Eiliv Steinnes, Department of Chemistry, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
Geomedicine is the science dealing with the influence of natural factors on the geographical distribution of problems in human and veterinary medicine. Discussions on potential harmful impacts on human and animal health related to soils are frequently focused on soil pollution. However, problems related to natural excess or deficiency of chemical substances have been known for a long time and may be even more important in a global perspective. Most attention in this respect has been related to essential or toxic trace elements. Particularly problems related to trace element deficiencies in soils have been frequently reported over the years in cultivation of agricultural crops as well as in breeding of domestic animals. Deficiencies in plants are often observed for boron, manganese, copper, zinc, and molybdenum. In domestic animals deficiency problems related to cobalt, copper, iodine, manganese, and selenium are well known. Toxicity problems in animals exposed to excess intake have been reported e.g. for copper, fluorine, and selenium. Sometimes interactions between elements may create specific problems, such as copper deficiency in cattle occurring with excess supply of molybdenum. In modern agriculture trace element deficiencies are balanced by including these micronutrients in fertilizers or animal feed. Moreover adjustment of soil pH may beneficially regulate their uptake in crops. Problems in veterinary medicine related to essential trace elements have therefore largely been solved in developed countries. A possible exception is organic farming where trace element deficiency problems in farm animals seem to be on their way back. Human beings are similar to mammals in their relations to trace elements and thus likely to develop corresponding problems as observed in domestic animals if their supply of food is local and dependent on soils providing trace element imbalances in food crops. In developed countries the human population derive their foods from a variety of different geographical areas and are thus not likely to be much influenced by geographical differences in soil chemistry. In large parts of Africa, Asia, and Latin America however people depend on locally grown food, and contemporary geomedical problems in man are therefore mainly restricted to these parts of the world. Well-known examples are the Keshan disease in China associated with selenium deficiency and the large-scale arsenic poisoning in Bangladesh and adjacent parts of India. However, the list of such problems is considerably longer, and it seems reasonable to assume that many problems in developing countries related to geomedical factors are still undetected. Not all essential elements in soils are derived only from the soil minerals. Some trace elements such as boron, iodine, and selenium are supplied in significant amounts to soils by atmospheric transport from the marine environment, and disorders associated with these elements are therefore historically less common in coastal areas than further inland. The current occurrence of iodine deficiency disorders in humans is mainly restricted to land areas situated far from the ocean, and it may be noted that the areas in China with problems related to the Keshan disease are also predominantly located far from the sea.