Third-hand smoke warning

Most of us are aware of the dangers of second-hand smoke, but now scientists are warning that the nicotine present in third-hand smoke can react with a common air pollutant and form cancer causing chemicals.

Third-hand smoke is the name given to the residue from tobacco smoke that clings to the surfaces of a room, giving it a stale or musty smell.

"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 chemist Hugo Destaillats from the Lawrence Berkeley National Laboratory, California.

"Nicotine can persist on those materials for days, weeks and even months," he added.

Tests done by the scientists showed that when nicotine in third-hand smoke comes into contact with a common air pollutant - nitrous acid - tobacco specific nitrosamines or TSNAs are formed on surfaces at ten times the concentration found in the original smoke.

"TSNAs are among the most broadly acting and potent carcinogens present in unburned tobacco and tobacco smoke," said Destaillats.

People may be exposed to TSNAs by inhaling dust or coming into contact with contaminated carpet or clothing. The scientists warned that young children are particularly at risk from third-hand smoke as they are more likely to lick surfaces.

Asking a smoker to smoke outside does not get rid of the problem either, said study co-author Lara Gundel.

"Smoking outside is better than smoking indoors but nicotine residues will stick to a smoker's skin and clothing," she says.

"Those 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."

The scientists are now carrying out further studies to find out how long the TSNAs remain stable indoors and what other chemicals are produced when third-hand smoke reacts with nitrous acid.

"We know that these residual levels of nicotine may build up over time after several smoking cycles, and we know that through the process of aging, third-hand smoke can become more toxic over time," says Destaillats.

"Our work highlights the importance of third-hand smoke reactions at indoor interfaces, particularly the production of nitrosamines with potential health impacts," he concluded.

This article was published on Tue 9 February 2010