Some Environmental Problems of Geomedical Relevance in East and Southern Africa

Medical geology studies the influence of geo-environmental factors on the geographical distribution of diseases of humans and animals. In the east and southern African subregion, there has been little attention paid to date on the extent to which these factors may be important in disease causation, even though developing countries in general can be shown to hold tremendous promise for specific research in this field. This chapter highlights some problems of geomedical relevance in the subregion and submits that interdisciplinary research among scientists can help provide practical solutions. The iodine deficient regions of east and southern Africa have been identified and the widespread occurrence of goiter and related conditions, collectively referred to as iodine deficiency disorders (IDD), firmly established (e.g., Davies 1994, Jooste et al. 1997). These are serious and debilitating consequences, particularly for poor populations, as the capacity of children is severely restricted and they become a burden to the family. The reported geographical distribution of endemic goiter in East Africa is shown in Figure 22.1. Many aid agencies and governments have attempted to solve the problem by increasing dietary intake of iodine via the introduction of iodized salt and iodized oil programs. Despite these interventions, IDD remain a major problem in the subregion. It is likely that IDD are multi-causal diseases involving factors such as trace element deficiencies, goiter-inducing substances in foodstuffs (known as goitrogens), and genetics (Fordyce 2000). However, geochemists have an important role to play in determining the environmental cycling of iodine and its uptake into the food chain if levels of dietary iodine are to be enhanced successfully. It has now been established that excessive fluorine (mainly in the form of fluoride) is present in parts of the hydrological system of Kenya as well as other countries in the subregion, particularly those that are associated with rift formation (Gaciri and Davies 1993). Fluoride in minor amounts (around 1.3 ppm) reduces dental decay and enhances the proper development of the bone. A similar level of fluoride intake may also be beneficial to animals.