New Ways to Measure Thirdhand Smoke Exposure

A recent study by researchers at International University of Catalonia, Catalan Institute of Oncology, and the Bellvitge Biomedical Research Institute used survey responses and saliva samples to try to distinguish between second- and thirdhand smoke exposure.

Feb 3, 2021

By: Leta Dickinson

Thirdhand smoke: nearly impossible to completely remove, often undetectable to our eyes or noses, and with chemical residue that has health consequences for us and our loved ones. This persistent residue of tobacco smoke pollutant presents a challenge to public health officials and researchers alike because it is difficult to determine the extent of exposure, particularly when it comes to distinguishing thirdhand smoke exposure from secondhand smoke exposure. After all, secondhand smoke is the precursor of thirdhand smoke and both can occur simultaneously in our homes, cars, public spaces, hotels, and more, with or without our noticing.
Researchers from Barcelona (Spain) recently published new research that tried to investigate how thirdhand smoke exposure compares to secondhand smoke exposure. The researchers surveyed over 500 residents of Barcelona, Spain about their self-reported exposure to second- and thirdhand smoke before testing a saliva sample for chemical markers of tobacco.
The questions in the survey were used to categorize participants, all of whom were nonsmokers, into one of three categories: “not exposed,” “only thirdhand smoke exposed,” and “second- and thirdhand smoke exposed.” To determine which category each participant fell in, they were asked questions about smoking rules within their home and how many cigarettes were smoked in their presence in the last week.
Then, the researchers collected a saliva sample from each participant to test for a compound uniquely associated with tobacco, called cotinine. Cotinine is a biomarker, or a measurable indicator, of recent tobacco exposure. The higher the levels of cotinine, the higher the levels of exposure to nicotine in the past few days. They measured the levels of cotinine in the saliva samples and compared the values for each of the three groups.
The researchers found that those in the “no exposure” group had the lowest levels of cotinine, while the “only thirdhand smoke exposed” and “second- and thirdhand smoke exposed” groups had about the same cotinine levels, indicating the hazards of thirdhand smoke exposure should be taken as seriously as those of secondhand smoke.
Other studies have shown that nonsmokers can be exposed to toxic tobacco residue even if there is no secondhand smoke. But important research still needs to be conducted to better distinguish between “not exposed”, “only thirdhand smoke exposed”, and “second- and thirdhand smoke exposed”. Using self-reports to categorize participants into “not exposed” and “only thirdhand smoke exposed” relies on their own awareness of exposure and is likely to lead to misclassification. In communities with historically high levels of indoor smoking, large reservoirs of thirdhand smoke may be present in indoor environments years after smoking has stopped. Nonsmokers may not be aware of the toxic tobacco residue that persists on surfaces and in house dust.
Important research also needs to be done on biomarkers of exposure to better distinguish between secondhand and thirdhand smoke. Cotinine levels measure the exposure to nicotine but cannot determine whether it comes from secondhand or thirdhand smoke. Instead, new biomarkers are needed that will allow researchers to tell the difference between inhaled secondhand smoke and exposure to thirdhand smoke via touching, ingesting, and inhaling residue from the environment.
As we learn more about the widespread exposure of nonsmokers to thirdhand smoke residue at home, researchers need to develop new methods to carefully distinguish exposure to thirdhand smoke from exposure to secondhand smoke.

Click here to read the research study.

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