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Chapter Two: The State of the Environment - Global issues

Human health and the environment

The World Health Organization estimates that poor environmental quality contributes to 25 per cent of all preventable ill-health in the world today (WHO 1998). Traditional problems, such as contaminated water, poor sanitation, smoky indoor air and exposure to mosquitoes and other animal disease vectors, are still the primary environmental factors in ill health. Across the world, insufficient water supplies, inadequate sanitation and poor hygiene are primarily responsible for global outbreaks of cholera and other diarrhoeal diseases, which claim three million lives each year (WHO 1997a).

 Environmental factors affecting health
  Polluted air Poor sanitation and waste disposal Polluted water or poor water management Polluted food Unhealthy housing Global environmental change

Acute respiratory infections *       *  
Diarrhoeal diseases   * * *   *
Other infections   * * * *  
Malaria and other vector-borne diseases   * *   * *
Injuries and poisonings *   * * * *
Mental health conditions         *  
Cardiovascular diseases *         *
Cancer *     *   *
Chronic respiratory diseases *            

Source: WHO 1997a


 Population with and without sanitation, all developing countries

(Click image to enlarge)

Source: WHO 1997b

Inadequate sanitation is one of the prime causes of disease. In the developing countries, the provision of sanitation is not keeping up with population growth

Vector-borne diseases, affecting more than 700 million in total a year, are considered the most sensitive to climatic and environmental conditions. Malaria, the best-known vector-borne disease, has been declared 'public enemy number one' by WHO and affects more than 500 million people in 90 countries, causing 1.5-2.7 million deaths per year (WHO 1997a).

In many developing regions, these traditional environmental health problems are now exacerbated by emerging problems of pollution from industry and agriculture (Smith 1997). Chemical agents, particularly air-borne ones, are considered to be major factors in causing and worsening tuberculosis, bronchitis, heart disease, cancers and asthma. Tuberculosis, the single largest cause of death in adults from infectious diseases, was responsible for three million deaths in 1996, 95 per cent of which occurred in the developing world (WHO 1997a). Exposure to pesticides, fertilizers and heavy metals poses health risks through soil, water, air and food contamination. Global pesticide use has resulted in 3.5-5 million acute pesticide poisonings per year (WHO 1990). Recent epidemiological studies have suggested a link between organochlorine pesticides and cancer, including lymphoma and breast cancer (Zahm and Devesa 1995 )

The emergence of some 30 new diseases, including AIDS, Ebola and haemorrhagic illnesses, in the past 20 years has become a growing public health issue. Demographic changes, in particular rapid, unplanned urbanization, have resulted in conditions that encourage the spread of diseases such as dengue fever. The two primary mosquito vectors of the dengue, Aedes aegypti and Aedes albopictus, have adapted from their natural forest environments, where they breed in tree holes containing rainwater, to the urban environment where they breed in drains, water cans, discarded tyres, pots and bottles (Gubler and Clark 1994).

Urbanization can be an important source of health problems: nearly half of the world's population will live in urban centres by the end of the 20th century but currently 30-60 per cent of the urban population are in low-income countries, and lack adequate housing with sanitary facilities, drainage systems, and piping for clean water (UNCHS 1996). This number is expected to increase since local and city authorities often lack the resources, knowledge, trained personnel and financial capacity needed to meet their responsibilities in providing services and amenities essential for healthy living. Increased exposure to biological and chemical health risks in urban areas is particularly harmful to children. Children suffer the greatest number of deaths due to diarrhoeal diseases (2.5 million deaths per year) and this number is likely to increase in populations of the urban poor. Prevalence of asthma, often exacerbated by air pollutants, has also increased among children (Woolcock and Peat 1997). Studies suggest a quantitative relationship between atmospheric carcinogen levels and lung cancer, and WHO has estimated that 50 per cent of the global burden of chronic respiratory illnesses is associated with air pollutants (WHO 1997b).

As the global population continues to grow, there is increasing pressure to develop agriculture, roads and transportation systems in previously unsettled areas. This kind of land conversion can encourage the spread of diseases harmful to human health. For example, leishmaniasis, an infectious disease transmitted through a sandfly bite, has increased to 12 million cases (WHO 1998) each year alongside increasing land development in Africa, Latin America and West Asia (WHO 1997b). Forest clearance in particular is associated with higher incidence of diseases such as malaria.

People in developing countries face larger amounts of indoor pollutants, such as sulphur and nitric oxides and arsenic compounds, due to greater exposure to open fires which burn biomass, coal or wood as fuel. Indoor pollution, a more severe threat to women and children who spend more time indoors, causes respiratory disorders and is also linked to heart and lung disease mortality. A study in India and Nepal demonstrates that cardiovascular disease is more common among women who have been exposed to indoor pollutants (WHO 1992).

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