The genesis of what has evolved into Medical Geology can be traced back to the realization of the environmental factor as one of the causal factors affecting health although, according to Finkelman et al. (2001), the impacts of geologic materials on human health have been recognized for thousands of years. This developed in response to apprehension of environmental degradation arising out of anthropogenic impacts resulting from industrial technology. Silent Spring (Carson, 1962) is the earliest expression of this apprehension has come to be defined by the health and environment cause-effect framework given in Fig. 1 below by WHO (2000).
These adverse or toxicological effects on health from the environment arise from poor air, water and soil quality as a result of contamination. In fact, the emergence of toxicology as an independent scientific discipline is a result of the effects on health from the environment. Natural materials also form the foundation of modern civilization and are crucial for almost every aspect of modern living. This interaction with natural materials is often viewed as harmless (Finkelman et al., 2001). However, some geologic materials pose significant health risks that jeopardize individuals, communities and even whole populations (Geotimes Staff, 2001)
Therefore, health effects, indicated by changes in longevity and functionality, arising from the environment imperatively require environmental stewardship through the study of earth materials and processes. In fact, Time magazine wrote in January 1989 that humans were threatening the state of the Earth's environment and declared it an endangered planet which making it more exigent on medical geology to supply solutions to health treats. The assessment of the influence of natural and anthropogenic earth science factors, according to Centeno et al. (2003), on the geographical distribution of a wide range of human and animal diseases has commenced.
MEDICAL GEOLOGY AS ENVIRONMENTAL STEWARDSHIP
In traditional medical practice, according to by Moeller (1997), physicians deal with patients according to the model given in Fig. 2. In this clinical interventional model the intercession comes in the diagnosis and treatment of a disease to cure the patient. This affords intervention but no control over the disease to enable elimination of its source or cause before infection.
The environment health stresses need to be tackled to enable a measure of control of diseases arising from environmental factors. Traditionally these pre-emptive measures are taken under public health [branch of medicine dealing with safeguarding and improving community health through organized community effort involving prevention of disease, control of communicable disease and health education (Academic Press Dictionary of Science Technology)] including epidemiology. Moeller (1997) describes this practice according to the model given in Fig. 3.
Public health intervention seeks to establish some degree of control over sources of risks to human health and well being. However, this does not afford sufficient control as the causes and sources themselves are not addressed. The ability to exercise greater control lies in the field of environmental health which is defined by Pew Environmental Health Commission (2001) as comprising those aspects of human health, including quality of life, that are determined by interactions with physical, chemical, biological and social factors in the environment. It also refers to the theory and practice of assessing, correcting, controlling and preventing those factors in the environment that may adversely affect the health of present and future generations. This control according to Moeller (1997) is as in Fig. 4.
Environmental stewardship prevents environmental degradation and consequences for human health. The advantages are obvious as it reduces the risk factors in the environment. Medical Geology is concerned with the materials affecting public health and processes responsible for their behavior and distribution encompasses environmental stewardship.
Stewardship represents the underpinnings of Medical Geology which that also needs to be cast in a scientific and academic framework. An outline this is proposed below.
MEDICAL GEOLOGY CONCERN IN UNDERSTANDING EARTH SYSTEMS
The Earth System
A system is defined as a set of objects with relationships between them and their attributes or also as a set of interdependent elements forming a collective entity. The Earth may be considered as a system and the components and their interconnections are shown in Fig. 5 below.
The understanding of this Earth System is sought for the purpose of intervention and control in order to prevent or intervene to arrest menace to public health. This involves the characterization and clarification of the components and processes achieved through the earth sciences which are directed towards environmental stewardship. Medical Geology is concerned with the understanding of how the geological, physical and biological processes of the Earth System are functionally interrelated including the geological-physical-biological interactions.
The Source-Pathway-Target Concept.
The effective practice of environmental stewardship using the Source-Pathway-Target concept (Holdgate, 1979), as shown in Fig. 6, requires erecting impedance between the Source, Pathway and Target for intervention and control as shown in Fig. 7.
Medical Geology aims at proving this stewardship in insuring that the source of harmful materials is capped. It does seem paradoxical to have clinical or public health intervention, as mentioned above, when the source is not controlled. This assures optimum intervention and control that lies in ensuring that the source, in the first instance, does not emanate harmful materials and the pathways available, secondarily, are checked.