Health effects of exposures to mixtures of air pollutants / Advisory Group on the Medical Aspect of Air Pollution Episodes.

  • Great Britain. Advisory Group on the Medical Aspects of Air Pollution Episodes.
Date:
1995
Catalogue details

Licence: Open Government Licence

Credit: Health effects of exposures to mixtures of air pollutants / Advisory Group on the Medical Aspect of Air Pollution Episodes. Source: Wellcome Collection.

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    Effects on public health of exposures to combinations of air pollutants acid or water fogs protected against the effects of ozone exposure. 8.17 In combination studies involving several pollutant gases there is no evidence that the combination produces a greater effect than would be expected from summation of the responses to individual gases. When a response has been seen the dominant effect has usually been due to ozone. 8.18 The number of studies in which subjects have been exposed to ambient polluted air in a chamber is limited. The data suggest that, in Los Angeles at least, ozone is the major contributor to a reduction in lung function caused by ambient air. 8.19 Very few studies have attempted to look at the interaction of gases with particles. Because of the diverse nature of particulate material it would be extremely difficult to do this in a systematic manner. 8.20 Interactions between air pollutants may have been underestimated in chamber studies due to the small size of many studies, limited duration of exposure and the confounding effects of prior exposure to ambient pollutants. 8.21 The epidemiology of the health effects of mixtures of air pollutants is poorly developed. Pollutants tend to be analysed separately and some pollutants are rarely measured or are poorly characterised (especially particles). Thus, there is an incomplete picture of the pattern of exposure in reported studies of health effects. There are also problems in ascertaining the actual exposure of the population under study, and the dose received by the lung. 8.22 Even where the pattern of exposure is reasonably well described, analyses have tended to be in terms of individual pollutants rather than of mixtures; so far, little progress has been made in developing indices of mixed pollution exposure. 8.23 Since studies from the United Kingdom are still limited it has been necessary to extrapolate from studies elsewhere. Most confidence has been placed on recent studies where the emission sources and weather conditions are reasonably similar to those in the United Kingdom, i.e. studies from Europe in particular. If all air pollutants produced similar types of public health effects, as has been suggested for particles of differing composition, extrapolation would be possible to a greater extent. In general this is not unreasonable since the lung has a limited range of responses to particles and toxic gases; however, differences do occur, especially as regards the airway response to ozone and sulphur dioxide. 8.24 Three types of research design are available for examining short term effects but all have methodological weaknesses which must be considered when examining the evidence for a statistical association and causal relationship. 8.25 Episode studies are essentially one-event analyses of major air pollution episodes. They are subject to low statistical power, confounding (e.g. by temperature) and coincidental influences (e.g. concurrent respiratory epidemics). Nevertheless, the design of episode studies is easy to understand and their results are directly relevant to policy concerning standards and medical advice during episodes. 8.26 The evidence from episode studies that air pollution episodes in the United Kingdom may cause adverse health effects is reasonably convincing. Studies from the United Kingdom and Europe indicate that adverse health effects may occur in the winter pollution conditions which can arise in the United Kingdom. When health effects occur during such episodes, they usually involve subjects (mainly older persons) with advanced cardiorespiratory disease. There are no published studies of the effects of single summer ozone episodes in the United Kingdom, but unpublished data indicate that hospital admissions and mortality increased during the 1976 episode. While consistent with an effect of ozone, high temperatures could also have been responsible. 11]