Thirdhand smoke is the toxic residue from tobacco smoke that lingers on surfaces and in dust long after smoking has stopped. It is increasingly recognized as a persistent indoor pollutant. A recent study published in the academic journal Chemosphere adds to this growing body of evidence, showing that thirdhand smoke may be a significant and underrecognized source of toxic heavy metals in homes. Exposure to heavy metals, such as lead, arsenic, and cadmium, damages cells in the body and can interfere with healthy organ function.
The study was led by Dr. Nicolas Lopez-Galvez, an assistant professor in the School of Public Health at San Diego State University. Dr. Lopez-Galvez is a member of the Thirdhand Smoke Resource Center and an investigator at the Center for Tobacco and the Environment. His research examines how tobacco smoke residues persist in indoor environments and contribute to environmental exposures, particularly among vulnerable populations, including children and older adults.
The present study drew on a large database of samples collected through a collaboration with Dr. Melinda Mahabee-Gittens at Cincinnati Children’s Hospital and the University of Cincinnati. These samples all came from homes that had children, ranging in age from infants to 11 years. As part of data collection, parents and caregivers provided information on household smoking behaviors, whether smoking occurred indoors, and housing characteristics, including the age of the home. Children provided hand wipe and saliva samples for analysis of thirdhand smoke markers such as nicotine and cotinine, and dust samples collected from participants’ homes were analyzed in the environmental chemistry lab of Dr. Eunha Hoh at San Diego State University.
“What made this approach different,” Dr. Lopez-Galvez noted, “was the ability to examine thirdhand smoke markers and toxic metals together in a large sample while also controlling for factors we already know influence indoor contamination with tobacco smoke residue.”
In analyses of dust samples from 179 of the homes, all had detectable lead levels. Levels of lead, cadmium, and arsenic were strongly correlated with nicotine in household dust, a marker of thirdhand smoke. Importantly, these associations remained highly significant even after researchers controlled for sociodemographic factors such as income, race, and housing age.
“This was important because older homes are already known to have higher lead levels from sources such as lead-based paint or pipes,” Dr. Lopez-Galvez said. “Even after accounting for those factors, tobacco smoke residue still emerged as a major contributor to metal contamination in dust.”
Using statistical models, the researchers projected that homes free of tobacco smoke pollution could experience substantial reductions in toxic metals, including 87% less lead, along with 49% less cadmium and 38% less arsenic. These findings suggest that tobacco smoke residue may play a larger role in indoor metal exposure than previously recognized.
According to Dr. Lopez-Galvez, the results are especially useful for people living in lower-income or marginalized communities, including those in older homes or multi-unit housing where exposure to second- and thirdhand smoke residue may be more common. Children who spend more time close to floors and engage in frequent hand-to-mouth behaviors are especially vulnerable.
“There has been a long-standing focus on reducing toxic metals in homes through measures such as lead paint abatement and plumbing improvements,” Dr. Lopez-Galvez said. “Those efforts are important, but what has received far less attention is the role of thirdhand smoke as a persistent source of the same metals indoors.”
Dr. Lopez hopes the findings encourage policymakers and housing officials to broaden their thinking about indoor environmental health. Dr. Lopez-Galvez notes that if the goal is to reduce toxic metal exposure in homes, stronger smoke-free housing policies and more comprehensive approaches to eliminating thirdhand smoke residue need to be part of that conversation, particularly in homes with children.
Click here to read the full study in Chemosphere.
