Measurements of tar, nicotine and carbon monoxide levels in Australian cigarettes are assessed by machine under laboratory conditions, and have been published periodically by the federal government. Because people do not smoke a cigarette in the same way as a machine, the levels obtained by these means do not necessarily represent the levels ingested by the smoker. Tobacco companies use a number of manufacturing techniques to reduce machine measured delivery of noxious substances, including the use of perforations or air holes in the filter tip. The perforations, which are intended to dilute inhaled smoke, are not blocked when cigarettes are 'smoked' by machine, but can be occluded by the smoker's lips or fingers. This is likely to reduce any advantage they might have afforded. Recent research has shown that if half the perforations on a low tar (4mg) cigarette are blocked, a smoker could inhale up to three times more tar than indicated in published listings, and if all the holes are fully blocked, up to eight times more. Smoked in this way, a so-called low yield cigarette may produce between 6-10 mg of tar. That is a yield that could expected from a middle-of-the-range cigarette.(36) Individual smoking behaviour (for example, more frequent inhalation) also introduces wide variation into measurements of actual substance intake (see also Chapter 5, Section 3).
The accurate measurement of substance ingestion by smokers would require expensive and invasive personal sampling (for example, of nicotine levels present in blood or urine). This degree of testing is not justifiable, and although potentially misleading, the machine-generated results at least provide some guide to changes in delivery of the key noxious substances under standardised conditions. The estimates below are made with these known reservations.
Over the past decade men received higher average tar, nicotine and carbon monoxide exposure than women (Table 2.12). Men have probably always had a higher exposure to these constituents of tobacco smoke, due to their higher daily consumption of cigarettes than women (see Table 2.5 above), and because they tend to smoke higher tar cigarettes than women.(9,26) In 1989, the average tar content of cigarettes smoked by men was 9.3 mg, compared to 8.4 mg for women.(9)
Table 2.12 shows that mean daily tar exposure is declining for both sexes. This reflects the trend towards lower tar content in cigarette brands, and a move to lower tar brands among smokers. Combined with falling prevalence rates, this directly affects lung cancer death rates (see Chapter 3, Section 2). For further information on changes in tar content over time, refer to Chapter 5, Section 3.
The trend for nicotine exposure over time is not as clear as that for tar. Table 2.13 shows that daily nicotine consumption rose for both sexes, particularly women, during the early eighties, but now appears to be in decline. The apparent increase in mean daily nicotine exposure between 1980 and 1983 may be due to manipulation in cigarette engineering referred to above.
Daily exposure to carbon monoxide has declined steadily over the survey period (Table 2.14).