The need for research into the health effects of ozone and other air pollutants was highlighted by the Committee's report on ozone and health last year (ENDS Report 196, pp 9-10). The Government accepted its proposals for a new system of air pollution warnings, but failed to respond at all to its recommendations for research.
Professor Holgate's comments at a National Society for Clean Air workshop in Oxford in March have put the issue back on the agenda. He believes there is a particular need for studies into the effects of ambient pollution levels on the human airways and into the epidemiological relationship between morbidity and pollution episodes - especially those involving ozone.
Several recent overseas studies have suggested that ozone is implicated in the onset of asthma as well as contributing to the severity of individual attacks. Air pollution problems in the UK are different from those in North America and Japan, where most of the research was conducted. Professor Holgate says that work is now needed to identify the effects of pollutants in the UK and separate them from the many other factors which may influence health.
Hospital admissions for asthma in the UK increased by a factor of four between 1975 and 1985. And a 1990 study of wheezing in primary school children by a team at St Thomas's Hospital found that symptoms were on the increase at a rate of about 5% per year.
Professor Holgate told the Oxford meeting that given the constant genetic stock of the population, the implication was that environmental factors were involved in the increase. He believes that an environmental insult in the first year of life - particularly exposure to ozone - can sensitize an individual to allergens and lead to the development of asthma.
A recent Canadian study showed that asthmatics exposed to 120ppb ozone for one hour at rest were sensitive to allergens at half the concentration of those inhaling air. And Japanese research has shown that new-born animals can be sensitised to allergens by exposure to ozone.
These studies have raised important questions about the longer-term effects of exposure to relatively low ozone concentrations. Holgate believes that ozone may act by attacking the delicate lining of infants' bronchial tubes, weakening the cell walls and allowing allergens to breach the lung's defences.
The highest ozone levels are found in the south and east of the UK. Last year's report by the advisory committee pointed out that this distribution largely coincides with the areas where bronchial asthma is most common - although it cautioned that other factors may explain this pattern. No research is being funded by the Department of Health on this or any other aspect of ozone pollution.