Health and environment

5 Pollution

Air pollution

There are many popular beliefs about air quality and health. As a child you might have been exhorted to, ‘go out and play in the nice fresh air’. Mountain air is often regarded as being particularly beneficial, especially for those who are recuperating from or suffering some types of respiratory diseases.

Q : Over a period of time, the body adjusts to functioning normally at low PO₂ (i.e. the body adapts to high altitude). Describe how these changes to the respiratory and circulatory system would benefit someone with a respiratory disease.

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The lungs’ response to polluted air can lead to the development of chronic bronchitis and ultimately emphysema, which is often now called ‘smoker's lung’. But one of the fastest-growing health problems world-wide is asthma. In the popular press the cause of asthma is often said, incorrectly, to be industrial pollution. There is no scientific evidence for this causal link.

Q : How does the geographical distribution of asthma counter suggestions that it is caused by industrial pollution?

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Q : What factors are believed to trigger asthma attacks?

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Although acute asthma attacks appear to be precipitated by an allergic response to inhaled particles of plant or animal proteins, asthma can, like other respiratory conditions, be exacerbated by industrial air pollution.

Exact relationships between air quality and health are hard to establish, as we have to rely on epidemiological evidence rather than scientific experimentation. There is also a wide range of susceptibility between different individuals and between people of different ages. As you might expect, the very young and the very old are most at risk. There may be an immediate effect but there can also be long-term effects. There were 41000 excess (i.e. additional) deaths attributed to the 1952 London smog (smog is a combination of smoke particles and fog droplets). Of these, 90% were persons aged 45 or older (we are not implying that members of this group are necessarily ‘old’!); amongst infants of 12 months or less the death rate doubled. Some deaths occurred during the smog but others were recorded immediately afterwards. Studies suggested that the high levels of pollutants at that time had lowered the resistance of these individuals to diseases such as influenza, and their resistance remained low for a period although the air quality had improved. The pollutants implicated in this episode were smoke particles and sulphur dioxide (SO₂). Both are emissions from burning fuels; sulphur dioxide is also produced in many industrial processes. Levels of these two pollutants have been monitored in the UK since 1912. Table 4 shows a clear correlation between episodes of high concentrations of these substances in the atmosphere and increased mortality from respiratory disease.

Q : In which season do all these air pollution episodes occur?

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Q : Why do these episodes all occur in winter?

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There are also meteorological reasons for the pollutants remaining at or near ground level rather than being dispersed into the upper atmosphere.

Whilst the need for domestic and commercial heating is highest in winter in cool climates, in warmer cities a different kind of smog is prevalent which has effects on health that are just as severe. This is exemplified by the photochemical smog in cities like San Francisco, USA. Here, the main pollutants are chemicals from traffic emissions (oxides of nitrogen and ozone) trapped close to ground level by local climatic conditions. Regulations to combat polluting emissions from vehicles now exist in economically developed countries (EDCs), such as those of the European Union (EU) and the USA. There are also Clean Air Acts in these countries. However, these acts target the dispersal of industrial pollutants, for example by the use of high chimneys, as much as the reduction of emissions. In the main, it is expensive to reduce emissions and this presents particular problems for economically less developed countries (ELDCs). They wish to reap the benefits of industrialization but cannot afford to use the more expensive techniques that are needed to clean up emissions. Table 5 compares levels of air pollution in EDCs and ELDCs recorded in the mid-1980s. Since then, conditions have generally improved in EDCs but have deteriorated in ELDCs.

Air pollution problems in ELDCs are of concern, not for altruistic reasons, but because air does not acknowledge national borders. Pollutants generated in one country can, in time, affect many other countries. As an illustration, between 27 November and 5 December 1962, there were high levels of air pollution noted in a number of major cities in the north of the USA. Similar conditions hit London on 5 December (Table 4), nine days after they had first been noted in New York; two days later they were reported from Germany, then France, Czechoslovakia and Holland in Europe; later still Osaka in Japan was affected too.

Sulphur dioxide and oxides of nitrogen have direct effects on health, particularly on the health of those people who have respiratory diseases. There is an indirect effect too because they are responsible for the deposition of acid rain that damages many organisms, and this could potentially include humans, through the workings of food webs. The increased acidity of aquatic environments encourages the uptake of toxic ions of the so-called heavy metals – lead, mercury, cadmium, copper and nickel – by the primary consumers.

Q : What are the primary consumers in this ecosystem?

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The result so far seems to have been a depletion of fish stocks as adults are poisoned and eggs fail to develop. No cases of human poisoning following the ingestion of contaminated fish have been reported as a consequence of acid rain, but this remains a possibility. Establishing that acid rain is a global problem and getting international agreements on air quality has taken decades. There is still no scientific agreement on the extent to which acid rain causes certain types of environmental damage, but other concerns, such as the depletion of the ozone layer in the upper atmosphere and global warming, are forcing the international community to collectively examine issues surrounding air pollution. Some of the difficulties can be illustrated in relation to the phenomenon of global warming.