Measurement of SHS
The most direct and widely used method to measure ETS exposure is personal monitoring of respirable suspended particles and nicotine. Respirable suspended particles and nicotine give a good indication of cumulative exposure over a relatively short period of time. However, they have considerable limitations because of duration of measurements, representativeness of activity and cost.
Particulate matter, or PM, is the term given to the tiny particles of solid or semi-solid material found in the atmosphere. It consists of varying combinations of dry solid fragments, solid cores with liquid coatings and small droplets of liquid. In the case of airborne particles, the initial sizes of particles produced by cigarette smoking have been quoted to be 0.3–1.0 μm. This figure is not universally accepted, however: sidestream smoke particle size has been said to be typically 0.01–1.0 μm, with mainstream smoke particle size ranging from 0.1–1.0 μm.
Photometers, optical particle counters (OPCs) and condensation particle counters (CPCs) measure airborne particles in real time. Each technology has a unique sensitivity to specific particle characteristics such as size, mass and refractive index.
The instruments most commonly used for PM measurements are the Met One Aerocet 531 aerosol particulate profiler (Met One Instruments) and the TSI SidePak AM510 condensation particle profiler (TSI).
Nicotine vapour can be collected on filters by passive samplers and analysed using gas chromatography/mass spectrometry (GC/MS). Concentrations as low as 0.01 μg·mL-1 can be detected.
Biomarkers are also useful for determining exposure to ETS because they enable us to predict potential health risks for exposed individuals, increasing our understanding of tobacco-related cancer mechanisms. Biomarkers offer a way to avoid many sources of bias or inaccurate reporting by study participants.
The most specific markers of exposure to SHS are thiocyanate and nicotine (in saliva, plasma or urine), and cotinine, a nicotine metabolite (in saliva, plasma, urine or hair). Cotinine is currently considered the marker of choice as thiocyanate is also influenced by diet, whereas cotinine appears to be the most specific and sensitive biomarker for smokers and nonsmokers as it reflects exposure to nicotine, which is almost wholly specific to tobacco.
Carboxyhaemoglobin in blood and carbon monoxide in exhaled air are also relatively easy-to-measure markers to quantify tobacco exposure, but they are not specific – road traffic or domestic emissions can affect them. Other substances that can be measured with more difficulty and variable specificity include: adducts of 4-aminobiphenyl to haemoglobin in red blood cells; adducts of benzo[a]pyrene to DNA in white blood cells; adducts of polycyclic aromatic hydrocarbons (PAHs) to plasma albumin; nicotine- derived nitrosamines in urine; hydroxyproline in urine; and n-nitrosoproline in urine.