A recent study published in Environmental Science & Technology suggests that tap water may be contaminated by cigarette smoke.
A group of researchers, including academics from the University of Alberta and water system experts from the Metropolitan Water District of Southern California, looked at tobacco-specific nitrosamines (TSNAs), which are thought to be found in water. These are present in cigarette smoke and have been proved to be carcinogenic. In their study, researchers suggested that TSNAs were also "a new class of disinfection byproducts," meaning that they could be discovered in water after they have been formed during the disinfection process.
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For their study, researchers sampled water from seven drinking water treatment plants and two wastewater treatment plants, testing for the presence of five different TSNAs. They simulated water disinfection through treating water with ammonia and chlorine and found that two of the TSNAs appeared in the samples only after treatment, suggesting that they were disinfection byproducts. A third type of TSNA was present before treatment but its levels were much higher after the process.
In conclusion, the researchers stated that there were precursors to the formation of TSNAs in water but it was the water disinfection process that triggered the formation and converted them into TSNAs.