The study shows that exposure to secondhand smoke exceeds the estimated level of health risk.

The third secondhand smoke refers to residual nicotine and other hazardous chemicals that pollute the indoor environment after smoking, such as tobacco odors lingering in clothing and the home.

Scientists at the Lawrence Berkeley National Laboratory of the US Department of Energy first identified third-party secondhand smoke as a potential health risk ten years ago.

The lab’s latest study has quantified long-term health risks and found that concentrations of toxic chemicals suspended in cigarette-smoking rooms may exceed California risk guidelines, meaning that non-smokers may be at risk for health by living in polluted places. .

Berkeley Lab researchers previously found that volatile nicotine, which is released during smoking and e-vapour, is absorbed by interior surfaces, where it can react with a compound in indoor air called nitrous acid (HONO) to form potent carcinogens called nitrate-specific compounds. tobacco with nitrosamines. TSNA). Nicotine accumulated on household surfaces can continuously generate TSNA long after the smoke has cleared the room.

Experts say: “Since we first described this chemistry in 2010, numerous studies have demonstrated the presence of TSNA on indoor surfaces and in settled dust. People may be exposed to it while living in homes polluted with outside smoke.”

TSNAs enter the body through several routes, and the study evaluated dust inhalation and ingestion doses using indoor TSNA concentrations measured by the consortium researchers and other authors.

The team focused on skin exposures that are difficult to measure and about which much less information is available. These skin exposures can occur directly through skin contact with polluted air or a contaminated surface containing TSNA, such as while sleeping on smoky sheets, but they also can occur through skin chemistry when nicotine already on the skin reacts with the HONO environment to form TSNA directly on the surface of the body.

“Nicotine is released in large quantities during smoking, and it coats all indoor surfaces, including human skin,” said Xiaochen Tang, who led the experimental work at Berkeley Labs at the Indoor Environment Group. .”

This reaction produced three different TSNAs, two of which were abbreviated as NNK and NNN and are known carcinogens. There is less information on the toxicity of the third, NNA, which is not found in tobacco smoke, so the study included an assessment in vitro.

“We provided additional evidence for the genotoxicity of NNA by evaluating its effect on transplanted human lung cells,” said Pu Hang, co-author at the Berkeley Biosciences Lab, “the most harmful genetic toxins.”

To better understand the effects on the skin, researchers at UC Riverside and UC San Francisco assessed how NNK and nicotine penetrate the skin of mice.

Co-author Manuela Martins-Greene of the University of California, Riverside, noted that “Under the experimental conditions used, analysis of metabolites in mouse urine showed that for both compounds, direct skin contact results in accumulation and circulation in the body.” ., within seven days of cessation of skin exposure.

The study found that exposure through all of these pathways through inhalation, ingestion of dust, and absorption through the skin under typical indoor conditions could result in doses of NNK exceeding health guidelines known as “minor risk levels” set by the California Bureau of Environmental Health Risks. . Evaluation As part of Proposition 65, this cumulative exposure may contribute to a higher risk of cancer, and dermal routes of exposure greatly contribute to ingestion of TSNA at concentrations comparable to or even higher than those inhaled.

“Next steps of this study will explore in more detail the mechanisms of adverse health effects associated with tobacco and cannabis residues, effective treatment strategies, and the application of scientific findings to tobacco control practice,” says co-author Neil Benowitz, a professor at the University of California, San Francisco. . who leads the consortium.

Source: Medical Express

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