Washington, Feb 9 (ANI) : A new study has shown that the residue from tobacco smoke that clings to virtually all surfaces long after a cigarette has been extinguished could prove to be a potential health hazard.

The research team at Lawrence Berkeley National Laboratory (Berkeley Lab) showed that nicotine in third-hand smoke reacts with the common indoor air pollutant nitrous acid to produce dangerous carcinogens.

"The burning of tobacco releases nicotine in the form of a vapour that adsorbs strongly onto indoor surfaces, such as walls, floors, carpeting, drapes and furniture," said Hugo Destaillats, a chemist with the Indoor Environment Department of Berkeley Lab''s Environmental Energy Technologies Division.Nicotine can persist on those materials for days, weeks and even months.

The study shows that when this residual nicotine reacts with ambient nitrous acid it forms carcinogenic tobacco-specific nitrosamines or TSNAs.

These TSNAs are one of the most broadly acting and potent carcinogens present in unburned tobacco and tobacco smoke.

The authors report that in laboratory tests using cellulose as a model indoor material exposed to smoke, levels of newly formed TSNAs detected on cellulose surfaces were 10 times higher than those originally present in the sample following exposure for three hours to a "high but reasonable" concentration of nitrous acid (60 parts per billion by volume).

Unvented gas appliances are the main source of nitrous acid indoors.

Since most vehicle engines emit some nitrous acid that can infiltrate the passenger compartments, tests were also conducted on surfaces inside the truck of a heavy smoker, including the surface of a stainless steel glove compartment.

These measurements also showed substantial levels of TSNAs. In both cases, one of the major products found was a TSNA that is absent in freshly emitted tobacco smoke - the nitrosamine known as NNA. The potent carcinogens NNN and NNK were also formed in this reaction.

"Given the rapid sorption and persistence of high levels of nicotine on indoor surfaces, including clothing and human skin, our findings indicate that third-hand smoke represents an unappreciated health hazard through dermal exposure, dust inhalation and ingestion," said lead author Mohamad Sleiman.

Third-hand smoke would pose the greatest hazard to infants and toddlers.

"Residues follow a smoker back inside and get spread everywhere. The biggest risk is to young children. Dermal uptake of the nicotine through a child''s skin is likely to occur when the smoker returns and if nitrous acid is in the air, which it usually is, then TSNAs will be formed," said Lara Gundel, one of the study authors.

"Nicotine, the addictive substance in tobacco smoke, has until now been considered to be non-toxic in the strictest sense of the term," said Kamlesh Asotra of the University of California''s Tobacco-Related Disease Research Program, which funded this study.

"What we see in this study is that the reactions of residual nicotine with nitrous acid at surface interfaces are a potential cancer hazard, and these results may be just the tip of the iceberg," Asotra added.

The findings appear in Proceedings of National Academy of Sciences.