When it's not good to take the air

An estimated 8,100 people die prematurely each year in the United Kingdom as a result of exposure to particulate matter, according to a 1998 report of the UK Committee on the Medical Effects of Air Pollutants. A more recent report of the same committee suggests that millions of life years could be gained if particle levels were cut. Particulate Matter: Properties and Effects upon Health emerged from a session on particulate aerosol at the scientific meeting Micro '98. The topic unites the different disciplines and strands of activity in the Royal Microscopical Society, according to Vyvyan Howard, former president of the society and co-editor of the book, and this has led to a strong UK focus.

In the introduction, Robert Maynard gives a historic overview of particulate matter research. Air pollution is not a new phenomenon. The history of complaints about smoke in the UK can be traced back to the 13th century, when the use of coal for domestic heating and the firing of furnaces produced severe air pollution in London. Though there have probably been significant fluctuations in the degree of pollution, the problem of particles has persisted in London for 700 years, Maynard says. It is difficult to say when pollution in London was at its worst, but in 1952 the Great Smog caused 4,000 extra deaths. This was the last straw for many people. Legislation was introduced to reduce pollution, and it triggered research into the effects of air pollutants on health. Air-pollution levels fell rapidly and health effects were thought to decrease equally, even to a non-existent level.

This perception changed dramatically in the late 1980s and early 1990s when epidemiological studies provided evidence that day-to-day variations in the already low concentrations of particles and other pollutants were still associated with effects on health, resulting in thousands of premature deaths each year in the UK alone. New research programmes were begun in the UK, and Maynard played an instrumental role.

Maynard's introduction is followed by Anthony Seaton's chapter on the many health effects of airborne particles, including occupational exposure and smoking, both of which are largely ignored in the rest of the book. This is unfortunate because various occupational lung diseases, including occupational asthma and cancer resulting from exposure to biological, mineral and other particles in the workplace, still affect a considerable number of people.

Three chapters deal with physico-chemical and morphological characterisation of airborne particulate matter and with structural and physical chemistry of nano-particles. A variety of analytical techniques that are used to determine the physico-chemical characteristics of particles are discussed - including transmission electron microscopy, scanning electron microscopy, field emission scanning electron microscopy, and electron probe X-ray microanalysis - and they produce some fascinating pictures. Airborne particulate matter in urban environments is complex and dynamic. There is considerable variation in composition, shapes and sizes depending on source and environmental conditions.

The following three chapters deal with the lung deposition of diesel particulates, the biological effects on lung epithelium of particles and the toxicology of ultrafine particles. John McAughey estimates that the average adult inhales about 5.4 x 1011 number of particles a day. The focus of health research over the years has shifted to understanding the mechanism of damage and repair and to smaller particles; from PM10 (particulate matter with a diameter of less than 10mm), to PM2.5 to ultrafine particles (less than 100nm in diameter).

There is still uncertainty about the mechanism of damage, but inflammation and oxidative stress play a significant role. Ken Donaldson, Roy Richards and colleagues give an interesting insight and the evidence of strong effects of ultrafines in toxicological experimental research. A separate chapter on the epidemiology of particles would have fitted in well in this health section.

Roy Harrison reviews the sources and behaviour of atmospheric particulate matter but omits the link to people's personal exposure to particles, essential in health and environment research. In Greater London, traffic accounts for nearly 80 per cent of PM10 emissions. Martin Williams in his informative chapter on air-quality strategies in respect of particles points out that the major problem in marrying policy to the science that informs it is that the timescales never match. Even if there is sufficient science in place and the problem of characterising the scientific essentials of an issue is solved, policy formulation is then determined by other issues such as the social, economic and political aspects of the problem. Overall the book has some interesting and well-written chapters - but also some gaps, and for many chapters familiarity with the topics and techniques is needed.

Mark J. Nieuwenhuijsen is senior lecturer in environmental epidemiology, Imperial College, London.