying potentially genotoxic substances in e-liquid flavours.

77 e-liquids, representative for the different flavour categories, were collected on the Belgian market and screened for their chemical composition using GC-MS. By using the National Institute of Standards and Technology (NIST) research library, 436 individual components could be identified. Next, the genotoxic potential of these individual components was investigated in silico with two complementary (quantitative) structure-activity relationship ((Q)SAR) models (Derek Nexus, Sarah Nexus). In total, 57 flavouring components were identified with a structural alert for genotoxicity in at least one of the two (Q)SAR models. For these substances, genotoxicity data was collected from previous European safety evaluations in different regulatory domains (e.g. by the European Chemical Agency (ECHA) and the European Food Safety Authority (EFSA)). Genotoxicity could be excluded for only 12 of the 57 components, whilst for 2 of them there is a clear concern for genotoxic potential. Data for the remaining components was missing or ambiguous and hence additional toxicological data is required in order to be able to exclude genotoxic potential.

The above findings indicate that the use of flavoring components might thus pose a potential health risk for e-cigarette users. Further research might explore to which extent these flavouring substances are transferred from the e-liquid into the e-cigarette vapours.