Rebekah Eliason for redOrbit.com – Your Universe Online
For the first time ever, thirdhand smoke has been found to cause significant amounts of damage to human cells. Thirdhand smoke is the toxic residue that attaches to almost all surfaces leaving a strong odor long after cigarette smoke has dissipated.
The researchers from Lawrence Berkeley National Laboratory also discovered in this study that chronic exposure caused more DNA damage than acute exposure. Samples exposed to chronic thirdhand smoke contained higher concentrations of chemical compounds than samples exposed to acute third-hand smoke. This suggests that as the smoke residue sits it becomes more harmful over time.
“This is the very first study to find that thirdhand smoke is mutagenic,” explained Lara Gundel, a Berkeley Lab scientist and co-author of the study. “Tobacco-specific nitrosamines, some of the chemical compounds in thirdhand smoke, are among the most potent carcinogens there are. They stay on surfaces, and when those surfaces are clothing or carpets, the danger to children is especially serious.”
Researchers tested DNA damage for genotoxicity by using two common in vitro assays known as the Comet assay and the long amplicon-qPCR assay. In vitro assays are laboratory tests which are performed in a test tube to measure the activity of a drug or compound. The tests found that samples tested positive for genotoxicity with both DNA strand breaks as well as oxidative DNA damage. Genotoxicity of this nature is associated with gene mutation which possibly leads to many types of cancer caused by smoking and secondhand smoke exposure.
“Until this study, the toxicity of thirdhand smoke has not been well understood,” explained lead researcher Bo Hang. “Thirdhand smoke has a smaller quantity of chemicals than secondhand smoke, so it’s good to have experimental evidence to confirm its genotoxicity.”
In 2010 Berkeley Lab studies found residual nicotine can react with ozone and nitrous acid which are common indoor air pollutants that form hazardous compounds. The nicotine left in thirdhand smoke reacts with nitrous acid and undergoes a chemical reaction that forms tobacco-specific carcinogenic nitrosamines. When nicotine reacts with ozone, ultrafine particles are formed that can pass through human tissue and carry harmful chemicals with them. People can be exposed to dangerous thirdhand smoke residue through inhalation, ingestions or skin contact.
Thirdhand smoke is especially dangerous because it is extremely difficult to eliminate. Studies found that even two months after smokers moved out of an apartment, smoke particles can be detected in dust. Normal cleaning techniques such as ventilation and vacuuming have not been shown to lower nicotine contamination.
“You can do some things to reduce the odors, but it’s very difficult to really clean it completely,” said Destaillats. “The best solution is to substitute materials, such as change the carpet, repaint.”
This study was performed by placing paper strips in smoking chambers. One set was placed in the chamber for twenty minutes to simulate acute exposure and the second set was placed in a chamber for 258 hours over the span of 196 days to simulate chronic exposure. During the 196 days, the chamber was ventilated for approximately 35 hours.
Researchers discovered higher concentrations of toxic chemicals in the chronically exposed samples for over half the compounds studied when compared with acutely exposed samples. DNA damage was also more extensive in chronic samples.
“The cumulative effect of thirdhand smoke is quite significant,” Gundel said. “The findings suggest the materials could be getting more toxic with time.”
Hang and his teammate’s first extracted compounds from the paper strips using a culture medium that was used to expose human cells for 24 hours. Concentrations of each of the compounds were carefully measured.
“They are close to real-life concentrations, and in fact are on the lower side of what someone might be exposed to,” Hang said.
Hang intends to continue his research by understanding how the chemical reaction between the nitrous amine NNA and different DNA bases works. NNA is important because it is a tobacco-specific nitrous amine not found in secondhand smoke. “It looks like it’s a very important component of thirdhand smoke, and it is much less studied than NNK and NNN in terms of its mutagenic potential,” Hang explained.
Researchers concluded that “Ultimately, knowledge of the mechanisms by which thirdhand smoke exposure increases the chance of disease development in exposed individuals should lead to new strategies for prevention.”
This study “Thirdhand smoke causes DNA damage in human cells” is published in the journal Mutagenesis. The lead investigator was Bo Hang, a biochemist in the Life Sciences Division of Berkeley Lab. He worked with an interdisciplinary group, including chemists from Berkeley Lab’s Environmental Energy Technologies Division Lara Gundel, Hugo Destaillats and Mohamad Sleiman as well as scientists from UC San Francisco, UCLA Medical Center and the University of Texas.
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