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How air pollution impacts health

Key learning points:

- Health effects of ambient air pollution can occur as a consequence of short-term spikes in concentrations and long-term exposures

- Individuals susceptible to the adverse effects of poor air quality should be aware of daily pollutant concentrations, by regularly checking the UK Daily Air Quality Index and air pollution alert services

- If people are aware of variations in the health effects of pollutants, there's a greater likelihood of changing behaviour in favour for a healthier population and cleaner environment

Rapid urbanisation means that we are now exposed to a diverse variety of unhealthy concentrations of particles and noxious gases that are continuously released into the atmosphere. These ambient air pollutants are now a significant public health problem, responsible for a growing range of health effects that are well documented from the results of extensive research (incorporating population exposure, observational epidemiology, controlled exposure studies, animal toxicology and in vitro mechanistic work) carried out in many parts of the world.1

People can experience short-term (day to day) exposures to markedly elevated concentrations, when for example pollution is allowed to build up as a consequence of both poor airflow and dispersal. Of greater concern is the long-term or chronic (years to decades) exposure to inherent concentrations of the modern pollutants in today's urban environments. At background levels, these are not indiscernible to the naked eye but they do contribute to chronic health effects and as such, have been coined an 'invisible killer'.

Modern day air pollution

The most abundant pollutants in this mix are as follows: nitrogen dioxide (NO2; generated when oxygen or ozone in the air oxidises nitric oxide, although it is now also emitted directly from exhausts of certain vehicles). Ground level ozone (formed when other pollutants, including NO2 and hydrocarbons, react in sunlight) and a complex mixture of exceptionally small solids or liquids that we term particulate matter (PM). PM10 and the more abundant PM2.5 constitute particles with diameters less than 10 and 2.5 μm. The latter is approximately 30 times less than the width of human hair.

In outdoor air, the major source of NO2 and PM is fossil fuel combustion, primarily from road transport (and particularly diesel vehicles), as well as power stations and factories. The mechanisms underlying the toxic actions of these gaseous and particulate pollutants involve multiple and complex pathways, and have yet to be completely unravelled. However, we do know that the highly orchestrated chain of events is initiated by oxidative stress within the lungs, stemming from increased exposure to oxidants contained within the pollutant and/or a body's decreased antioxidant defence system.2

Health effects of air pollution

It is now fully acknowledged that the ultimate effect of air pollution on public health is to bring about premature death, primarily due to cardiovascular and respiratory diseases.3-5 Each year in the UK, around 29,000 attributable deaths are brought forward because of exposure to ambient PM2.5.6 The recently published report by the Royal College of Physicians (RCP) and Royal College of Paediatrics and Child Health (RCPCH) estimates that this figure increases to around 40,000 if the recently described effects of NO2 are also taken into account.7

Strong scientific consensus also exists that both short and long-term exposures have cardiovascular effects and lead to respiratory disease, with particularly strong evidence for ischaemic heart disease, reduced lung function and heightened severity of symptoms in asthmatics and those with COPD.8,9 The latter is particularly the case during an air pollution episode and as a consequence, such susceptible individuals may call upon increased medication or admission to hospital. It is also worth noting that the chronic health burden of ambient pollution is evident at relatively low concentrations. Additionally, there is no evidence of a safe level of exposure or a threshold below which no adverse health effects occur. In fact, health effects can occur at levels at or below the current World Health Organization Air Quality Guidelines.10,11 Correspondingly, consistent evidence suggests that a reduction in population exposure following a sustained intervention brings about appreciable improvements in public health, including increase in life expectancy12 and better respiratory health.13

More recent evidence has now linked long-term exposure to PM2.5 to atherosclerosis14 and a host of childhood respiratory conditions, including an increased susceptibility to infection,15 symptoms of asthma,16 and low lung function.17 Other than the detrimental effects on cardiopulmonary health, particles from diesel exhaust vehicles are now classified as carcinogenic,18 and an increasing number of studies are investigating the potential for air pollution to negatively influence birth outcomes,19 diabetes,20 neurodevelopment21 and cognitive function.22

Susceptibility

The health response to increases in outdoor air pollution, and particularly to short-term episodes, will vary between subgroups of the population. Individual susceptibility may affect the concentration at which health effects are noticed and/or the rate of increase in symptoms as pollutant levels rise.

Individuals may be more susceptible owing to a genetic predisposition, a chronic cardiovascular/respiratory condition, a metabolic disease (eg diabetes) or a suboptimal level of antioxidants in the diet. Age is also likely to affect response. While the elderly are invariably faced with accumulating chronic conditions and ageing body systems, gestation, infancy and early childhood are vulnerable times as a consequence of developing lung and immune systems. Other contributory factors include physical activity and with that, increased ventilation of the lungs, as well as social deprivation, which frequently goes hand in hand with greater exposure and higher levels of chronic disease.23

Health advice and actions to reduce exposure

The healthy general population is unlikely to experience any short-term health effects from poor air quality unless air pollution reaches very high levels, at which point they may suffer some discomfort such as sore eyes, tickly cough or sore/dry throat. In contrast, it is possible that very sensitive individuals may experience health effects on low pollution days. Athletes, for example, may notice a drop in performance and that deep breathing causes some discomfort in the chest. For adults and children with lung or heart conditions, there is a greater risk of a worsening of symptoms and need for treatment, albeit for the minority. Asthmatics may find that they need to use their inhaled reliever medication on days when levels of air pollution are higher than average. However, individuals with heart and circulatory conditions should only modify their treatment schedule on a health practitioner's advice. Primary care nurses should ensure that patients who fall into the susceptible and sensitive sub-groups (pregnant women, children and the elderly and those with cardiorespiratory conditions) are made aware of: (a) the possible health effects that may be experienced in the event of poor air quality and (b) as outlined below, the different ways they can check daily pollutant concentrations.

In the UK, output from our air quality monitoring network on measured concentrations of different ambient pollutants and air quality modelling systems are processed in different ways. This is through meteorological data and scientific evidence emerging from toxicological and epidemiological research to create a national daily air quality index (DAQI).24,25 In addition to the index itself, accompanying information provides health advice, of which primary care nurses should be conversant, to reduce the impact for the general population and for susceptible individuals.25 In this way, the DAQI, communicated via television, radio, newspapers and internet, can be used to understand air pollution levels and find out about recommended actions and health advice. The ultimate aim is to prevent the adverse effects from short-term elevations in air pollution. By familiarising themselves with the above, nurses in the community can become instrumental in this regard. Other information tools that are becoming increasingly informative and engaging are air pollution alert services that provide real-time data. They proactively alert registered users of impending pollution events via a computer/tablet (websites, email, social media) or phone (texts, apps).26-27

Conclusion

In an ideal world, susceptible individuals should be aware of their air quality by regularly checking the DAQI or targeted notifications for real-time data before setting off to work, school or to pursue leisure activities. This will enable them to take action in the event of increased pollution. Primary care nurses should encourage such practice and in doing so, help vulnerable patients to protect themselves from the effects of air pollution. Interventions to promote a durable change in the attitude and behaviour of the public at large relies on continued education, and optimal communication about the complex relationship between air quality and ill health. The recently published report by the RCP and RCPCH makes excellent reading in acknowledging the impact of air pollution exposure across the course of a lifetime and explaining this in a concise and easy-to-follow format. If people, healthy or otherwise, are aware of variations in the quality of the air that they breathe, the health effects of pollutants as well as concentrations likely to cause adverse effects and actions to reduce pollution (eg, walking/cycling or public transport rather than driving; use of petrol rather than diesel cars in urban areas), there follows a greater likelihood of changing behaviour in favour of not only a healthier population but also a cleaner environment.

References

1. World Health Organization. Review of evidence on health aspects of air pollution. euro.who.int/__data/assets/pdf_file/0004/193108/REVIHAAP-Final-technical-report-final-version.pdf?ua=1. (accessed 4 February 2016).

2. Miller M. The role of oxidative stress in the cardiovascular actions of particulate air pollution. Biochemical Society Transactions 2014;42:1006-1011.

3. Lepeule J, Laden F, Dockery D, Schwartz J. Chronic exposure to fine particles and mortality: An extended follow-up of the Harvard Six Cities study from 1974 to 2009. Environmental Health Perspectives 2012;120:965-970.

4. Faustini A, Rapp R, Forastiere F. Nitrogen dioxide and mortality: review and meta-analysis of long-term studies. European Respiratory Journal 2014;44:744-753

5. Turner M, Jerrett M, Pope C, Krewski D, Gapstur S, Diver W et al. Long-Term Ozone Exposure and Mortality in a Large Prospective Study. American Journal of Respiratory and Critical Care Medicine, 2015. 

6. Committee on the Medical Effects of Air Pollutants. The mortality effects of long-term exposure to particulate air pollution in the United Kingdom. gov.uk/government/uploads/system/ uploads/attachment_data/file/304641/COMEAP_mortality_ effects_of_long_term_exposure.pdf. (accessed 28 February 2016).

7. Royal College of Physicians and Royal College of Paediatrics and Child Health. Every breath we take: the lifelong impact of air pollution. rcplondon.ac.uk/projects/outputs/every-breath-we-take-lifelong-impact-air-pollution. (accessed 28 February 2016).

8. Brook R, Rajagopalan S, Pope C, Brook J, Bhatnagar A, Diez-Roux A et al. Particulate matter air pollution and cardiovascular disease. An update to the Scientific Statement from the American Heart Association. Circulation 2010;121:2331-2378.

9. Kelly F, Fussell J. Air pollution and airway disease. Clinical & Experimental Allergy 2011;41:1059-1071.

10. Crouse D, Peters P, van Donkelaar A, Goldberg M, Villeneuve P, Brion O et al. Risk of nonaccidental and cardiovascular mortality in relation to long-term exposure to low concentrations of fine particulate matter: a Canadian national-level cohort study. Environmental Health Perspectives 2012;120:708-714.

11. Cesaroni G, Badaloni C, Gariazzo C, Stafoggia M, Sozzi R, Davoli M et al. Long-term exposure to urban air pollution and mortality in a cohort of more than a million adults in Rome. Environmental Health Perspectives 2013;121(3):324-331.

12. Pope C, Ezzati M, Dockery D. Fine- particulate air pollution and life expectancy in the United States. The New England Journal of Medicine 2009;360:376-386.

13. Bayer-Oglesby L, Grize L, Gassner M, Takken-Sahli K, Sennhauser F, Neu U et al. Decline of ambient air pollution levels and improved respiratory health in Swiss children. Environmental Health Perspectives 2009;113:1632-1637.

14. Kunzli N, Jerrett M, Garcia-Esteban R, Basagana X, Beckermann B, Gilliland F.et al. Ambient air pollution and the progression of atherosclerosis in adults. PLoS ONE 2010;5:e9096.

15. Macintyre E, Gehring U, Molter A, Fuertes E, Klümper C, Krämer U et al. Air pollution and respiratory infections during early childhood: An analysis of 10 European birth cohorts within the escape project. Environmental Health Perspectives 2013;122:107-113.

16. Gehring U, Wijga A, Brauer M, Fischer P, de Jongste J, Kerkhof M et al. Traffic-related air pollution and the development of asthma and allergies during the first 8 years of life. American Journal of Respiratory and Critical Care Medicine 2010;181:596-603.

17. Latzin P, Roosli M, Huss A, Kuehni C, Frey U. Air pollution during pregnancy and lung function in newborns: A birth cohort study. European Respiratory Journal 2009;33:594-603.

18. International Agency for Cancer Research. Diesel engine exhaust carcinogenic. iarc.fr/en/media-centre/pr/2012/pdfs/pr213_E.pdf (accessed 4 February 2016).

19. Sapkota A, Chelikowsky A, Nachman K, Cohen A, Ritz B et al. Exposure to particulate matter and adverse birth outcomes: A comprehensive review and meta-analysis. Air Quality, Atmosphere and Health 2012;5:369-381.

20. Raaschou-Nielsen O, Sorensen M, Ketzel M, Hertel  O, Loft S. Tjonneland A et al. Long-term exposure to traffic-related air pollution and diabetes-associated mortality: A cohort study. Diabetologia 2013;56:36-46.

21. Guxens M, Sunyer J. A review of epidemiological studies on neuropsychological effects of air pollution. Swiss Medical Weekly 2012;14:w13322.

22. Ranft U, Schikowski T, Sugiri D, Krutmann J, Kramer U. Long-term exposure to traffic-related partic- ulate matter impairs cognitive function in the elderly. Environmental Research 2009;109:1004-1011.

23. Bell M. Zanobetti A. Dominici F. Evidence on Vulnerability and Susceptibility to Health Risks Associated With Short-Term Exposure to Particulate Matter: A Systematic Review and Meta-Analysis. American Journal of Epidemiology 2013;178:865-876.

24. Kelly F, Fuller G, Walton H, Fussell J. Monitoring air pollution: Use of early warning systems for public health. Respirology 2012;17:7-19

25. Department for Food, Environment and Rural Affairs (DEFRA). About air pollution. uk-air.defra.gov.uk/air-pollution/ (accessed 4 February 2016).

26. London Air Quality Network (LAQN). London air applications. londonair.org.uk/LondonAir/MobileApps/ (accessed 4 February 2016).

27. CityAir. CityAir Forecast. cityairapp.com/ (accessed 4 February 2016).