Third-hand smoking: indoor measurements of concentration and sizes of cigarette smoke particles after resuspension.

In a previous study1 of ‘secondhand’ cigarette smoke, we showed that 75% of the particles added to indoor air were of ultrafine sizes and had a half-life in air of 18 minutes at 25°C. These particles after their deposition on household surfaces could be later put back in suspension and constitute a toxic ‘thirdhand’ smoke2 which has not, as yet, been documented through quantitative data. Consequently, we undertook direct measurements of the concentration and sizes of smoke particles after their deposition and resuspension in a closed room.

A smoking device burned 10 cigarettes in 30 minutes in a non-ventilated furnished room that was then kept closed. On the next day, for particle resuspension, we mobilised the dust on furniture, clothes and surfaces by wiping and shaking and created even more turbulence with a ventilator.

An impactor (ELPI) measured the particle sizes (between 0.28 μm and 10 μm) and concentration in the air, 60 cm above the floor:

on the first day before and after the cigarettes were smoked (secondhand smoke) then 4 hours later.

24 hours later, before and after resuspension manoeuvres (thirdhand smoke).

Median diameter, concentration in number and mass of particles were respectively:

0.18 μm, 1.31.106.ml −1 and 15.4 mg.m−3 after smoking

0.30 μm, 0.98.104.ml−1 and 0.62 mg.m−3 4 hours later

0.07 μm, 1.66.102.ml−1 and 0.05 mg.m−3 1 day later.

0.15 μm, 0.92.104.ml−1 and 0.50 mg.m−3 1 day later after resuspension manoeuvres.

This showed that after cigarette smoking:

the airborne particles were of ultrafine sizes.

their concentration was divided by 100 in the first 4 hours and again by 100 in the following 24 hours. After resuspension, the concentration was multiplied by 100, going back to that observed 4 hours after smoking. This rise can only be attributed to particles smaller than 0,3 μm since other measurements made after resuspension manoeuvres without previous smoking only increased the concentration of particles over 0.3 μm of size.

These quantitative data support the hypothesis of a resuspension from the cigarette smoke surface contamination. However, this airborne contamination through resuspension remains much lower (100 times) than that of secondhand smoke. The rest of the aerosol mass initially produced by cigarettes could be firmly attached either to surfaces, leading to ingestion hazards and dermal transfer or to household dust and be inhaled with it.3 4

This study is the first to investigate the hypothesised resuspension of deposited particles of tobacco smoke (‘thirdhand smoke’).