Electronic cigarette (e-cigarette) use is known to emit toxic chemicals and deteriorate outdoor and indoor air quality. Home is a place where e-cigarette users may frequently use their devices amid increasing prohibition of e-cigarette use in public places. This study aims to assess the real-life scenario of bystanders' exposure to secondhand e-cigarette aerosol (SHA) at home. A one-week observational study was conducted in four countries (Greece, Italy, Spain, and the United Kingdom) in 2019 including:
1) homes of e-cigarette users living together with a non-user/non-smoker; and
2) control homes with no smoker nor e-cigarette user. Indoor airborne nicotine and PM2.5 concentrations were measured as environmental markers of SHA, as well as concentrations of biomarkers, including nicotine and its metabolites, tobacco-specific nitrosamines, propanediol, glycerol, and metals in participants' saliva and urine samples.
E-cigarette use characteristics, such as e-liquid's nicotine concentration, e-cigarette types, place of e-cigarette use at home, and frequency of room ventilation, were also collected. A total of 29 e-cigarette users' homes and 21 control homes were included. The results showed that the levels of seven-day airborne nicotine were quantifiable in 21 (72.4%) out of 29 e-cigarette users' homes; overall they were low (median: 0.01 µg/m3) but significantly higher than those found in control homes (p=0.010). Concentrations of seven-day PM2.5 in e-cigarette and control homes were similar. Airborne nicotine and PM2.5 concentrations did not differ according to different e-cigarette use conditions. Non-users residing with e-cigarette users had low but significantly higher levels of nicotine, cotinine, 3'-OH-cotinine, and 1,2-propanediol in saliva, and cobalt in urine than non-users living in control homes. In conclusion, e-cigarette use at home created bystanders' exposure to SHA regardless of the conditions of use. We recommend the inclusion of e-cigarettes in smoke-free home rules to protect bystanders from any exposure to SHA.