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1. The report "Transport and Health in London" has attracted significant attention from the media and has been held to show that concern about the possible effects on health of transport-generated air pollution in London may have been exaggerated. The review was one of a number of reviews commissioned to inform the London Regional Office of the NHS Executive's "Health Strategy for London". The topic the authors of the report have addressed is an important one and we accept the need for a careful study to put the effects on health of air pollutants in perspective with other factors. The balance of advantages and disadvantages of various transport policies is difficult to strike and a broad examination of the implications for health of different policies is needed.

2. In preparing their report the authors have drawn extensively from our reports on the effects of air pollutants on health. ^{[1], [2]} In doing so the authors have chosen passages to support their thesis with little regard for the context of our remarks or for our broader conclusions. For these reasons we feel we should make our position clear.

3. There is sufficient published evidence to show that daily fluctuations in exposure to current levels of air pollution in London are associated with short-term variations in ill-health. [^{3 - 7]} We made clear in our report " Quantification of the Effects of Air Pollution on Health in the United Kingdom" (QUARK) that deaths occurred earlier and that hospital admissions for respiratory diseases were probably both caused de novo and advanced by exposure to air pollutants. Evidence regarding the effects of particles, sulphur dioxide and ozone was sufficiently developed to allow us to start to quantify these effects. For nitrogen dioxide and carbon monoxide there is insufficient evidence to allow quantification of effects as yet but there is evidence to suggest that exposure to current levels of these pollutants affects health. We wish to make clear that we have not discounted the effects of nitrogen dioxide and carbon monoxide on health. Our understanding of likely effects at a range of ambient concentrations is embedded in our advice to DETR on their banding system for describing levels of air pollutants. This advice is available on the DETR website. [^8]

4. As regards the known carcinogens benzene, 1,3-butadiene and some polycyclic aromatic hydrocarbon compounds we accept the view expressed by the Expert Panel on Air Quality Standards (EPAQS):

"The risk associated with current ambient levels is likely to be exceedingly small". [^{9], [10]}

Having said that, we wish to stress, as was stressed by EPAQS, that these compounds are genotoxic carcinogens and no absolutely safe level of exposure can be identified. There is no case for complacency and further reductions in concentrations are desirable.

5. Evidence of possible adverse effects of long-term exposure to air pollutants is accumulating. As we pointed out in the QUARK report, these could be more important than the effects of short-term increases in concentrations of pollutants. Work to clarify the impact of long-term exposure to air pollutants is proceeding but to date, is insufficient to allow us to be certain of the size of this effect. The results of preliminary work, however, are certainly consistent with current levels of pollution having a significant effect on life expectancy. The potential importance of these long-term hazards did not come across significantly strongly in the report by Glaister et al and is very important.

6. We are concerned that the authors of the report sought to compare current levels of air pollution in London with those found in other "mega cities" around the world. These cities included many in the third world, many of which have very significant air pollution problems caused by a range of local factors. The authors did not compare London with other European cities which would have been more relevant. In addition, the report did not mention that legally binding Limit Values have recently been agreed within the EU for a number of air pollutants. Reduction in traffic pollutant emissions may be needed in London to achieve these.

7. Over the years great advances have been made in controlling the source of many levels of air pollutants in London. Modern techniques of investigation have, however, shown that health is still affected by air pollution and we strongly support the Air Quality Strategy for England, Scotland, Wales and Northern Ireland in its aim to reduce further these effects. We also note that the UK signed the World Health Organization's Charter on Transport, Environment and Health in June 1999 on behalf of all WHO Europe Member States (details can be found at the website: http://www.who.dk/London99/transport02e.htm).

References

1. Department of Health. Committee on the Medical Effects of Air Pollutants. Quantification of the Effects of Air Pollution on Health in the United Kingdom. London: The Stationery Office, 1998.

2. Department of Health. Committee on the Medical Effects of Air Pollutants. Non-Biological Particles and Health. London: HMSO, 1995.

3. Anderson HR, Ponce de Leon A, Bland JM, Bower JS, Emberlin J, Strachan DP. Air pollution, pollens and daily admissions for asthma in London 1987-92. Thorax 1998; 53:842-848.

4. Anderson HR, Ponce de Leon A, Bland JM, Bower JS, Strachan DP. Air pollution and daily mortality in London: 1987-92. Br Med J 1996; 312:665-669.

5. Atkinson RW, Anderson HR, Strachan DP, Bland JM, Bremner SA, Ponce de Leon A. Short-term associations between outdoor air pollution and visits to accidents and emergency departments in London for respiratory complaints. Eur Respir J 1999; 13:257-265.

6. Bremner SA, Anderson HR, Atkinson RW, McMichael AJ, Strachan DP, Bland JM, Bower JS. Short term associations between outdoor air pollution and mortality in London 1992-4. Occup Environ Med 1999; 56:237-244.

7. Atkinson RW, Bremner SA, Anderson HR, Strachan DP, Bland JM, Ponce de Leon A. Short-term associations between emergency hospital admissions for respiratory and cardiovascular disease and outdoor air pollution in London. Arch Environ Health 1999; 54:398-411.

8. Department of the Environment, Transport and the Regions. Air Pollution - What it Means for Your Health. London: DETR, 1998. Also available on DETR Website: http://www.environment.detr.gov.uk/airq/aqinfo.htm.

9. Department of the Environment. Expert Panel on Air Quality Standards. Benzene. London: HMSO, 1994.

10. Department of the Environment. Expert Panel on Air Quality Standards. 1,3-Butadiene. London: HMSO, 1994.

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