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| Block 8: Environmental Issues and Public Health - Air Pollution Chapter 3: The Main Air Pollutants; Their Health Impacts; Exposure - Response Relationships (Continued) |
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Dioxins and furans are two groups of extremely harmful substances emitted from waste incinerators that are not equipped with the most sophisticated operational and emission control systems. This is one of the main reasons for communities’ opposition to the use of incineration as a means for "disposal" of solid waste. (Other reasons are - incineration discourages recycling and reuse of the "waste" materials, and is wasteful of energy and other natural resources.
Dioxins and furans belong to a group of substances known as Persistent Organic Pollutants (POPs) or Persistent Toxic Substances (PTS). Particulate matter containing heavy metals (principally Pb) or persistent organic compounds (such as dioxins) contaminate soil and crops. Exposure to these types of contaminants occurs mainly through ingestion of contaminated food or soil rather than through inhalation of the polluted air.
Exposure-response relationships, including unit risk factors for cancer-inducing pollutants such as benzene and 1-3 butadiene, are discussed and summarised in references 1 and 2.
The question of the exposure-response relationship for each of the pollutants may be approached from one of two perspectives: a risk based approach or a "toxicological" approach that assumes that there is a threshold below which no adverse effects occur. The vast scientific literature on the relationship between exposure to air pollution and health has been reviewed and summarised in a number of WHO publications, including Air Quality Guidelines (2000) i. Of the pollutants under consideration for the API (SO2, NO2, PM10, PM2.5, O3 and CO), the PM10, PM2.5 and ozone do not do not have an apparent threshold value below which the risk of adverse health effect is zero. Continuing research indicates that SO2 and NO2 may not have threshold values either ii. In other words, except for CO, exposure to these pollutants carries a finite risk of an adverse health effect.
The WHO has also published a technical report proposing a procedure for Health Impact Assessment in the EU iii (WHO HIA report), using Relative Risk factors for SO2, NO2, PM10, PM2.5 and O3 in relation to a range of health endpoints. The data and methodologies in these publications (and the relevant primary sources) are under evaluation for use for the development of the DAPPS APIs.
Table 1 has been adapted from Annex A of the WHO HIA report. This table illustrates the relative risks of respiratory and other diseases and health endpoints associated with increasing air pollution.
| HEALTH ENDPOINT | Incidence per 100 000 |
PM10 24h ave. RR |
PM2.5 24h ave. RR |
SO2 24h ave. RR |
O3 8 hr max. RR |
O3 1 hr max. RR |
NO2 daily average RR | NO2 1 hr max. RR |
|---|---|---|---|---|---|---|---|---|
| MORTALITY | ||||||||
| Total mortality | 1013 | 1.0074 | 1.015 | 1.004 | 1.0051 | 1.0046 | 1.003 | |
| Cardiovascular Mortality | 497 | 1.008 | 1.008 | 1.004 | 1.004 | 1.002 | 1.002 | |
| Respiratory Mortality | 66 | 1.012 | 1.01 | 1.0126 | 1.008 | |||
| MORBIDITY | ||||||||
| Hospital Admissions Respiratory Disease | 1260 | 1.008 | ||||||
| Hospital Admissions Respiratory Dis. <15 Yrs | 100 | |||||||
| Hospital Admissions Respiratory Dis 15-64 yrs | 66 | 1.0018 | 1.0062 | 1.0038 | 1.002 | 1.0008 | ||
| Hospital Admissions Respiratory Dis 65+ Years | 1.004 | 1.0076 | 1.0062 | 1.0038 | 1.001 | |||
| Hospital Admissions Asthma <15 Years | 100 | 1.015 | 1 | 1.0012 | 1.0062 | 1.0024 | ||
| Hospital Admissions Asthma 15-64 Years | 66 | 1 | 1.007 | 1.003 | 1.0058 | 1.0022 | ||
| Hospital Admissions COPD | 101.4 | 1.0044 | 1.0086 | 1.0068 | 1.0038 | 1.0026 | ||
| Hospital Admissions Cardiovascular Disease | 436 | 1.009 | ||||||
| Hospital Admissions Congestive Heart Elderly | 122 | |||||||
| Acute Myocardial Infarction | 132 | 1.0064 | 1.0036 | |||||
| Acute Bronchitis < 25 Yrs | ||||||||
| Asthma Attacks Children | 1.051 | |||||||
| Asthma Attacks Adults | 1.004 | |||||||
| a) The relative risk estimates are based on Western European data only. The analysis was based on air quality and health endpoint data from 141 cities in 30 countries in Europe, with a total population of 78 million, 25% of the total urban population of the European Region of the WHO.iii | ||||||||
The proportion of the health impact (Total mortality, asthma attacks in children, etc.) attributable to a given exposure (pollutant-time combination) in a given population may be calculated using:
AP = SUM{[RR(c) - 1] * p(c)}/ SUM [RR(c)*p(c)] (1)
where: RR(c) is the relative risk for the health outcome in category c of exposure,
p(c) is the proportion of the population in category c of the exposure and
AP is the Attributable Proportion (of the health outcome to the given exposure).
The number of cases IE attributable to exposure to air pollutants, for a baseline frequency I of the selected health outcome may be calculated from:
IE = I*AP. (2)
The estimate of the number of cases (for a given pollution level) is thus clearly dependent on the baseline frequency and the relative risk factors; both these factors may vary from city to city or country to country.
The data given in Table 1 are based on studies in Europe. Baseline incidence and Relative Risk values may be different in regions and/ or different populations, and may be different in South African cities, and may be different within different areas of a city. Nevertheless, this approach to health impact assessment may provide a systematic method for estimating breakpoints for the different pollutant-averaging time combinations. These tables imply that the relative risk is constant for a constant increment (10 µg/m3) in pollution levels.
