Thirdhand Smoke and More
The Indoor Environment Group has more than 20 years of experience in the characterization of tobacco smoke and its consequences for indoor air quality. We have carried out numerous studies to identify suitable environmental tracers, describe ventilation requirements, understand chemical reactions involving tobacco-related pollutants and contribute to assess exposure, health impacts and risk.
In recent and ongoing projects, we are investigating the composition and chemical transformations of residual constituents of tobacco smoke that linger indoors long after smoking ended (thirdhand smoke). Nicotine, the main alkaloid in tobacco, is emitted in the sidestream and exhaled mainstream smoke of cigarettes. It is a commonly used tracer for secondhand tobacco smoke (SHS), and its metabolite cotinine is a standard biomarker for SHS exposure. Our research showed that the dynamic behavior of nicotine differs from that of SHS particles and non-sorbing gases: it sorbs rapidly to and accumulates extensively in indoor materials, from where it desorbs to yield relatively high background concentrations in indoor air.
In addition to long-term, low-level re-emission of nicotine and other semivolatile SHS components from contaminated surfaces, the presence of significant nicotine deposits on indoor materials becomes a source of secondary pollutants formed from its reaction with atmospheric oxidants and nitrosating agents. We showed that reactions of nicotine and other SHS constituents with indoor ozone yields several oxidation byproducts that re-emit as gas-phase species or in ultrafine particles, and are often stronger asthmagens than their parent compound.
In a separate study, we also showed that nicotine reacts with nitrous acid to form carcinogenic tobacco-specific nitrosamines. These findings led to new studies currently underway to better understand the harm caused by exposure to thirdhand smoke through various routes (inhalation, dermal, ingestion). Our group is participating in a large collaborative research consortium that includes several California universities (UC San Francisco, UC Riverside, San Diego State University).