Abstract

Objectives: The objectives of this study were: to characterise the exposure of non-smokers exposed to secondhand smoke in a vehicle using biomarkers, to describe the time course of the biomarkers over 24 h, and to examine the relationship between tobacco biomarkers and airborne concentrations of SHS markers. Methods: Eight non-smokers were individually exposed to SHS in cars with fully open front windows and closed back windows over an hour from a smoker who smoked three cigarettes at 20 min intervals. The non-smokers sat in the back seat on the passenger side, while the smoker sat in the driver's seat. Plasma cotinine and urine cotinine, 3-hydroxycotinine and 4- --1-butanol were compared in samples taken at baseline and several time-points after exposure. Nicotine, particulate matter and carbon monoxide were measured inside and outside the vehicle and ventilation rates in the cars were measured. Results: Average plasma cotinine and the molar sum of urine cotinine and 3HC increased four-fold, urine cotinine increased six-fold and urine NNAL increased ~7 times compared to BL biomarker levels. Plasma cotinine, urine COT+3HC and NNAL peaked at 4-8 h post-exposure while urine cotinine peaked within 4 h. Plasma cotinine was significantly correlated to PM2.5 and CO but not to air nicotine. The correlations between urine biomarkers, cotinine, COT+3HC and NNAL, and air nicotine, PM2.5 and CO were moderate but nonsignificant. Conclusions: Brief SHS exposure in cars resulted in substantial increases in levels of tobacco biomarkers in non-smokers. For optimal characterisation of SHS exposure, tobacco biomarkers should be measured within 4-8 h post-exposure. Additional studies are needed to better describe the relationship between tobacco biomarkers and environmental markers of SHS.