Medical Geology in Africa

Abstract

A large body of evidence points to signifi- cant health effects resulting from our interactions with the physical environment and we continue to recog- nise connections between geological materials and processes and human and animal disease. In Africa, these relationships have been observed for many years, but only recently have any real attempts been made to formalise their study. Africa is a continent with a diverse geography, characterised by a range of alti- tudes, a peculiar hydrological network created in part by the formation of the Great Rift Valley on the east- ern flank and arid lands typified by the Sahara and the Mega Kalahari.Volcanic activity accompanying rifting and formation of most of the highlands and moun- tains has released various trace elements, mostly above background levels, into the environment. Aunique dis- tribution pattern of these elements has developed in more recent geological times, following pronounced separation due to extreme tropical conditions of weath- ering, leaching and eluviation. It is therefore possible to delineate large areas of the continent containing element deficiencies or toxicities, which are closely related to the local geology and/or geographical loca- tion. In a region where rural communities are still largely dependent on water and food sources that are locally derived, the above setting provides an attractive opportunity for studying the influence of geochemi- cal factors on the distribution of diseases in man and animals. This pursuit constitutes a large part of the study of the rapidly emerging science of “medical geology”. According to this definition, the influence of the indoor environment, for example in factories and offices, thus falls outside the scope of medical geology and comes within the area of occupational medicine. To attain completeness in the present review, however, industrially derived exposure to known toxic elements (originating from mining or ore processing, such as are contained in mineral dust, for instance) is also briefly considered. Of the elements for which there are proven or suspected direct causal relationships with man’s health, significant data exist for fluorine, iodine, silicon, arsenic and certain trace metals (bothmicronu- trients and potentially harmful elements). The reader is presented with a summary of available informa- tion including current hypotheses and an illustration of why improved understanding of these relationships, based on interdisciplinary studies, would lead to better diagnoses and therapy.