Third-hand Smoke May Increase Long-Term Health Risks: Study

A research report from a team at Lawrence Berkeley National Laboratory states that dangerous chemicals and nicotine lingering indoors after smoking may pose significant long-term health risks for non-smokers.

A study has shown that living in environments polluted by smoke, whether it is handling the clothes of a smoker or staying in a hotel that allows smoking, can potentially lead to exposure to toxic chemicals that exceed current risk guidelines.

A research team conducted an experiment to investigate the risks of residual nicotine in the air after indoor smoking or e-cigarette use. The results revealed that the toxins from indoor exposure were absorbed by surfaces and reacted with another air-borne compound called nitrous acid (HONO). This combination produced carcinogenic compounds known as tobacco-specific nitrosamines (TSNA).

Even if the smoke appears clear, a microscopic view shows the accumulation of nicotine on household surfaces. The constant buildup of nicotine caused by repeated smoking leads to the formation of TSNA, increasing the risk of cancer and other health conditions for individuals.

Since our initial description of this chemical reaction in 2010, several studies have provided further evidence of the presence of TSNA and dust deposits on indoor surfaces. In this new article, we combine information from the past decade with our latest results to estimate the daily dosage that individuals may be exposed to when in homes contaminated by thirdhand smoke," explained chemist Hugo Destaillats of Berkeley Lab in a press release.

How do these chemicals enter the human body?

TSNA can enter the body through direct inhalation or ingestion of dust mixed with carcinogenic compounds. While not inevitable, evidence suggests that TSNA can also enter through contaminated air or surfaces via skin contact. For example, sleeping on sheets where someone has been smoking. Another method is through epidermal chemistry, where nicotine on the skin reacts with environmental HONO to form TSNA directly on the skin's surface.

According to Xiao Chen, a researcher at the Berkeley lab and the main author of the study, "Nicotine is released in large quantities during smoking and covers all indoor surfaces, including human skin." "We have found that compared to clean surfaces, the presence of skin oils and sweat on model surfaces leads to higher levels of TSNA production in the presence of HONO.

When measuring the dose of each potential TSNA pathway in the body, the researchers discovered the formation of three different TSNA, including two known carcinogens. One of them, labeled as NNA, is not present in tobacco smoke, and there is little information regarding its toxicity. Therefore, the focus of the study is on the two carcinogens, known as NNK and NNN.

Bo Hang, a co-author in the Biological Sciences Division of Berkeley Lab, stated, "We provide additional evidence of the genetic toxicity of NNA by evaluating its impact on cultured human lung cells. Exposure to NNA results in DNA damage, including double-strand breaks, which are the most harmful genetic toxic outcomes.

Researchers exposed NNK and NNN to the skin of mice, and urine analysis confirmed that metabolites of these compounds showed that they entered the body. Even after the team stopped exposing the mice to the carcinogens, metabolites continued to accumulate in their bodies for a week.

Entering through the skin is a major issue.

Research findings indicate that repeated exposure to tobacco smoke or electronic cigarettes can accumulate toxins in the body, increasing the risk of cancer. Skin exposure appears to be a more common pathway for people to come into contact with TSNA, potentially even more so than through smoking itself.

Neal Benowitz, a professor at the University of California, San Francisco, added: "These findings highlight the potential health effects of third-hand smoke, which not only contains TSNAs but also hundreds of other chemicals, some of which are known carcinogens." He further stated, "The next step in this research will be to explore in detail the mechanisms of the adverse health effects associated with tobacco and cannabis residue, effective remediation strategies, and translating scientific findings into tobacco control practices.

The research findings were published in the journal "Environmental Science and Technology.

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