Chemicals are widely used in the control of diseases. Persistent organic pollutants (POPs) are used in vector control for diseases such as malaria. Pesticides such as dichlorodiphenyltrichloroethane (DDT) are used primarily to control malaria as well as in the veterinary sector to control plague-transmitting fleas and trypanosomiasis- transmitting tsetse flies (Mörner and others 2002). The use of these chemicals presents special challenges for Africa; the negative environmental impacts need to be weighed against the gains made from disease control.

Figure 7: Population at risk from malaria The high incidence of some diseases is not just a challenge in relation to mortality levels, but also threatens economic prospects. Malaria for example is still a primary killer in Africa (see Figure 7 for populations at risk). In 2001, there were an estimated 270-480 million cases per year with approximately 900 000 people dying from the disease annually (WHO/AFRO 2001). Malaria has slowed annual economic growth by 1.3 per cent, imposing a loss of US$12 000 million on the region per year (RBM/WHO 2003). Despite the environmental threats it poses, DDT has been the most cost-effective and efficient way of controlling malaria. This is the main justification for its continued use and its exemption under the Stockholm Convention until such time that alternatives are found. South Africa’s experience is illustrative. When South Africa stopped using DDT in 1996, the number of malaria cases in the KwaZulu- Natal province rose from 8 000 to 42 000 by 2000 (Tren and Bate 2004). South Africa tried various alternatives but they proved less effective. Since reintroducing DDT, it has been able to reduce the number of deaths in the province to less than 50 per year (Tren and Bate 2004).

However, while DDT is important for disease control, there are concerns that its continued use constitutes a health risk especially for countries with limited chemical management infrastructure. DDT has also been found to bioaccumulate especially in aquatic species including crayfish, prawns and fish, and in this way poses a further threat to human health. With climate change, the incidence and range of malaria is predicted to increase (see Chapter 1: The Human Dimension) potentially increasing the need for the continued use of this highly toxic chemical.


Pollution places freshwater systems at risk and threatens the availability of safe water for human consumption, by disrupting essential ecosystem services. Ecosystems provide effective mechanisms for cleansing the environment of wastes; this service is now overtaxed in many settings, leading to local and sometimes global waste accumulation (MA 2006). Well- functioning ecosystems absorb and remove contaminants. For example, the role played by wetlands in maintaining freshwater quality by the removal of excess nutrients is well-established. As the Millennium Ecosystem Assessment (MA) notes, these systems are under threat and this poses new challenges for management (MA 2006):

  • Where excessive wastes are discharged into ecosystems, ecosystems are unable to cope and waste treatment technologies are required to restore or preserve ecosystem balance, and thus reduce or eliminate the risks to human health.
  • Recycling can be an important environmental management strategy, however where waste contains POPs or heavy metals, recycling can lead to the accumulation of these pollutants and increased human exposures through food and water.

Meeting water needs is a priority for Africa, and countries have agreed, in terms of the MDGs and the Africa Water Vision 2025, to increase the number of people with access to safe water (see Chapter 4: Freshwater). The lack of safe water poses a major threat to human well-being. In 2002, 303 million people across Africa still did not have access to safe water (WHO and UNICEF 2004). The lack of access to safe water is a product of many factors including increasing pressure on limited resources by population growth and a lack of priority given to this issue. Access to safe water varies within countries, with poor and rural people being at the greatest disadvantage. For example, in Congo, 77 per cent of city and town dwellers have access to safe drinking water but only 17 per cent of rural inhabitants do (TWAS 2002). About 627 000 children die annually from diarrhoeal illnesses, related to a large extent to unsafe drinking water (Gordon and others 2004).

Inorganic chemical compounds and POPs in food and water present risks to people. Such contamination may be the result of natural processes (as in the case of fluoride or arsenic contamination of water sources) or from human releases of toxic chemicals into the environment (through, for example, pesticide use). In small quantities fluoride is good for teeth, however in high concentrations it destroys teeth and accumulates in bones resulting in crippling skeletal damage (Gordon and others 2004). Because they are still growing, children are at highest risk (Gordon and others 2004). As of 2004, cases of dental and skeletal defects have been reported in Ethiopia, Eritrea, Kenya, Niger, Nigeria, South Africa, Sudan, Tanzania and Uganda (Gordon and others 2004).

Inorganic nitrogen pollution of inland waterways has more than doubled globally since 1960 and increased by a factor of over ten for many industrialized parts of the world (MA 2006, UNEP 2002). As already noted, pollution impairs the ability of ecosystems to provide clean and reliable sources of water. Deterioration of freshwater quality is magnified in cultivated and urban systems (due to high use and high pollution sources) and in dryland systems (due to high demand for flow regulation and absence of dilution potential) (MA 2006). This is particularly significant for Africa, given the extent of drylands within the region (see Chapter 3: Land).

There is also an increasing presence of pharmaceutical products or residues in the environment from sewage and solid waste discharges, however the health risks these chemicals pose have not yet been quantified (WWF 2004a, MA 2005).

In addition to the threats posed by pollutants, water quality is also affected by pathogens, which fall into three general categories: bacteria, viruses and parasitic protozoa. Bacteria like Vibrio cholerae, Salmonella typhii and several species of Shigella routinely inflict serious diseases such as cholera, typhoid fever, and bacillary dysentery, respectively. Chemicals can play an important role in the treatment of water against such pathogens.

Given the general non-availability of piped water to homes people have to collect water from shared wells, rivers or community access points. Many people are forced to use old containers for collecting water. Due to a lack of awareness, agricultural chemical containers are often used and illness can often result.