Characterization of trace metals in E-cigarettes

Abstract

Electronic cigarettes (e-cigarettes) are devices that are designed to replace conventional cigarettes (Hartmann-Boyce et al., 2021). E-cigarettes are electronic devices that heat a liquid to produce a vapour for inhalation by users. They were invented to provide smokers with a safer and cleaner way to inhale tobacco and to enable them to cease their smoking habit. These types of cigarettes are considered to be safer than conventional cigarettes because they do not contain harmful tobacco; however, like conventional cigarettes, most contain nicotine – which is toxic and addictive – and the presence of other hazardous components is inherent in their design (Gaur & Agnihotri, 2018). The e-cigarette liquids, atomisers and aerosols are major sources of trace heavy metals, also known as trace elements (TEs), which pose risks to human health at certain concentrations in the body. TEs such as tin (Sn), nickel (Ni), aluminium (Al), chromium (Cr) and cadmium (Cd) leak from the core assembly (Jaishankar et al., 2014), while others such as lead (Pb) and zinc (Zn) are present in the liquid. Although some of these metals are essential elements at low doses, they are toxic at high concentrations, especially when they are inhaled. They are potentially carcinogenic and have been linked to the development of fatal health problems such as anaemia (US Centers for Disease Control and Prevention [CDC], 2022). Thus, although e-cigarettes are characterised as safer than conventional cigarettes, they can still pose a threat to human health. When a user smokes a conventional cigarette, the harmful elements in tobacco smoke enter the user’s nervous system (heart and vital organs) within a few seconds of the initial inhalation and subsequently affect many parts of the body. However, inhalation of vapourised electronic cigarette liquid (e-liquid) is becoming increasingly popular. This vapour is generally considered safer than the contents of conventional cigarette smoke. The active components of e-cigarettes are mixtures of propylene glycol (PG) and vegetable glycerine (VG) that contain different proportions of nicotine and flavouring (Stratton et al., 2018). The two most harmful components of tobacco smoke, tar and carbon monoxide, are absent from e-cigarettes, which are subject to strict safety and quality regulations. However, e-cigarettes still pose risks because they are only slightly safer than conventional cigarettes (Uchiyama et al., 2020). This research project was designed to investigate the source of TEs in e-cigarettes. The identified sources included the metal cover, inner clamp and wick. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was utilised to determine the levels at which various elements were present in e-cigarette samples. ICP-MS in single particle mode was used to determine the presence of nanoparticles. Due to the solubility properties of the e-liquids, many e-cigarettes contain dissolved TEs, such as Ni, Pb and Zn. The concentrations of VG and PG vary according to the e-liquid brand, so the proportions of TEs vary among e-cigarettes. There is a close relationship between a high concentration of VG and a high amount of TEs in e-cigarettes. In this project, increased ratios of VG to PG resulted in increased concentrations of TEs in the e-liquids. Parameters of the e-cigarettes, such as power and number of puffs, were studied and were discovered to influence the concentrations of TEs found in the e-liquids.