Exposure to secondhand and thirdhand smoke in private vehicles: Measurements in air and dust samples

This study aimed to estimate airborne nicotine concentrations and nicotine, cotinine, and tobacco-specific nitrosamines (TSNAs) in settled dust from private cars in Spain and the UK.

We measured vapor-phase nicotine concentrations in a convenience sample of 45 private cars from Spain (N = 30) and the UK (N = 15) in 2017-2018. We recruited non-smoking drivers (n = 20), smoking drivers who do not smoke inside the car (n = 15), and smoking drivers who smoke inside (n = 10). Nicotine, cotinine, and three TSNAs (NNK, NNN, NNA) were also measured in settled dust in a random subsample (n = 20). We computed medians and interquartile ranges (IQR) of secondhand smoke (SHS) and thirdhand smoke (THS) compounds according to the drivers' profile.

24-h samples yielded median airborne nicotine concentrations below the limit of quantification (LOQ) (IQR: 3 (IQR:0.18-0.45) in cars of smokers not smoking inside, and 3.53 μg/m³, (IQR:1.74-6.38) in cars of smokers smoking inside (p < 0.001). Nicotine concentrations measured only while travelling increased to 21.44 μg/m³ (IQR:6.60-86.15) in cars of smokers smoking inside. THS concentrations were higher in all cars of smokers, and specially in cars of drivers smoking inside (nicotine: 38.9 μg/g (IQR:19.3-105.7); NNK: 28.5 ng/g (IQR:26.6-70.2); NNN: 23.7 ng/g (IQR:14.3-55.3)), THS concentrations being up to six times those in non-smokers' cars.

All cars of smokers had measurable SHS and THS pollution, the exposure levels markedly higher in vehicles of drivers where smoking took place. Our results evidence the need for policies to prohibit smoking in vehicles, but also urge for more comprehensive strategies aiming towards the elimination of tobacco consumption.