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Medical Geology is defined as the science dealing with the relationship between geological factors and health problems in humans, animals and plants. It is an emerging interdisciplinary scientific field studying the relationship between natural geological factors and their effects on human and animal health.The Commission on Geological Sciences for Environmental Planning defines medical geology as, “The science dealing with the influence of ordinary environmental factors on the geographical distribution of health problems in man and animals. There is a body called The International Medical Geology Association (IMGA) which aims at providing a network and a forum to characterize the properties of geological processes and agents, the dispersal of geological material and their effects on human populations and there are a series of conferences called MEDGEO that are held by IMGA once in every two years.

1.Branches of Medical Geology
Medical geology can be split into two primary branches based on the number and variability of element sources within the environment. The first branch is strictly related to the natural occurrence of elements in the geologic environment (e.g., ingestion of food grown in soils with either element deficiencies or toxicities), whereas the second branch relates to elemental occurrence relative to natural hazards (e.g., earthquakes, volcanic eruptions, flooding and landslides)

2.Geology
The geology of an area has a direct impact on the regional input of elements into the soil, air and water. In turn, these inputs, depending on composition, may result in adverse health effects in humans, animals and/or plants. Health issues related to a region’s geology are visible in both humans and animals on almost every continent. The diverse geographical and geochemical source of human foods in developed nations creates a “homogenized diet” reflecting materials grown on a range of soil types, each with different chemical characteristics and potentially imported from a number of countries. As a result of this complex sourcing mechanism, element deficiencies or toxicities are generally rare in regards to dietary intake. Additionally, element imbalances in the soil are often amended before the growth of crops, thus eliminating any subsequent problems. Thus, trace element deficiencies and/or toxicities that are a result of geological conditions are much easier to identify in animals and people in developing countries since much of the food and water ingested is obtained directly from the surrounding environment.

According to Davies T.C.2010, a large body of evidence points to significant health effects resulting from our interactions with the physical environment and we continue to recognize 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 formalize their study. Africa is a continent with a diverse geography, characterized by a range of altitudes, a peculiar hydrological network created in part by the formation of the Great Rift Valley on the eastern flank and arid lands typified by the Sahara and the Mega Kalahari. Volcanic activity accompanying rifting and formation of most of the highlands and mountains has released various trace elements, mostly above background levels, into the environment. A unique distribution pattern of these elements has developed in more recent geological times, following pronounced separation due to extreme tropical conditions of weathering, 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 location. 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 geochemical factors on the distribution of diseases in man and animals.

3.Selected Studies on Medical Geology
There are various studies on medical geology which include, but not limited to environmental geochemistry and human health, water and human health, soil pollution and remediation, atmosphere pollution and human health. Studies associated with analytical methodology, medical geology in toxicology and epidemiology, medical geology, public health and regulatory sciences just to mention but a few. The geology and tectonic characteristics constitute an appropriate environment for the presence of toxic and heavy metals. The rapidly expanding field of medical geology deals with the relationships between natural geological factors and health, both human and animal. It also aims to improve our understanding of the ways in which the geological environment has an impact on the geographical distribution of health problems. There have been books from the work of various cross cutting geoscientists and medical/public health researchers that have addressed health problems caused, by geological materials ( atmospheric dust, lapilli tuffs/volcanic ash,minerals, rocks, and water) and processes earthquakes). Among the environmental health problems discussed in the volume are: human and animal exposure to toxic levels of trace essential and non-essential elements such as mercury, arsenic, trace element deficiencies; exposure to natural dusts and to radioactivity; naturally occurring organic compounds in drinking water; and the effects of volcanic emissions. Examining the positive side of the equation as well as the negative, the book also deals with the many health benefits of geologic materials and processes. It provides examples from different continents as well as a state-of-the-art review of the latest developments in the medical geology. The authors are all recognized geoscientific and medical experts working in the fields of geology, geochemistry, pathology and medicine, veterinary, biology etc.

In trying to highlight an example where medical geology has made an impact, there have been high levels of geogenic cadmium (Cd) found in some soils of Jamaica, particularly in the central part of the island. The potential health impact on residents who consumed foods grown on these soils was determined and food which have shown the greatest affinity for Cadmium uptake are mainly green leafy ones. Besides, the tropical terrains of the Indian subcontinent and the neighboring regions also provide some of the best examples in medical geology where the impact of the geosphere on human health is markedly seen and identified. The impact of the natural environment on human health has been a subject of study in China for thousands of years to date. China’s varied geology and geography and its large population living off the land have resulted in the presence of virtually every known environmental health problems related to medical geology.

There is a close relationship between medical treatment and geology. Worldwide, there are more than 10 million new cancer cases each year, and cancer is the cause of approximately 12% of all deaths. Given this, a large number of epidemiologic studies have been undertaken to identify potential risk factors for cancer, amongst which the association with trace elements has received considerable attention. Trace elements, such as, arsenic, cadmium, selenium, zincand nickel, are found naturally in the environment, and human exposure derives from a variety of sources, including air, drinking water, and food. Trace elements are of particular interest given that the levels of exposure to them are potentially modifiable. In this review, we focus largely on the association between each of the trace elements noted above and risk of cancers of the lung, breast, colorectum, prostate, urinary bladder, and stomach. Most studies have reported no association between selenium and risk of breast, colorectal, and stomach cancer, and between zinc and prostate cancer risk. There is compelling evidence in support of positive associations between arsenic and risk of both lung and bladder cancers, and between cadmium and lung cancer risk.

In another example where medical geology has been applied is the increasing use of pesticides and chemical fertilizers, especially the fertilizers with nitrates compounds, which have been common for the increased production of agricultural crops, has caused the nitrate pollution in the (soil, water, and environment). They have caused a lot of damage to humans and animals. Accumulation of nitrates in different kind of vegetables such as; green pepper, tomatoes, egg plants, watermelon, cucumber, and red pepper have been studied in some geographical areas and analysis of the samples was sent to the soil and water laboratory. The final results from the chemical analysis of samples showed that the mean levels of nitrates from the samples of the fruit crops in the those areas were all lower than the critical levels but from nutritional point of view it is argued that these quantities of dry matter do not constitute a health problem in humans.

In ecotoxicology and Environmental studies carried out in fast developing cities in China, risks related to heavy metal pollution in urban construction dust fall were highlighted. There is high metal pollution levels of road construction, there is a significant correlation of lead and zinc metals in road construction dust. The studies also showed that metals in construction dust fall pose higher ecology risks even at Wuhan.

All of the above studies show that knowledge of geology and geomorphology is essential to understanding, and thus eradicating, or preventing, a range of environmental health problems.

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