Product modification.

For more than 20 years there has been a coherent programme of product modification in the UK, involving the introduction of low tar brands of cigarettes and the gradual reduction in average tar yields over the whole range of manufactured cigarettes. The sales-weighted average tar yield has declined from 20.8 mg/cigarette in 1972 to 11.0 mg/cigarette in 1993. To some extent potential benefits to established smokers have been offset by their tendency to 'compensate' for reduced nicotine yields. Investigating such aspects has formed one part of a wide-ranging research programme to monitor effects of modified products on health. Collectively the studies show benefits in terms of smoke intake and health outcome related to reduced tar cigarettes, but the success achieved in reducing average tar yields and narrowing the range has limited opportunities to detect differential effects.

60 years of chemical carcinogens: Sir Ernest Kennaway in retirement.

1992 marks the sixtieth anniversary of the publication of the first paper on the production of cancer by pure hydrocarbons, by the team at the Chester Beatty Research Institute headed by Professor Kennaway. Studies on polycyclic aromatic hydrocarbons and other chemical carcinogens continued to thrive under his leadership in succeeding years at the Chester Beatty and beyond, into his 'retirement' in 1946. He played a key role in stimulating research on factors contributing to the epidemic of lung cancer that became apparent by then, and with the support of the Medical Research Council (MRC) and other organizations he directed a small team working on analytical and epidemiological studies in a makeshift laboratory at St Bartholomew's Hospital. Published work included the identification and determination of benzo(a)pyrene in domestic soot, urban air pollution, motor vehicle exhausts and cigarette smoke, also arsenic in urban air and cigarette smoke, radon in indoor air and carbon deposits in human lungs. Such studies have been pursued in other laboratories around the world since then, and many of the lines of enquiry are traceable back to the pioneering work of the team at the Chester Beatty 60 years ago.

Air pollution in a city street. 1965.

Measurements of the concentrations of smoke, lead, and five polycyclic hydrocarbons in the air have been made in the City of London in the middle of a busy street and at two control sites. Samples were taken only throughout the daytime hours on weekdays to enable us to assess the maximum contribution made by traffic to the pollution in the street. The results showed that during these periods the air in the middle of the street contained three times as much smoke, four times as much lead, and 1.7 times as much 3:4-benzpyrene as were present in the general atmosphere as the City of London as estimated from samples taken at the control sites. One of these sites was chosen because it was only 150 feet away from the street; analyses yielded no evidence that the traffic contributed to the pollution sampled there. Sulphur dioxide concentrations were determined in the early part of the study and the results showed that traffic appeared to add little to the background level. The concentrations of lead found were below those held to be safe by many authorities. Carbon monoxide concentrations, reported in greater detail elsewhere, sometimes reached the accepted industrial maximum allowable concentration of 100 p.p.m.

Yields of tar and other smoke components from UK cigarettes.

Since 1972, regular six-monthly surveys of cigarettes on sale in the UK have determined the yields of tar, nicotine and carbon monoxide in mainstream smoke. During 1983-1990, a series of special studies investigated the yields of a range of additional analytes and their inter-relationships with the routinely monitored components. The results for total cyanide (as hydrogen cyanide), total aldehydes (including acetaldehyde), acrolein, formaldehyde and nitrogen monoxide are summarized, and the full data for six low-molecular weight phenols and three polycyclic aromatic hydrocarbons (PAHs) are reported. It is concluded that with the exception of nitrogen monoxide, which is strongly dependent upon the type of tobacco, and the delivery of some phenols and PAHs, which may be affected to a minor extent by the design of cigarette, the three routinely monitored smoke components provide an adequate guide to the yields of the other analytes examined, across the range of manufactured cigarettes available in the UK in the 1980s.

A further study of air pollution in diesel bus garages.

The concentrations of smoke, polycyclic aromatic hydrocarbons (PAHs), and some gaseous air pollutants have been measured in two London Transport diesel bus garages and compared with observations made in the same garages over 20 years earlier. The main feature of the results was a large reduction in the background concentrations of smoke and polycyclic aromatic hydrocarbons from sources such as coal fires, attributable to the implementation of the Clean Air Act. Contributions from the buses to the benzo(a) pyrene content of the air inside the garages were of the same magnitude as before, being small in relation to former coal smoke contributions.

Respiratory function measurements in a cohort of medical students: a ten-year follow-up.

A cohort of medical students first seen in 1962 has now been examined for a third time. The prevalence of symptoms of cough, phlegm, and breathlessness among them has remained low, and smoking habits have been light in comparison with those of the general population. Results of the three successive sets of measurements of lung function indicate that, in general, optimum values were reached in the early 20s, with little further change up to age 29. There was some evidence of reduced ventilatory capacity in subjects with histories of acute chest illnesses.

Trends in urban air pollution in the United Kingdom in relation to lung cancer mortality.

The substantial reduction in air pollution, and particularly in components such as benzo[a]pyrene in urban areas of the United Kingdom during the past few decades has presented an opportunity to consider further the possible role of carcinogens in the air in relation to lung cancer. While the overall trends in lung cancer mortality have undoubtedly been dominated by changes in smoking, the marked contrasts that at one time existed between these death rates in urban and rural areas have gradually diminished. This may indicate that air pollution contributed appreciably to the urban/rural differences in lung cancer at one time, but it is still difficult to disentangle any effects it may have had from those of changing smoking habits.

Coal fires, industrial emissions and motor vehicles as sources of environmental carcinogens.

One of the most widely studied carcinogenic agents in the environment is the polycyclic hydrocarbon, benzo(a) pyrene. As a component of soot from the inefficient combustion of coal, its association with cancer can be traced back 200 years, but its possible relevance to lung cancer as a widely distributed air relevance to lung cancer as a widely distributed air pollutant has been investigated only during the past 25 years. Domestic coal fires have been shown to be important sources, and smaller amounts come from industrial sources and from motor vehicles. There is evidence now that the concentration of benzo (a) pyrene in large towns in Britain has decreased by a factor of about ten during the last few decades, as a result of changing heating methods and smoke control. In view of the overwhelming effect of cigarette smoking, it is difficult to determine whether the benzo(a)pyrene content of the air has had any importnat effect on the development of lung cancer, but careful analysis of trends in mortality may now throw some light on this. Among other materials with carcinogenic properties that may be dispersed into the general air, asbestos is the one that has been investigated most thoroughly. The association between exposure to asbestos and the development of lung cancer and mesothelioma of the pleura has been clearly demonstrated among people occupationally exposed to the dust, but as far as the general public is concerned, any risk may be limited to the immediate vicinity of major sources. These and other hazards demonstrated among occupational gropus serve as a warning however to maintain careful scutiny of urban air pollutants in relation to the acetiology of cancer.