Non-biological particles and health / Committee on the Medical Effects of Air Pollutants ; chairman, Stephen Holgate ; chairman of the Sub-Group on Non-Biological Particles and Health, Robert Waller.

Great Britain. Committee on the Medical Effects of Air Pollutants

Date:: 1995

Credit: Non-biological particles and health / Committee on the Medical Effects of Air Pollutants ; chairman, Stephen Holgate ; chairman of the Sub-Group on Non-Biological Particles and Health, Robert Waller. Source: Wellcome Collection.

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$Chronic effects into the more stable accumulation mode, and they would represent only a small proportion of the mass of material measured as PM,,, though they would represent a high proportion of the number of particles present. Although reported studies indicate a range of effects, from small changes in ventilatory function or exacerbations of asthma through to increases in deaths among the elderly or chronic sick, it does not necessarily follow that the same components would be involved in each effect. Implications for public health in the UK 10.23 Weconclude that, in terms of protecting public health, it would be imprudent not to regard the associations as causal. We also believe that the findings of the epidemiological studies of the acute effects of particles, which have been conducted in the US and elsewhere, can be transferred to the UK at least in a qualitative sense. However, we consider that there are insufficient UK data available to allow direct extrapolation and reliable estimation of effects in the UK. 10.24 It would be possible, for any health effect of interest, to take a weighted average of the results of well-conducted published studies and apply this to conditions in the UK. [This would usually imply conversion across different measures of particles.] Thus, the relative risk calculated by Schwartz! with regard to effects of particles on mortality was 1.06 (CI: 1.05-1.07) for a 100 ug/m* change in total suspended particles, equivalent to some shortening of life in approximately 1% of daily deaths per 10 wg/m? increase in PM,,. Application to the UK of the results even of such structured meta-analyses does not formally take account of uncertainties in extrapolating to different air pollution mixtures (with generally lower concentrations of suspended particles), climate patterns and at-risk populations. Because of these uncertainties, we think it would be unwise to offer a single coefficient with regard to effects on mortality or any other index of ill health. The reader is referred to the tables in Annex 8A to Chapter 8, with the warning that the estimates based on studies reported in these tables are likely to provide only a first approximation to the actual effect. Studies should be undertaken urgently to allow better quantitative predictions to be made. Measurement 10.25 Unless, or until, a clearer idea is obtained of the sizes or other characteristics of SPM that are most relevant to effects on health, we consider it appropriate to measure SPM in terms of PM,,, covering the whole range of material capable of being inhaled and reaching the deeper parts of the respiratory tract. However, there is also a pressing need for investigation of the particle size distribution, of subfractions such as PM, , and for considering surface area and number concentrations as well as mass. Averaging times 10.26 The epidemiological studies of acute effects have been related to PM,, values assessed over 24 hour periods, or sometimes over several days. It may be that number and mass concentration over shorter periods of time are important, but this aspect has not been investigated and it should be followed up. The hourly means available from continuous monitoring instruments do, however, help to characterise the pollution exposures. It has been suggested that the role of rate of change of concentrations of particles and other pollutants may also be important though this is seldom taken into account in monitoring strategies. 10.27 Evidence regarding the effects of long term exposure to particles on health is less well developed than that regarding the acute effects. The possibility of confounding in such studies is considerable and it is difficult to estimate the exposures of individuals over relevant time periods. Here again the results of recent US studies are probably transferable to the UK in a qualitative sense though confidence in the accuracy of the predictions is lower than with regard to the acute effects of particles. 10.28 Though the evidence is limited we advise that it would be prudent to consider these associations as causal.$