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Australian research is needed to refine recently set Australian standards for air pollution
MJA 1998; 169: 452-453
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There is now a mounting body of evidence that fine airborne particles have significant adverse health effects. In this issue of the Journal, Lewis and colleagues report the results of a cross-sectional study of school children conducted as part of the Hunter Illawarra Study of Airways and Air Pollution (HISAAP).1 In brief, the HISAAP investigators found that, in children, outdoor PM10 (particles with an aerodynamic diameter less than 10 µm) concentrations are associated with chest colds and night time cough, but not with wheezing. An important point is that these associations were found at relatively low particulate concentrations -- the most polluted area had an annual average PM10 of 43.7 µg/m3. A good response rate was achieved and appropriate multivariate statistical analysis was conducted to control for confounders such as indoor environmental and individual factors. These results are consistent with previous time series, cross-sectional and cohort studies of the effects of air pollution on both children and adults, predominantly conducted in Europe and North America. The Box contains a summary of the overall health effects found in these studies. Although many of the criteria for causation have now been satisfied (such as a dose-response relationship, consistency of association, and correct sequence of exposure and effect), the lack of data from controlled clinical trials or relevant animal experiments means that the underlying biological mechanisms are not yet understood.
Epidemiological studies consistently find associations between exposure to airborne particles and short-term human health effects, and there is no threshold concentration below which these associations disappear. These facts have spurred some regulatory agencies to action. In July 1997, the United States Environment Protection Agency (EPA) set 24-hourly average concentration limits of 65 µg/m3 and an average annual limit of 15 µg/m3 for PM2.5 (particles less than 2.5 µm diameter). These complement the 1987 limits for PM10 of 150 µg/m3 for a 24-hour average and 50 µg/m3 for an annual average. There is some evidence that fine particles (PM2.5) may be even more relevant to public health than PM10.3 In Australia, the development of airborne particle standards to protect public health has proceeded more slowly. In 1990, Streeton first proposed PM10 objectives of 120 µg/m3 for a 24-hour average and 40 µg/m3 for an annual average not to be exceeded for "acceptable" air quality.4 Shortly afterwards, one of us (MJA) expressed the hope that "politicians and bureaucrats would not shirk the task" of introducing the necessary legislation and regulations.5 On 26 June 1998, the National Environment Protection Council finalised the National Environment Protection Measure (NEPM) for Ambient Air Quality.6 This has at last set an air quality standard of 50 µg/m3 for a 24-hour average for PM10. However, because Australian cities are subject to bushfire smoke, the NEPM still permits five allowable exceedance days per year. Closer examination of the evidence summarised in the Box reveals some inconsistencies. It is difficult to envisage a mechanism which results in less exacerbation of mild effects such as cough (1.2% increase per 10 µg/m3) than of respiratory mortality (3.4% increase per 10 µg/m3). Issues such as these have led to continuing controversy over the role of particles in short term health effects.7,8 This was acknowledged in Australia when the National Environment Protection Council agreed, in response to input during the consultation process, that the NEPM and the standards within it will need review within 10 years. There was also agreement that the particle standard needed review, especially the need for a PM2.5 standard. Such a review should be commenced by 2001. Furthermore, a review of the whole NEPM and all six criteria pollutants (airborne particles, sulfur dioxide, ozone, oxides of nitrogen, carbon monoxide, and lead) should be started by 2005. The US National Research Council recently recommended that the US EPA develop a long term (14-year) research program to examine particulate matter.9 Their top 10 priorities are to:
Australia needs to conduct similar research because the air quality, the population's exposure to it, and the resulting health effects will differ from those in other countries. The composition, size distribution, and other characteristics of particles differ from those in the United States, as does the mix of background air pollutants in which the particles are suspended, and the susceptibility of the population exposed to such particles. For example, the prevalence of asthma and other allergic disorders is significantly higher in Australia than in either the United States or Europe.10 The results from studies such as HISAAP allow Australian researchers to contribute to this process of examining, in greater detail, the relations between particles and health. It is to be hoped that during the time-frame for revision of the NEPM for ambient air quality, the necessary environmental, epidemiological and toxicological research will be supported to resolve some of the uncertainties. Indeed, although not without considerable economic pain, the forthcoming closure of the steel mills offers a unique opportunity to determine whether improved air quality will actually result in any improved health outcomes for Newcastle residents. Only when such evidence is available can we be confident of setting airborne particle standards that will adequately protect the health of the Australian population. Michael J Abramson Tom Beer
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