The evidence base specifically on pollution inequality has been developed through analysis of pre-existing spatially disaggregated environmental data against social variables, predominantly using various measures of poverty, deprivation and socioeconomic status.
The most robust evidence relates to air quality. Concentrations of nitrogen oxides (NOx) and fine particulates (PM10) display a strong social gradient. For mean annual concentration, a U-shaped distribution (Figure 6.2a) has been repeatedly found across various studies, as lowest concentrations tend to be in more rural areas of medium deprivation.7,8,19,24
Considering only locations where concentration values exceed the national air quality standard annual average limit values, the U shaped distribution disappears, and a very strong gradient is evident (Figure 6.2b). In 2001, of the 2.5 million people resident in areas where the annual mean NO2 limit value was exceeded, over half were in the poorest 20% of the population; by 2011 the exceedance population had fallen to 0.6 million due to overall improvements in air quality, but 85% of this
population was in the poorest fifth25 (Figure 6.3). Studies elsewhere in Europe have varied in geographic extent, spatial unit, social metric, atmospheric pollutant, and analytical method, yet broadly confirm that the most deprived populations experience higher and more health-threatening environmental exposures.26,27
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Figure 6.2a Social distribution of annual average NO2 concentration in
i Bars denote 5-95 percentile range, N=8,414.
ii Each decile represents the average of electoral ward mean NO2, measured as an annual mean.
Source Walker G et al.Environmental Quality and Social Deprivation. Phase II: National Analysis of Flood Hazard, IPC Industries and Air Quality. The Environment Agency (2003) 0 5 10 15 20 25 30 35 40 45 1 2 3 4 5 6 7 8 9 10 Deprivation decile M e a n w a rd m e a n N O2 c o n c e n tr a ti o n (u g /m 3 )
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Figure 6.2b Population resident in areas exceeding the annual average
legal limit value for NO2, by deprivation decile, England
i Annual mean standard is 40 ug/m3, applied as a ward average. ii Decile 1 is most deprived. All deciles have 4.9 million people.
iii 2.51 million people are in an NO2 exceedance ward, 5.1% of the population of England.
iv 53% of all person exceedances are in the most deprived quantile.
Source Walker G et al.Environmental Quality and Social Deprivation. Phase II: National Analysis of Flood Hazard, IPC Industries and Air Quality. The Environment Agency (2003) 0 100 200 300 400 500 600 700 800 900 1 2 3 4 5 6 7 8 9 10 Deprivation Decile P o p u la ti o n ( th o u sa n d s) i n N O2 e x c e e d e n c e w a rd
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Figure 6.3 Great Britain population in lower super output areas (LSOAs) where NO2 exceeds the 40 µg m3 annual
average legal limit value
Q1 is the least deprived fifth, Q5 the most deprived fifth. Concentration values are the mean of annual average concentrations for LSOAs where NO2 concentration >40 µg m3. NB. log-scale (25)
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Ethnic minority populations in the UK are also exposed to higher concentrations of NO2 and PM10 but there is no indication whether this is a casual link with ethnicity or a facet of the socioeconomic status of ethnic minority groups; nor is there consensus on the link between ethnic susceptibility to air pollution and health.28,29 However, fetuses, babies and children are known to be more susceptible to poor air quality30 and increased exposure of children in UK national small area analyses has been observed for NO27,29 but not fine particulates.29 Gender has been little studied with respect to the social distribution of pollution31, but can be expected to become more prominent as environmental inequality analyses begin to consider an individualistic perspective better able to account for temporal variability in exposure, for example due to differences in daily travel patterns.6
Indoor air quality has been less studied, but research in the US shows a positive association between deprivation and poor indoor air quality (NO2, fine particulates, VOCs, lead, allergens). Indoor air quality is determined by outdoor air quality, indoor pollutant sources and occupant activity, and physical features of housing.32 No comparable equity research exists for the UK, but it is reasonable to assume a similar association, given the strong association of deprivation with outdoor air pollution, and smaller, often lower quality housing.
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Other pollutants and risks
For other environmental pollutants and risks (Table 6.1) evidence exists of a strong association (for England) between deprivation and proximity to activities regulated under Industrial Pollution Prevention and Control (IPPC) legislation, including major industrial and petrochemical sites and waste incinerators.33 Site specific studies are equivocal in terms of associated health impacts, whilst at a national level health impacts are analysed within the wider context of air quality (see below), for which road traffic is the dominant source. Landfill sites are geographically associated with deprivation18,34, although study results are dependent on methodological choices35 and not clearly associated with elevated health risk.36 In England, exposure to brownfield land is higher in the north and is associated with spatial inequalities in mortality and morbidity both within English regions, and between them, although differential brownfield exposure does not appear to contribute to the north-south health divide, probably due to differences in the distribution of types of brownfield land.37
An analysis of ambient noise emission levels from road and rail traffic in Birmingham found a weak relationship with deprivation38 but no other UK noise studies exist. A systematic international review of noise health effects, focused on vulnerable groups, concluded that differentials in both physiological and psychological effects were largely anecdotal, with subgroup-specific exposure-effect studies needed.39 There are various newer forms of health threats from pollution (see Chapter 4 of this report, ‘New horizons’) where questions of inequality are yet to be examined.
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Multiple environmental hazards
Environmental inequalities research has also sought to understand the social distribution of environmental metrics in combination. National and region-specific analyses show that with increasing area deprivation there is a greater likelihood of populations being exposed to multiple environmental hazards, in terms of both the intensity of a specific hazard (such as the clustering of industrial or waste facilities), and local exposure to a multiplicity of hazard types (such as the coincidence of industrial hazards, poor air quality and flood risk).19,40-42
Environmental inequalities over time
Tracing how environmental inequalities develop over time is an important step in understanding how they have arisen, but such studies tend to be constrained by a lack of small area longitudinal data. However, an analysis of air quality change in Britain from 2001-2011 reveals a social gradient in environmental change.25 Where air quality has improved (falling NO2) it does so most quickly in the least deprived areas, and where it has worsened (rising PM10) it does so more quickly in the most deprived areas. This may be a consequence of the more polluted initial conditions experienced by the more deprived communities (for example greater air quality improvement is needed to attain ‘good’ air quality than in the less polluted, more affluent areas). Overall improvements in air quality should have reduced the associated national disease burden, but the social gradient (Figure 6.3) implies social inequality in how this benefit is distributed.25 This suggests that interventions that reduce pollution overall can deliver health gains, but if intended to reduce health inequalities, they require more targeted interventions (discussed further below).
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