Alongside Berkeley Lab scientists, co-authors on this work embody collaborators from the University of California San Francisco, the University of California Riverside and San Diego State University. These groups are members of the California Consortium on Thirdhand Smoke, funded by the Tobacco-Related Disease Research Program, which is managed by the University of California.
Berkeley Lab’s researchers beforehand found that aerosolized nicotine, launched throughout smoking and vaping, adsorbs to indoor surfaces, the place it will probably work together with a compound current in indoor air known as nitrous acid (HONO) to type strongly carcinogenic compounds known as tobacco-specific nitrosamines (TSNAs). Accumulated nicotine on family surfaces can repeatedly generate TSNAs, lengthy after smoke clears the room.
“Since we first described this chemistry in 2010, several studies have further illustrated the presence of TSNAs on indoor surfaces and settled dust. In this new article, we integrated the new information produced over the past decade with our most recent results, to estimate the daily doses to which people may be exposed when living in homes contaminated with thirdhand smoke,” mentioned Berkeley Lab chemist Hugo Destaillats, the examine’s principal investigator.
TSNAs enter the physique by means of a number of pathways. The examine estimated doses by means of inhalation and dust ingestion utilizing TSNA indoor concentrations measured by Consortium investigators and different authors. In addition, the crew centered on dermal exposures, that are tougher to measure, and for which there’s a lot much less info. These dermal exposures can occur straight by means of pores and skin contact with polluted air or a contaminated floor harboring TSNAs – for instance, whereas sleeping on smoky mattress sheets. But they will additionally happen through epidermal chemistry, when nicotine already settled on the pores and skin reacts with environmental HONO to type TSNAs proper on the physique’s floor.
“Nicotine is released in large amounts during smoking, and it coats all indoor surfaces, including human skin,” mentioned Xiaochen Tang, who led Berkeley Lab’s experimental efforts within the Indoor Environment Group. “We found that the presence of skin oils and sweat on model surfaces led to a higher yield of TSNAs in the presence of HONO, compared with clean surfaces.”
Three totally different TSNAs had been shaped on this response, two of which (recognized by the acronyms NNK and NNN) are recognized carcinogens. There is much less toxicological info for the third one, NNA, which isn’t current in tobacco smoke. For that purpose, the examine included an in vitro evaluation.
“We present additional evidence of the genotoxicity of NNA by evaluating its effect on cultured human lung cells,” mentioned Bo Hang, a co-author from Berkeley Lab’s Biosciences Area. “Contact with NNA led to DNA damage, including double-strand breaks, the most deleterious genotoxic outcome.”
To higher perceive dermal exposures, Consortium researchers at UC Riverside and UC San Francisco evaluated how NNK and nicotine penetrate by means of the pores and skin of mice. Co-author Manuela Martins-Green, of UC Riverside, identified that “under the experimental conditions used, the analysis of the metabolites in the mouse urine showed that, for both compounds, direct dermal contact resulted in the accumulation and circulation in the body for seven days after dermal exposure was discontinued.”
The examine discovered that publicity by means of all of those pathways – inhalation, dust ingestion, and dermal absorption – beneath typical indoor circumstances can lead to NNK doses that exceed well being tips often called “No-Significant Risk Levels” established by California’s Office of Environmental Health Hazard Assessment as a part of Proposition 65. These cumulative exposures can contribute to an elevated most cancers danger. Dermal publicity routes contribute considerably to TSNA consumption at ranges that may be similar to and even increased than inhalation.
“These findings illustrate the potential health impacts of thirdhand smoke, which contains not only TSNAs but hundreds of other chemicals, some of which are also known carcinogens,” mentioned co-author Neal Benowitz, a UCSF professor who leads the Consortium. “Next steps for this research will explore in more detail the mechanisms of adverse health effects associated with tobacco and cannabis residues, effective remediation strategies, and translation of scientific findings to tobacco control practice.”
This examine was funded by the UC Tobacco-Related Diseases Research Program.