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Medical Geology is a multi-disciplinary field of study in geology which studies the health effects of geologic materials and processes on humans. Such health effects can be good, or possibly hazardous. Medical Geology integrates professionals from medicine, geography and geology to handle problems accruing from the geology of an area. Three aspects of geology are relevant for a comprehensive study of health problems arising from the geology of a particular environment, namely: mineralogy, geochemistry and hydrogeology. Hazardous effects are caused by the excessiveness or deficiency of essential and non- essential trace elements such as: As, F-, I- , Se, Rn, Mn, Cd and Pb. For instance, excessiveness of arsenic in coals in China has lead to a toxic effect called arsenosis– the ulceration of the hands and feet; deficiency of iodine in the soil leads to goiter –the enlargement of the thyroid gland, while the excessiveness of fluoride in rocks leading to various forms of fluorosis which can manifest in the dissolution of apatite crystals of the enamel. This multidisciplinary field of geology also probes into the benefits and banes of eating soil, clay and shale –a practice called geophagy. Through the study of Medical Geology, however, some geologic materials have been found useful in the pharmaceutical, medical and cosmetic industries. These include medicinal/mineralized waters applied in the treatment of various skin diseases, such as rashes and eczema, as they contain elements such as Na, Ca, Mg, Cl, K, I, Br and Fe. Bathing in such mineralized waters―a process called balneotherapy―helps in taking these elements into the body through osmosis. Alkaline water production using tourmaline (Ca, K, Na)(Al, Fe, Li, Mg, Mn)3(Al, Cr, Fe, V)6(BO3)3(Si, Al, B)6O18(OH, F)4, and zeolite (Na2Al2Si3O10.2H2O ) is another important application of Medical Geology. Alkaline water negates the Oxidation-Reduction Potential of body toxins and increases the body pH up to 8. As most processed foodstuffs are acidic, the intake of alkaline water will raise the alkalinity of the body leading to increased longevity. Kaolin and bentonite –the healing clays– are applied in the treatment of gastrointestinal diseases; they have net negative surface charges with which they attract toxins. Toxins are then adsorbed into the structure of the clay mineral, and thus removed. Medical Geology also has important application in the manufacture of plaster of Paris. It is produced by calcining gypsum to produce a strong material used in holding fractured anatomical structures of the body in place until healing is completed. Production of milk of magnesia from brucite [Mg(OH)2]―magnesium hydroxide―is another important application of Medical Geology. Milk of magnesia is an antacid and interferes with the adsorption of folic acid in the stomach; it helps in maintaining the stomach pH and in the detoxification of the stomach.

Medical geology is a multi-disciplinary field of study in geology which studies the health effects of geologic materials and processes on humans. Such health effects can be good, or possibly hazardous. Medical geology integrates professionals from medicine, geography and geology to handle problems accruing from the geology of an area. Three aspects of geology are relevant for a comprehensive study of health problems arising from the geology of a particular environment, namely: mineralogy, [[geochemistry]], and hydrogeology.  

 

Hazardous effects are caused by the excessiveness or deficiency of essential and non-essential trace elements such as: As, F-, I- , Se, Rn, Mn, Cd and Pb. For instance, excessiveness of arsenic in [[coal]] in China has lead to a toxic effect called arsenosis—the ulceration of the hands and feet; deficiency of iodine in the soil leads to goiter—the enlargement of the thyroid gland, while an excess of fluoride in rocks leads to various forms of fluorosis which can manifest in the dissolution of apatite crystals of the enamel.  

 

This multidisciplinary field of geology also probes into the benefits and banes of eating soil, clay, and shale—a practice called geophagy. Through the study of medical geology, however, some geologic materials have been found useful in the pharmaceutical, medical, and cosmetic industries. These include medicinal and mineralized waters applied in the treatment of various skin diseases, such as rashes and eczema, as they contain elements such as Na, Ca, Mg, Cl, K, I, Br and Fe. Bathing in such mineralized waters―a process called balneotherapy―helps in taking these elements into the body through osmosis. Alkaline water production using tourmaline (Ca, K, Na)(Al, Fe, Li, Mg, Mn)3(Al, Cr, Fe, V)6(BO3)3(Si, Al, B)6O18(OH, F)4, and zeolite (Na2Al2Si3O10.2H2O) is another important application of Medical Geology. Alkaline water negates the Oxidation-Reduction Potential of body toxins and increases the body pH up to 8. As most processed foodstuffs are acidic, the intake of alkaline water will raise the alkalinity of the body leading to increased longevity. Kaolin and [[bentonite]]-–the healing clays–-are applied in the treatment of gastrointestinal diseases; they have net negative surface charges with which they attract toxins. Toxins are then adsorbed into the structure of the clay mineral, and thus removed. Medical Geology also has important application in the manufacture of plaster of Paris. It is produced by calcining [[gypsum]] to produce a strong material used in holding [[fracture]]d anatomical structures of the body in place until healing is completed. Production of milk of magnesia from brucite [Mg(OH)2]―magnesium hydroxide―is another important application of Medical Geology. Milk of magnesia is an antacid and interferes with the adsorption of folic acid in the stomach; it helps in maintaining the stomach pH and in the detoxification of the stomach.

==Introduction to medical geology==

==Introduction to medical geology==

Rocks are the fundamental building blocks of the Earth’s surface, containing a multitude of minerals and chemical elements. These rocks are broken down by weathering processes which restructure the minerals to form the soils on which crops and animals are raised.<ref name=Setal2001>Selinus, O., J. A. Centeno, R. B. Finkelman, P. Weistein, and E. Derbyshire, 2001, Earth and Health– building a safer environment. Planet Earth, 1, 1-16.</ref> Through the consumption of plants and animals− i.e. the food chain− man comes in contact with those elements originally in the rocks. Should the rock/soil be deficient in a particular element such as iodine, the effect would manifest as adverse health effects on the consumers. On the other hand, if there is excess concentration of a particular element such as arsenic in the rock/soil, the health of the consumer is equally at risk.<ref name=S&F2011>Selinus, O. and R. B. Finkelman, 2011. Geochemical Aspects of Medical Geology. Journal of the Geological Society of Sri Lanka, 14, 01-09.</ref>

Rocks are the fundamental building blocks of the Earth’s surface, containing a multitude of minerals and chemical elements. These rocks are broken down by weathering processes which restructure the minerals to form the soils on which crops and animals are raised.<ref name=Setal2001>Selinus, O., J. A. Centeno, R. B. Finkelman, P. Weistein, and E. Derbyshire, 2001, Earth and Health—building a safer environment: Planet Earth, v. 1, p. 1–16.</ref> Through the consumption of plants and animals—i.e. the food chain—man comes in contact with those elements originally in the rocks. Should the rock/soil be deficient in a particular element such as iodine, the effect would manifest as adverse health effects on the consumers. On the other hand, if there is excess concentration of a particular element such as arsenic in the rock/soil, the health of the consumer is equally at risk.<ref name=S&F2011>Selinus, O. and R. B. Finkelman, 2011, Geochemical aspects of medical geology: Journal of the Geological Society of Sri Lanka, v. 14, p. 1–9.</ref>

The intake of contaminated groundwater exposes the consumer to the risk of injecting harmful elements into the body system. Groundwater is made available to man as springs, rivers, lakes and through man-made wells.

The intake of contaminated groundwater exposes the consumer to the risk of injecting harmful elements into the body system. Groundwater is made available to man as springs, rivers, lakes and through man-made wells.

Volcanism is another geologic process that poses potential harm to human health, ejecting tons of different poisonous gases and volcanic ash. These travel kilometers round the planet to be inhaled by people at different radii from the vent thereby causing diverse toxicity problems in the victims.<ref name=Skinner>Skinner, H. C. W., 2007, The Earth,Source of Health and Hazards: An Introduction to Medical Geology. Annual Review of Earth and Planetary Sciences, 35,177–213.</ref>

Volcanism is another geologic process that poses potential harm to human health, ejecting tons of different poisonous gases and volcanic ash. These travel kilometers round the planet to be inhaled by people at different radii from the vent thereby causing diverse toxicity problems in the victims.<ref name=Skinner>Skinner, H. C. W., 2007, The Earth, a source of health and hazards: An introduction to medical geology: Annual Review of Earth and Planetary Sciences, v. 35, p. 177–213.</ref>

In addition, dust from deserts is a source of health hazard to man. The harmattan season for example, comes with moments of increased asthma torments and various sorts of nasal difficulties such as catarrh as it has the potential to transport soil pathogens to distant regions. It has been confirmed that dust from the Sahara travels across the Mediterranean Sea to the hinterlands of Europe and to North America.<ref name=Sel2004>Selinus, O., 2004. Medical Geology: An Emerging Specialty. Terrae, 1(1), 8-15.</ref>

In addition, dust from deserts is a source of health hazard to man. The harmattan season for example, comes with moments of increased asthma torments and various sorts of nasal difficulties such as catarrh as it has the potential to transport soil pathogens to distant regions. It has been confirmed that dust from the Sahara travels across the Mediterranean Sea to the hinterlands of Europe and to North America.<ref name=Sel2004>Selinus, O., 2004: Medical geology: An emerging specialty: Terrae, v. 1, no. 1, p. 8–15.</ref>

Medical geology, therefore, is a developing multidisciplinary collaboration that curtails the health effects arising from the various geologic materials and processes of an area, because the environment in which man lives affects the health of man.<ref name=Sel2004 />

Medical geology, therefore, is a developing multidisciplinary collaboration that curtails the health effects arising from the various geologic materials and processes of an area, because the environment in which man lives affects the health of man.<ref name=Sel2004 />

However, the above-mentioned issues are not the total range of medical geology. It is also interested in the use of geologic materials to cure various kinds of diseases. This has led to researches into the use of clay minerals for therapeutic purposes. It has also launched profound research into the use of mineralized thermal waters for the treatment of various diseases. These efforts have yielded laudable results over many decades. Most prominent of its efforts is the introduction of iodized salt in most countries for the prevention of goiter<ref name=Bunnell>Bunnell, J. E., R. B. Finkelman, J. A. Centeno, and O. Selinus, 2007, Medical Geology: a globally emerging discipline. Geologica Acta, 5(3), 273-281.</ref>

However, the above-mentioned issues are not the total range of medical geology. It is also interested in the use of geologic materials to cure various kinds of diseases. This has led to researches into the use of clay minerals for therapeutic purposes. It has also launched profound research into the use of mineralized thermal waters for the treatment of various diseases. These efforts have yielded laudable results over many decades. Most prominent of its efforts is the introduction of iodized salt in most countries for the prevention of goiter<ref name=Bunnell>Bunnell, J. E., R. B. Finkelman, J. A. Centeno, and O. Selinus, 2007, Medical geology: A globally emerging discipline: Geologica Acta, v. 5, no. 3, p. 273—281.</ref>

Medical geology achieves these goals through a coordinated effort by various professionals from geology, geography, biochemistry and medical sciences.

Medical geology achieves these goals through a coordinated effort by various professionals from geology, geography, biochemistry and medical sciences.

In essence, ''medical geology is a multidisciplinary field of study in geology which studies the health effects of geological materials and processes on humans and animals with both good and, possibly, hazardous results.'' 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." The goal of this field is to find the right balance and intake of elements/minerals in order to improve and maintain health<ref name=Fnklman2005>Finkelman, R. B., J. A. Centeno, and O. Selinus, 2005, The Emerging Medical and Geological Associations: Transactions of the American Clinical and Climatological Association, 116, 155-165.</ref>

In essence, ''medical geology is a multidisciplinary field of study in geology which studies the health effects of geological materials and processes on humans and animals with both good and, possibly, hazardous results.'' 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." The goal of this field is to find the right balance and intake of elements/minerals in order to improve and maintain health<ref name=Fnklman2005>Finkelman, R. B., J. A. Centeno, and O. Selinus, 2005, The emerging medical and geological associations: Transactions of the American Clinical and Climatological Association, v. 116, p. 155–165.</ref>

According to Finkelman et al,<ref name=Fnklman2005 /> the range and scope of medical geology include:

According to Finkelman et al,<ref name=Fnklman2005 /> the range and scope of medical geology include:

Due to the complexity of health problems arising from the geology, medical geology uses a multidisciplinary approach in its operations: it integrates experts from geology, geography, biochemistry and medical sciences who work as a team to tackle health problems ([[:File:UNN_Medical_Geology_Fig_1.png|Figure 1]]).

Due to the complexity of health problems arising from the geology, medical geology uses a multidisciplinary approach in its operations: it integrates experts from geology, geography, biochemistry and medical sciences who work as a team to tackle health problems ([[:File:UNN_Medical_Geology_Fig_1.png|Figure 1]]).

Geographical approaches are employed to ascertain the total number of individuals affected by an epidemic through the use of spatial analysis. On the other hand, biochemical studies provide an insight into the processes that elements undergo in biochemical systems while the burden of studying the epidemiological and toxicological aspects of diseases lies on the shoulders of medical sciences. Through such approaches, medical doctors are able to cure such diseases.<ref name=Setal2013>Selinus, O., B. Alloway, J. A. Centeno, R. B. Finkelman, R. Fuge, U. Lindh, and P. Smedley, (eds.) 2013. Essentials of Medical Geology. Elsevier, Amsterdam, 805p.</ref>

Geographical approaches are employed to ascertain the total number of individuals affected by an epidemic through the use of spatial analysis. On the other hand, biochemical studies provide an insight into the processes that elements undergo in biochemical systems while the burden of studying the epidemiological and toxicological aspects of diseases lies on the shoulders of medical sciences. Through such approaches, medical doctors are able to cure such diseases.<ref name=Setal2013>Selinus, O., B. Alloway, J. A. Centeno, R. B. Finkelman, R. Fuge, U. Lindh, and P. Smedley, eds., 2013. Essentials of medical geology: Amsterdam, Elsevier, 805 p.</ref>

Furthermore, geology is employed as a tool in identifying the causative element(s)/mineral(s) of the epidemic. This is achieved through desk study and field work aimed at identifying the host rock or soil and to map its lateral extent. Water sources such as lakes, rivers, streams and man- made wells are not left out in such studies. Mines, quarries and ore processing sites are all brought under the surveillance of geologists. This is achieved through a comprehensive mix of three aspects of geology: geochemistry, mineralogy and hydrogeology.

Furthermore, geology is employed as a tool in identifying the causative element(s) and mineral(s) of the epidemic. This is achieved through desk study and field work aimed at identifying the host rock or soil and to map its [[lateral]] extent. Water sources such as lakes, rivers, streams and man- made wells are not left out in such studies. Mines, quarries and ore processing sites are all brought under the surveillance of geologists. This is achieved through a comprehensive mix of three aspects of geology: geochemistry, mineralogy and hydrogeology.

Geochemistry is the study of the chemical changes in the earth. More specifically, it is the study of the absolute and relative abundances of chemical elements in minerals, soils, ores, rocks, water and atmosphere of the earth and the distribution of and movement of these elements from one place to another as a result of their chemical and physical characteristics. This approach is used extensively in the search for the causative element of a particular epidemic.

Geochemistry is the study of the chemical changes in the earth. More specifically, it is the study of the absolute and relative abundances of chemical elements in minerals, soils, ores, rocks, water and atmosphere of the earth and the distribution of and movement of these elements from one place to another as a result of their chemical and physical characteristics. This approach is used extensively in the search for the causative element of a particular epidemic.

Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure and optical properties of minerals.

Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure and optical properties of minerals.

Simply put, hydrogeology is the aspect of geology that studies the interaction between geologic materials and groundwater; because, as ground water passes through geologic media, it takes up some of the elements either in suspension or in solution. Consumption of such contaminated water sources can be ‘grave’. Thus, hydrogeology is important in gaining useful understanding of the water quality of a region/locality.

Simply put, hydrogeology is the aspect of geology that studies the interaction between geologic materials and groundwater; because, as ground water passes through geologic media, it takes up some of the elements either in suspension or in solution. Consumption of such contaminated water sources can be ‘grave’. Thus, hydrogeology is important in gaining useful understanding of the water quality of a region or locality.

===Environment and our health===

===Environment and our health===

[[File:UNN_Medical_Geology_Fig_2.png|thumb|400px|{{figure number|2}}Geologic cross-section of the Pikes Peak area showing the sources of fluoride in the Colorado Spring.<ref name=Fnklman2010b>Finkelman, R. B., H. Gingerich, J. A. Centeno, and G. Krieger, 2010b, Medical Geology Issues in North America, in O. Selinus, B. Alloway, J. A. Centeno, R. B. Finkelman, R. Fuge, U. Lindh, and P. Smedley, eds., Essentials of Medical Geology. Elsevier, Amsterdam, 1-9.</ref>]]

[[File:UNN_Medical_Geology_Fig_2.png|thumb|400px|{{figure number|2}}Geologic cross-section of the Pikes Peak area showing the sources of fluoride in the Colorado Spring.<ref name=Fnklman2010b>Finkelman, R. B., H. Gingerich, J. A. Centeno, and G. Krieger, 2010b, Medical geology Issues in North America, ''in'' O. Selinus, B. Alloway, J. A. Centeno, R. B. Finkelman, R. Fuge, U. Lindh, and P. Smedley, eds., Essentials of Medical Geology: Amsterdam, Elsevier, p. 1–9.</ref>]]

Over the years, it has been observed that the environment man lives in affects his health. For instance, the people of Maputaland, South Africa, are plagued by nutrient-poor soil. Maize grown in this region has very low content of elements such as calcium, potassium and phosphorous.<ref>Selinus, O. and A. Frank, 2000. Medical Geology. Environmental Medicine, Joint Industrial Safety Council, 333, 164-183.</ref> This is as a result of low concentration of these elements in the rocks of that region. Countries in southern Africa also suffer from selenium deficiency in their soils. This accounts for the spread of HIV-1 virus in this zone as selenium which inhibits the replication of HIV-1 is lacking in their soil. Still in Africa, Kerala Province in Uganda is another region under the “hammer” of geology. Children in this province suffer from a ‘grave’ coronary heart condition called endomyocardial fibrosis (EMF). This epidemic is attributed to the deliberate eating of soil containing the element cerium.<ref name=Dvies>Davies, T. C., 2010. Medical Geology in Africa, ''in'' O. Selinus, R. B. Finkelman, and J. A. Centeno, eds., Medical Geology: A Regional Synthesis, 199–216.</ref>

Over the years, it has been observed that the environment man lives in affects his health. For instance, the people of Maputaland, South Africa, are plagued by nutrient-poor soil. Maize grown in this region has very low content of elements such as calcium, potassium and phosphorous.<ref>Selinus, O. and A. Frank, 2000, Medical geology: Environmental medicine: Joint Industrial Safety Council, v. 333, p. 164–183.</ref> This is as a result of low concentration of these elements in the rocks of that region. Countries in southern Africa also suffer from selenium deficiency in their soils. This accounts for the spread of HIV-1 virus in this zone as selenium which inhibits the replication of HIV-1 is lacking in their soil. Still in Africa, Kerala Province in Uganda is another region under the “hammer” of geology. Children in this province suffer from a ‘grave’ coronary heart condition called endomyocardial fibrosis (EMF). This epidemic is attributed to the deliberate eating of soil containing the element cerium.<ref name=Dvies>Davies, T. C., 2010, Medical geology in Africa, ''in'' O. Selinus, R. B. Finkelman, and J. A. Centeno, eds., Medical Geology: A Regional Synthesis: Berlin, Springer, p. 199–216.</ref>

China is not left aside in these problems. The country suffers from deficiencies and excessiveness of selenium in many parts of the country resulting in life-threatening health problems. China also suffers from the influx of arsenic into coal deposits whose domestic use has resulted to untold chronic health effects over the years.<ref name=Skinner />

China is not left aside in these problems. The country suffers from deficiencies and excessiveness of selenium in many parts of the country resulting in life-threatening health problems. China also suffers from the influx of arsenic into [[coal]] deposits whose domestic use has resulted to untold chronic health effects over the years.<ref name=Skinner />

The use of water from the Colorado Springs at the Pikes Peak in the Rocky Mountain region of USA had led to dental fluorosis amongst children. This condition arose as a result of meteoric waters that flowed over faulted granitic batholiths.<ref name=Fnklman2010b /> The meteoric waters ‘picked up’ fluoride from easily dissolved minerals at the fault and incorporated it into the flow. Fluoride was also injected into the Colorado Springs by fluoride-enriched fractured and faulted Cretaceous Pierre Shale that underlies the spring ([[:File:UNN_Medical_Geology_Fig_2.png|Figure 2]]).

The use of water from the Colorado Springs at the Pikes Peak in the Rocky Mountain region of the United State had led to dental fluorosis amongst children. This condition arose as a result of meteoric waters that flowed over faulted granitic batholiths.<ref name=Fnklman2010b /> The meteoric waters ‘picked up’ fluoride from easily dissolved minerals at the fault and incorporated it into the flow. Fluoride was also injected into the Colorado Springs by fluoride-enriched fractured and faulted Cretaceous Pierre Shale that underlies the spring ([[:File:UNN_Medical_Geology_Fig_2.png|Figure 2]]).

===Biological classification of elements===

===Biological classification of elements===

Naturally occurring elements are classified into major elements, minor elements, trace elements and noble gases ([[:File:UNN_Medical_Geology_Fig_3.png|Figure 3]]).

Naturally occurring elements are classified into major elements, minor elements, trace elements and noble gases ([[:File:UNN_Medical_Geology_Fig_3.png|Figure 3]]).

According to Nordberg, and Cherian<ref>Nordberg, M. and M. G. Cherian, 2010. Biological Responses of Elements. In: Selinus, O., Alloway, B., Centeno, J.A., Finkelman, R.B., Fuge, R., Lindh, U. and Smedley, P. (eds.) Essentials of Medical Geology. Elsevier, Amsterdam, 179-200.</ref> major elements are those elements that are needed in large quantities in the body; each makes more than 1% of the human body (oxygen alone making up to 65% of the body). They include hydrogen, oxygen, carbon and nitrogen. These elements form most of the DNA structures in the human body; they occur in most organs and tissues. In addition, they are the main building blocks of enzymes; they are also important constituents of the cell membrane, inter-cellular, intracellular fluids and are actively involved in metabolic processes, all in their ionic states. Hence, in the event of high intake of these elements, the body has many ‘sites’ where they can be used. Nature provides a good abundance of these elements as it has been observed that the concentration of these elements is fairly the same in similar rocks and show the least variance compared to the minor and trace elements. Thus, they rarely pose problems.<ref name=Setal2013 />

According to Nordberg, and Cherian<ref>Nordberg, M. and M. G. Cherian, 2010, Biological responses of elements, ''in'' O. Selinus, B. Alloway, J. A. Centeno, R. B. Finkelman, R. Fuge, U. Lindh, and P. Smedley, P., eds., Essentials of medical geology: Amsterdam, Elsevier, p. 179–200.</ref> major elements are those elements that are needed in large quantities in the body; each makes more than 1% of the human body (oxygen alone making up to 65% of the body). They include hydrogen, oxygen, carbon and nitrogen. These elements form most of the DNA structures in the human body; they occur in most organs and tissues. In addition, they are the main building blocks of enzymes; they are also important constituents of the cell membrane, inter-cellular, intracellular fluids and are actively involved in metabolic processes, all in their ionic states. Hence, in the event of high intake of these elements, the body has many ‘sites’ where they can be used. Nature provides a good abundance of these elements as it has been observed that the concentration of these elements is fairly the same in similar rocks and show the least variance compared to the minor and trace elements. Thus, they rarely pose problems.<ref name=Setal2013 />

Minor elements are those elements that are needed in moderate quantities; each has a concentration of 0.1% to 1.0% in the body.<ref name=Setal2013 /> They share in the functions of the major elements, but in smaller amounts.

Minor elements are those elements that are needed in moderate quantities; each has a concentration of 0.1% to 1.0% in the body.<ref name=Setal2013 /> They share in the functions of the major elements, but in smaller amounts.

Trace elements are those elements that have concentrations far below 0.1% in the body; they are needed in the body only in parts per million (ppm). They are essential to plant and animal lives only in trace amounts. Such trace elements are called essential trace elements.<ref>Christine, L. E., G. Sujuan, L. Yiming, L. Chaoke, J. Rongdi, S. H. Kathleen, C. Jingxiang, M. Feng, W. Yunpeng, Y. Po, S. Shuzhuang, W. U. Frederick, W. S. Charles, and C. H. Hugh, 2000, Trace Element Levels in Drinking Water and Cognitive Function among Elderly Chinese: American Journal of Epidemiology, 151(9), 913-920.</ref> They are highly variable in their abundance in various rocks (Table 1).

Trace elements are those elements that have concentrations far below 0.1% in the body; they are needed in the body only in parts per million (ppm). They are essential to plant and animal lives only in trace amounts. Such trace elements are called essential trace elements.<ref>Christine, L. E., G. Sujuan, L. Yiming, L. Chaoke, J. Rongdi, S. H. Kathleen, C. Jingxiang, M. Feng, W. Yunpeng, Y. Po, S. Shuzhuang, W. U. Frederick, W. S. Charles, and C. H. Hugh, 2000, Trace element levels in drinking water and cognitive function among elderly Chinese: American Journal of Epidemiology, v. 151, no. 9, p. 913–920.</ref> They are highly variable in their abundance in various rocks (Table 1).

{| class="wikitable"

{| class="wikitable"

|-

|-

|+ Table 1: Average abundances of selected elements in bedrock, all values in ppm.<ref name=Khndare>Khandare, H. W., 2012, Medical Geology: An Emerging Field of Interdisciplinary Research on Geology and Human Health. International Journal of ChemTech Research CODEN (USA), 4(4), 1792-1796.</ref>

|+ {{table number|1}}Average abundances of selected elements in bedrock, all values in ppm.<ref name=Khndare>Khandare, H. W., 2012, Medical geology: An emerging field of interdisciplinary research on geology and human health: International Journal of ChemTech Research CODEN (USA), v. 4, no. 4, p. 1792–1796.</ref>

|-

|-

! Element !! Ultrabasic Rock !! Basalt !! Granite !! Shale !! Limestone

! Element !! Ultrabasic Rock !! Basalt !! Granite !! Shale !! Limestone

{| class="wikitable"

{| class="wikitable"

|-

|-

|+ Table 2: Diseases caused by the deficiencies and excessiveness/toxicity of some trace elements.<ref name=Khndare />

|+ {{table number|2}}Diseases caused by the deficiencies and excessiveness/toxicity of some trace elements.<ref name=Khndare />

|-

|-

! Element || Deficiency || Excessiveness/Toxicity

! Element || Deficiency || Excessiveness/Toxicity

However, some trace elements such as As, Cd, Pb, Hg and Rn have no/limited biological functions and are generally toxic to humans; they are called non-essential trace elements.<ref name=Setal2013 />

However, some trace elements such as As, Cd, Pb, Hg and Rn have no/limited biological functions and are generally toxic to humans; they are called non-essential trace elements.<ref name=Setal2013 />

From the above biological classification of elements, it can be seen why medical geology sets its eyes on the trace elements: they are the causes of most health problems sourced from geologic materials. They emanate from igneous, sedimentary or metamorphic rocks, as well as industrial minerals. They contaminate groundwater through boreholes or through springs/streams. In addition, they can be released during volcanic eruptions.

From the above biological classification of elements, it can be seen why medical geology sets its eyes on the trace elements: they are the causes of most health problems sourced from geologic materials. They emanate from [[igneous]], sedimentary or metamorphic rocks, as well as industrial minerals. They contaminate groundwater through boreholes or through springs or streams. In addition, they can be released during volcanic eruptions.

===Geochemobiological Pathways===

===Geochemobiological Pathways===

Elements are released from rocks through weathering− the process by which rocks are broken down into smaller components.

Elements are released from rocks through weathering− the process by which rocks are broken down into smaller components.

Physical weathering is the process by which rocks are broken down into smaller chunks without altering its mineral content. It occurs through temperature changes and by the action of the wind. Temperature variation leads to the development of flakes on the rocks whose removal exposes subsequent layers to further heating and cooling and, then, to chemical weathering. Physical disintegration of rocks is also caused by the action of burrowing animals and plant roots. Freezing of water in crevices of rocks is another force that disintegrates rocks making them prone to chemical weathering.<ref name=Setal2010>Selinus, O., R. B. Finkelman, and J. Centeno, (Eds), 2010. Medical Geology – A Regional Synthesis. Springer, Germany, 392p.</ref>

Physical weathering is the process by which rocks are broken down into smaller chunks without altering its mineral content. It occurs through temperature changes and by the action of the wind. Temperature variation leads to the development of flakes on the rocks whose removal exposes subsequent layers to further heating and cooling and, then, to chemical weathering. Physical disintegration of rocks is also caused by the action of burrowing animals and plant roots. Freezing of water in crevices of rocks is another force that disintegrates rocks making them prone to chemical weathering.<ref name=Setal2010>Selinus, O., R. B. Finkelman, and J. Centeno, eds., 2010, Medical geology—A regional synthesis: Berlin, Springer, 392 p.</ref>

Chemical weathering describes the process that alters the chemistry of minerals. It can proceed through hydration, hydrolysis, oxidation, reduction and dissolution. Chemical weathering is fuelled by water and weak soil acids.<ref name=Setal2013 />

Chemical weathering describes the process that alters the chemistry of minerals. It can proceed through hydration, hydrolysis, oxidation, reduction and dissolution. Chemical weathering is fuelled by water and weak soil acids.<ref name=Setal2013 />

In addition to these, there are processes that make the various elements available to plants: sorption and desorption. According to Selinus et al,<ref name=Setal2013 /> sorption is the retention of metal ions on the surfaces of soil particles through mutual attraction between oppositely charged particles. Desorption refers to the release of these metal ions for plant use as a result of alterations in pH and redox conditions. By consuming plants and animals raised on such soils, man comes in contact with the elements originally in the rocks.

In addition to these, there are processes that make the various elements available to plants: sorption and desorption. According to Selinus et al.,<ref name=Setal2013 /> sorption is the retention of metal ions on the surfaces of soil particles through mutual attraction between oppositely charged particles. Desorption refers to the release of these metal ions for plant use as a result of alterations in pH and redox conditions. By consuming plants and animals raised on such soils, man comes in contact with the elements originally in the rocks.

Another pathway through which humans come in contact with the earth’s elements is by water intake whether from man-made wells, rivers, streams or lakes.<ref name=Skinner /> These emanate from groundwater which might have leached both toxic and non-toxic elements from rocks through which it flowed.

Another pathway through which humans come in contact with the earth’s elements is by water intake whether from man-made wells, rivers, streams or lakes.<ref name=Skinner /> These emanate from groundwater which might have leached both toxic and non-toxic elements from rocks through which it flowed.

Inhalation of volcanic gases and dust from deserts, un-tarred roads, mines and volcanic emanations form another important pathway of exposure to dangerous elements. Volcanism is the principal process that brings elements to the surface from deep within the earth. The volcanic eruption of Mount Pinatubo is a splendid example of the dramatic effects of geology. During just two days in June ,1991, Mount Pinatubo, Philippines ejected 10 billion metric tonnes of magma and 20 million tonnes of SO2 for over 15,000 meters high into the atmosphere; the resulting aerosols influenced global climate for three years. This single event introduced an estimated 800,000 tonnes of zinc, 600,000 tonnes of copper, 550,000 tonnes of chromium, 100,000 tonnes of lead, 1000 tonnes of cadmium, 10,000 tonnes of arsenic, 800 tonnes of mercury, and 30,000 tonnes of nickel to the surface environment (Garrett, 2000).

Inhalation of volcanic gases and dust from deserts, un-tarred roads, mines and volcanic emanations form another important pathway of exposure to dangerous elements. Volcanism is the principal process that brings elements to the surface from deep within the earth. The volcanic eruption of Mount Pinatubo is a splendid example of the dramatic effects of geology. During just two days in June 1991, Mount Pinatubo, Philippines, ejected 10 billion metric tonnes of magma and 20 million tonnes of SO2 for over 15,000 meters high into the atmosphere; the resulting aerosols influenced global climate for three years. This single event introduced an estimated 800,000 tonnes of zinc, 600,000 tonnes of copper, 550,000 tonnes of chromium, 100,000 tonnes of lead, 1000 tonnes of cadmium, 10,000 tonnes of arsenic, 800 tonnes of mercury, and 30,000 tonnes of nickel to the surface environment.<ref>Garrett, R. G., 2000, Natural distribution and abundance of elements, ''in'' O. Selinus, ed., Essentials of medical geology: Berlin, Springer, p. 35–57</ref>

==Health issues arising from selected elements and geological materials and processes==

==Health issues arising from selected elements and geological materials and processes==

===Excessiveness of Arsenic (As)===

===Excessiveness of Arsenic (As)===

'''Geochemistry of Arsenic:''' Arsenic is a metalloid and has high affinity for sulphide-bearing minerals. One of such minerals is pyrite, hence the formation of arsenopyrite (FeAsS). In the tropics, oxidative weathering leads to the formation Arsenite (As3+) and Arsenate (As4+).<ref name=Adeyinka>Adeyinka, O., N. M. Miranda, P. T. Raymond, Y. Abubakar, and C. A. Edafetano, 2013, Arsenic in Rocks of Kaltungo Area, Upper Benue Trough, Nigeria. Earth Resources, 1(1), 5-11.</ref>

'''Geochemistry of Arsenic:''' Arsenic is a metalloid and has high affinity for sulphide-bearing minerals. One of such minerals is pyrite, hence the formation of arsenopyrite (FeAsS). In the tropics, oxidative weathering leads to the formation Arsenite (As3+) and Arsenate (As4+).<ref name=Adeyinka>Adeyinka, O., N. M. Miranda, P. T. Raymond, Y. Abubakar, and C. A. Edafetano, 2013, Arsenic in rocks of Kaltungo Area, Upper Benue Trough, Nigeria: Earth Resources, v. 1, no. 1, p. 5–11.</ref>

'''Mechanism of Toxicity:''' Due to its affinity for sulphur, arsenic in biological systems, attacks sulphur-bearing enzymes by binding and blocking them. Soon, it makes its way through the digestive tract to the liver, spleen and lungs. Although most arsenic is excreted, some are still retained in the skin, hair, legs, nails and teeth.<ref name=Fnklman2010a>Finkelman, R. B., H. E. Belkin, and B. Zheng, 2010a, Health Impacts of Domestic Coal Use in China: Proceedings National Academy of Science, (USA), 96, 3427-3431.</ref> As the concentration increases, adverse health effects result leading to carcinogenic or non-cancer problems. Prolonged exposure to arsenic induces peripheral arteriosclerosis, hair fall-out, retarded nail growth and various types of skin conditions such as hyperkeratosis, hyper- pigmentation and skin malignancies. These levels of disorders are prominent in places with arsenic concentrations of 100−1000μg/l in their groundwater as against 50μg/l stipulated by WHO in 1993.<ref name=Htton>Hutton, M., 1987, Human Health Concerns of Lead, Mercury, Cadmium and Arsenic. John Wiley & Sons Ltd, Uk, 68p.</ref> However, the presence of selenium reduces the toxic effects of arsenic.

'''Mechanism of Toxicity:''' Due to its affinity for sulphur, arsenic in biological systems, attacks sulphur-bearing enzymes by binding and blocking them. Soon, it makes its way through the digestive tract to the liver, spleen and lungs. Although most arsenic is excreted, some are still retained in the skin, hair, legs, nails and teeth.<ref name=Fnklman2010a>Finkelman, R. B., H. E. Belkin, and B. Zheng, 2010a, Health Impacts of Domestic Coal Use in China: Proceedings National Academy of Science, (USA), 96, 3427-3431.</ref> As the concentration increases, adverse health effects result leading to carcinogenic or non-cancer problems. Prolonged exposure to arsenic induces peripheral arteriosclerosis, hair fall-out, retarded nail growth and various types of skin conditions such as hyperkeratosis, hyper- pigmentation and skin malignancies. These levels of disorders are prominent in places with arsenic concentrations of 100−1000μg/l in their groundwater as against 50μg/l stipulated by WHO in 1993.<ref name=Htton>Hutton, M., 1987, Human Health Concerns of Lead, Mercury, Cadmium and Arsenic. John Wiley & Sons Ltd, Uk, 68p.</ref> However, the presence of selenium reduces the toxic effects of arsenic.

Arsenic, in this area, is released into the groundwater and surface water through dissolution, weathering and erosion of the host rocks. Being an anion, it sticks to mineral surfaces especially iron from biotite.<ref name=Adeyinka /> This explains the mobility of iron and arsenic during weathering and deposition in the area.

Arsenic, in this area, is released into the groundwater and surface water through dissolution, weathering and erosion of the host rocks. Being an anion, it sticks to mineral surfaces especially iron from biotite.<ref name=Adeyinka /> This explains the mobility of iron and arsenic during weathering and deposition in the area.

Results show that the concentration of arsenic in all the rock types at Kaltungo and the environs is far above the average crustal abundance of 2 ppm. Generally, the concentration ranges from 152.900 ppm to 235.200 ppm in the coarse porphyritic granite; it varies from 232.200 ppm to 243.100 ppm in the biotite granite. In the Bima Sandstone, the concentration ranges from 228.700 ppm to 87.540 ppm while in the basalts of the area, the range is from 174.600 ppm to 151.600 ppm.<ref name=Adeyinka />

Results show that the concentration of arsenic in all the rock types at Kaltungo and the environs is far above the average [[crust]]al abundance of 2 ppm. Generally, the concentration ranges from 152,900 ppm to 235,200 ppm in the coarse porphyritic granite; it varies from 232,200 ppm to 243,100 ppm in the biotite granite. In the Bima Sandstone, the concentration ranges from 228,700 ppm to 87,540 ppm while in the basalts of the area, the range is from 174,600 ppm to 151,600 ppm.<ref name=Adeyinka />

====Health impacts of excessive arsenic in groundwater in Zimbabwe====

====Health impacts of excessive arsenic in groundwater in Zimbabwe====

====Arsenosis in China====

====Arsenosis in China====

[[File:UNN_Medical_Geology_Fig_5.png|thumb|400px|{{figure number|5}}Hyperkeratosis/Ulceration of the Foot and Hands and Hair Fall-Out (Wuyi et al, 2003).]]

[[File:UNN_Medical_Geology_Fig_5.png|thumb|400px|{{figure number|5}}Hyperkeratosis/Ulceration of the Foot and Hands and Hair Fall-Out.<ref name=Wuyi>Wuyi, W., Y. Linsheng, H. Shaofan, and T. Jian’an, 2003, Mitigation of endemic Arsenocosis with Selenium: an example from China: HCWSkinner ARBerger, p. 51–56.</ref>]]

Arsenosis refers to a range of adverse health effects caused by the intake of arsenic into the body system above the recommended values of 50μg/l.

Arsenosis refers to a range of adverse health effects caused by the intake of arsenic into the body system above the recommended values of 50μg/l.

In Guizhou Province, China, the cool, damp autumn weather forces villagers to bring their harvest of chili peppers and corn indoors to dry. They hang the peppers over unvented stoves which were formally fueled by wood. But, due to the destruction of forests, wood became scarce; so, the villagers turned to the plentiful outcrops of coal for heating, cooking and drying their harvests.<ref name=Fnklman2010a /> Unknowingly to them, mineralizing solutions in this area had deposited enormous concentrations of arsenic − up to 35,000 ppm − and other trace elements on the coals. It should be noted that normal coals have arsenic concentration of 20 ppm. Consumption of the chili peppers dried over these arsenic-rich coals exposed the natives to arsenosis. The dried chili peppers contained up to 500 ppm of arsenic whereas normal chili peppers contain less than 1 ppm of arsenic (Wuyi et al, 2003). In addition, inhalation of arsenic-laden indoor air derived from coal combustion has increased the toll of arsenic poisoning in the region.<ref name=Fnklman2005 />

In Guizhou Province, China, the cool, damp autumn weather forces villagers to bring their harvest of chili peppers and corn indoors to dry. They hang the peppers over unvented stoves which were formally fueled by wood. But, due to the destruction of forests, wood became scarce; so, the villagers turned to the plentiful outcrops of [[coal]] for heating, cooking and drying their harvests.<ref name=Fnklman2010a /> Unknowingly to them, mineralizing solutions in this area had deposited enormous concentrations of arsenic—up to 35,000 ppm—and other trace elements on the coals. It should be noted that normal coals have arsenic concentration of 20 ppm. Consumption of the chili peppers dried over these arsenic-rich coals exposed the natives to arsenosis. The dried chili peppers contained up to 500 ppm of arsenic whereas normal chili peppers contain less than 1 ppm of arsenic.<ref name=Wuyi /> In addition, inhalation of arsenic-laden indoor air derived from coal combustion has increased the toll of arsenic poisoning in the region.<ref name=Fnklman2005 />

Chemical and mineralogical tests conducted showed that there were many arsenic-bearing minerals in the coals, although, much of the arsenic is bound to the organic matrix of the coals. This observation presented two problems namely: (1) since arsenic is bound to the organic matrix, conventional reduction methods of removing arsenic was ineffective; (2) the visually observable pyrite on the coal samples was not reliable in establishing arsenic-rich samples.

Chemical and mineralogical tests conducted showed that there were many arsenic-bearing minerals in the coals, although, much of the arsenic is bound to the organic matrix of the coals. This observation presented two problems namely: (1) since arsenic is bound to the organic matrix, conventional reduction methods of removing arsenic was ineffective; (2) the visually observable pyrite on the coal samples was not reliable in establishing arsenic-rich samples.

{| class="wikitable"

{| class="wikitable"

|-

|-

|+ Table 3: Effects of Arsenic at various organs.<ref name=Htton />

|+ {{table number|3}}Effects of Arsenic at various organs.<ref name=Htton />

|-

|-

! Organ Affected || Effects

! Organ Affected || Effects

To help solve this problem, villagers were supplied with field test kits to ascertain the arsenic content of coals in the field before use in their unvented stoves. Thus, chili peppers dried over the unvented stoves were free from arsenic contamination.

To help solve this problem, villagers were supplied with field test kits to ascertain the arsenic content of coals in the field before use in their unvented stoves. Thus, chili peppers dried over the unvented stoves were free from arsenic contamination.

Arsenosis is also reported in Inner Mongolia Autonomous Region of China. It is caused by the contamination of surface and groundwater resources by arsenic derived from high- arsenic minerals. Chifeng City in Kosk Teng County in eastern Inner Mongolia is the most affected in this region. It is located on the slope of a mountain with arsenopyrite deposits. The weathering of arsenopyrite (FeAsS) deposits releases arsenic into the groundwater and surface water bodies. The groundwater was delivered to the surface through springs and wells. Out of 34 wells investigated, arsenic concentration between 0.16 mg/l to 0.45 mg/l was observed by Selinus et al.<ref name=Setal2010 /> 22 persons out of 45 persons tested positive to minor arsenosis.<ref name=Setal2010 />

Arsenosis is also reported in Inner Mongolia Autonomous Region of China. It is caused by the contamination of surface and groundwater resources by arsenic derived from high-arsenic minerals. Chifeng City in Kosk Teng County in eastern Inner Mongolia is the most affected in this region. It is located on the slope of a mountain with arsenopyrite deposits. The weathering of arsenopyrite (FeAsS) deposits releases arsenic into the groundwater and surface water bodies. The groundwater was delivered to the surface through springs and wells. Out of 34 wells investigated, arsenic concentration between 0.16 mg/l to 0.45 mg/l was observed by Selinus et al.<ref name=Setal2010 /> 22 persons out of 45 persons tested positive to minor arsenosis.<ref name=Setal2010 />

====Water purification technologies to remove arsenic from water====

====Water purification technologies to remove arsenic from water====

===Iodine Deficiency Disorders (IDD)===

===Iodine Deficiency Disorders (IDD)===

[[File:UNN_Medical_Geology_Fig_6.png|thumb|400px|{{figure number|6}}Man with goiter<ref>Fuge, R., 2010, Soils and Iodine Deficiency. In: Selinus, O., Alloway, B., Centeno, J.A., Finkelman, R.B., Fuge, R., Lindh, U. and Smedley, P., eds., Essentials of Medical Geology. Elsevier, Amsterdam: 417-433.</ref>]]

[[File:UNN_Medical_Geology_Fig_6.png|thumb|400px|{{figure number|6}}Man with goiter<ref>Fuge, R., 2010, Soils and iodine deficiency, ''in'' O. Selinus, B. Alloway, J. A. Centeno, R. B. Finkelman, R. Fuge, U. Lindh, and P. Smedley, eds., Essentials of medical geology: Amsterdam, Elsevier, p. 417-433.</ref>]]

Iodine is very important for the proper functioning of the human body. In all mammals, it is needed for the efficient functioning of the adult in trace amounts in the order of 0.0004 wt%.<ref name=Dvies /> This quantity is maintained as a result of small intake of iodine from drinking water and various forms of foodstuffs throughout the lifetime of the mammal.

Iodine is very important for the proper functioning of the human body. In all mammals, it is needed for the efficient functioning of the adult in trace amounts in the order of 0.0004 wt%.<ref name=Dvies /> This quantity is maintained as a result of small intake of iodine from drinking water and various forms of foodstuffs throughout the lifetime of the mammal.

To curtail IDD, salt iodization programme has been introduced, not only in this region but in all African countries. However, this project has not yielded maximum results due to the counteracting effect of goitrogens in the African diet. Goitrogenic effect comes from certain vegetables such as brassica. It proceeds by depressing the formation of thyroid hormone leading to increased secretion of thyroid stimulating hormone (TSH). The thyroid gland responds to this by enlarging itself as a compensating mechanism leading to the development of goiter ([[:File:UNN_Medical_Geology_Fig_6.png|Figure 6]]).<ref name=Dvies /> Another substance with goitrogenous effect is thiocyanate which is present in cassava consumed in many African countries. It inhibits the entrance of iodine into the thyroid gland.<ref name=Dvies />

To curtail IDD, salt iodization programme has been introduced, not only in this region but in all African countries. However, this project has not yielded maximum results due to the counteracting effect of goitrogens in the African diet. Goitrogenic effect comes from certain vegetables such as brassica. It proceeds by depressing the formation of thyroid hormone leading to increased secretion of thyroid stimulating hormone (TSH). The thyroid gland responds to this by enlarging itself as a compensating mechanism leading to the development of goiter ([[:File:UNN_Medical_Geology_Fig_6.png|Figure 6]]).<ref name=Dvies /> Another substance with goitrogenous effect is thiocyanate which is present in cassava consumed in many African countries. It inhibits the entrance of iodine into the thyroid gland.<ref name=Dvies />

In China, about 425 million people are at risk of IDD. In iodine deficiency areas, a serious shortage of iodine intake by pregnant women would affect the development of the nervous system of the fetus and newborn infants would likely suffer from cretinism and related health problems (Zheng et al, 2010). Endemic cretinism prevailed in Chinese regions with acute iodine shortage. Analysis showed that places with iodine threshold of 25μg suffer from endemic cretinism whereas places with only goiter usually have iodine threshold of 50 μg. This triggered off a research into the relationship between goiter and cretinism in 25 provinces on 750,000 persons. The research showed that goiter had an average prevalence rate of 24.92% while cretinism had an average prevalence rate of 3.15% (Zheng et al, 2010). Fortunately, inhalation of iodine volatized from coal has contributed to increased reduction in the goiter cases.

In China, about 425 million people are at risk of IDD. In iodine deficiency areas, a serious shortage of iodine intake by pregnant women would affect the development of the nervous system of the fetus and newborn infants would likely suffer from cretinism and related health problems.<ref name=Zheng2010>Zheng, B., B. Wang, and R. B. Finkelman, 2010, Medical geology in China: Then and now, ''in'' O. Selinus, R. B. Finkelman, and J. A. Centeno, eds., Medical geology: A regional synthesis, p. 303–319.</ref> Endemic cretinism prevailed in Chinese regions with acute iodine shortage. Analysis showed that places with iodine threshold of 25μg suffer from endemic cretinism whereas places with only goiter usually have iodine threshold of 50 μg. This triggered off a research into the relationship between goiter and cretinism in 25 provinces on 750,000 persons. The research showed that goiter had an average prevalence rate of 24.92% while cretinism had an average prevalence rate of 3.15%.<ref name=Zheng2010 /> Fortunately, inhalation of iodine volatized from coal has contributed to increased reduction in the goiter cases.

===Health effects resulting from the deficiency and excessiveness of selenium===

===Health effects resulting from the deficiency and excessiveness of selenium===

According to Fordyce,<ref name=Fordyce>Fordyce, F., 2010, Selenium Deficiency and Toxicity in the Environment. In: Selinus, O., Alloway, B., Centeno, J.A., Finkelman, R.B., Fuge, R., Lindh, U. and Smedley, P., (eds.) 2010. Essentials of Medical Geology. Elsevier, Amsterdam, 375-413.</ref> selenium is found in phosphatic rocks, coals, organic-rich shales and sulphide mineralization. It occurs in the soil in the form of selenites (Se4+), selenates (Se6+), selenides (Se2-) and elemental selenium (Se0).

According to Fordyce,<ref name=Fordyce>Fordyce, F., 2010, Selenium deficiency and toxicity in the environment, ''in'' O. Selinus, B. Alloway, J. A. Centeno, R. B. Finkelman, R. Fuge, U. Lindh, and P. Smedley, eds., 2010, Essentials of medical geology: Amsterdam, Elsevier, p. 375–413.</ref> selenium is found in phosphatic rocks, coals, organic-rich shales and sulphide mineralization. It occurs in the soil in the form of selenites (Se4+), selenates (Se6+), selenides (Se2-) and elemental selenium (Se0).

It can accumulate in the kidneys, liver, marrow, myocardium, pancreas, lungs, skin and hair. <ref name=Fordyce />

It can accumulate in the kidneys, liver, marrow, myocardium, pancreas, lungs, skin and hair. <ref name=Fordyce />

[[File:UNN_Medical_Geology_Fig_7.png|thumb|400px|{{figure number|7}}(A) Rickets (skeletal fluorosis) in a three year old child; (B) Dental fluorosis.<ref name=Setal2010 />]]

[[File:UNN_Medical_Geology_Fig_7.png|thumb|400px|{{figure number|7}}(A) Rickets (skeletal fluorosis) in a three year old child; (B) Dental fluorosis.<ref name=Setal2010 />]]

With an electronegative value of 4.0, fluorine is the most reactive element on earth. It has very low dissociation energy. This means that it has the tendency to accept electrons from other elements, and has the greatest ease to form strong bonds. The fluoride ion has an ionic radius of 1.33 Ȧ and an ionic charge of -1; this is similar to that of the hydroxyl ion which has ionic charge of -1 and ionic radius of 1.32 Ȧ<ref name=Schmschula>Schamschula, R. C. and D. E. Barmes, 1981. Fluoride and health: Dental Caries, Osteoporosis and Cardiovascular Disease. Annual Review of Nutrient, 1, 427–35.</ref>

With an electronegative value of 4.0, fluorine is the most reactive element on earth. It has very low dissociation energy. This means that it has the tendency to accept electrons from other elements, and has the greatest ease to form strong bonds. The fluoride ion has an ionic radius of 1.33 Ȧ and an ionic charge of -1; this is similar to that of the hydroxyl ion which has ionic charge of -1 and ionic radius of 1.32 Ȧ<ref name=Schmschula>Schamschula, R. C. and D. E. Barmes, 1981, Fluoride and health: Dental caries, osteoporosis and cardiovascular disease: Annual Review of Nutrient, v. 1, p. 427–35.</ref>

Fluoride (F-), the ionic form of fluorine, can stimulate bone formation and it also has been demonstrated to reduce dental caries at doses of at least 0.7 mg/l in drinking water.<ref name=Setal2013 /> Concentration in the excess of this figure leads to adverse health effects called fluorosis (Table 4). Dental fluorosis occurs when the fluoride ions continually substitute for hydroxyl ions in the apatite [Ca10 (PO4)6(OH, F, Cl, Br)2] crystals of the enamel. The enamel loses its glittering appearance as chalky white patches develop; this is called mottled enamel.<ref name=Schmschula /> Dental fluorosis proceeds to change the colour of the teeth from chalky white to yellow, brown or black. Finally, the yellow, brown or black patches become dissolved ([[:File:UNN_Medical_Geology_Fig_7.png|Figure 7]]).

Fluoride (F-), the ionic form of fluorine, can stimulate bone formation and it also has been demonstrated to reduce dental caries at doses of at least 0.7 mg/l in drinking water.<ref name=Setal2013 /> Concentration in the excess of this figure leads to adverse health effects called fluorosis (Table 4). Dental fluorosis occurs when the fluoride ions continually substitute for hydroxyl ions in the apatite [Ca10 (PO4)6(OH, F, Cl, Br)2] crystals of the enamel. The enamel loses its glittering appearance as chalky white patches develop; this is called mottled enamel.<ref name=Schmschula /> Dental fluorosis proceeds to change the colour of the teeth from chalky white to yellow, brown or black. Finally, the yellow, brown or black patches become dissolved ([[:File:UNN_Medical_Geology_Fig_7.png|Figure 7]]).

{| class="wikitable"

{| class="wikitable"

|-

|-

|+ Table 4: Possible Health Effects of Different Fluoride Concentrations in Drinking Water.<ref name=Dvies />

|+ {{table number|4}}Possible Health Effects of Different Fluoride Concentrations in Drinking Water.<ref name=Dvies />

|-

|-

! Concentration of Fluoride (mg/l) || Possible Health Effects

! Concentration of Fluoride (mg/l) || Possible Health Effects

Geologic materials that are characteristically rich in fluorine are organic clays and shales, carbonatites, phosphates, hydrothermal ores and silicic igneous rocks such as rhyolites, dacites and granites.<ref name=Setal2010 />

Geologic materials that are characteristically rich in fluorine are organic clays and shales, carbonatites, phosphates, hydrothermal ores and silicic igneous rocks such as rhyolites, dacites and granites.<ref name=Setal2010 />

Studies have shown that fluoride mineralization occurs in tectonically unstable areas such as zones of rifting and zones characterized by rise of fluoride from the lower crust or upper mantle. This explains why people living in the African Rift zones and volcanic areas have high concentration of fluoride in their natural water bodies. In the East African Rift, in particular, most of the lakes are contaminated by fluoride as a result of influx of fluoride from hot springs and volcanic gases.<ref name=Dvies /> The lake with the highest fluoride concentration occurs in this area−Lake Nakuru in the Kenyan Rift Valley. According to Davies,<ref name=Dvies /> the water of this lake has fluoride concentration in the order of 2800 mg/l. Other African countries with high fluoride concentration in groundwater include granitic areas in Ghana and parts of Malawi and Tanzania while sedimentary areas with high fluoride concentration are found in parts of North Africa and Senegal in West Africa.<ref name=Dvies /> Nigeria, Zimbabwe and Ethiopia had been hit by adverse health conditions triggered by nutritional fluoride imbalance.<ref name=Dvies />

Studies have shown that fluoride mineralization occurs in tectonically unstable areas such as zones of rifting and zones characterized by rise of fluoride from the lower [[crust]] or upper [[mantle]]. This explains why people living in the African Rift zones and volcanic areas have high concentration of fluoride in their natural water bodies. In the East African Rift, in particular, most of the lakes are contaminated by fluoride as a result of influx of fluoride from hot springs and volcanic gases.<ref name=Dvies /> The lake with the highest fluoride concentration occurs in this area−Lake Nakuru in the Kenyan Rift Valley. According to Davies,<ref name=Dvies /> the water of this lake has fluoride concentration in the order of 2800 mg/l. Other African countries with high fluoride concentration in groundwater include granitic areas in Ghana and parts of Malawi and Tanzania while sedimentary areas with high fluoride concentration are found in parts of North Africa and Senegal in West Africa.<ref name=Dvies /> Nigeria, Zimbabwe and Ethiopia had been hit by adverse health conditions triggered by nutritional fluoride imbalance.<ref name=Dvies />

===Health effects of Cadmium, Cd===

===Health effects of Cadmium, Cd===

<gallery mode=packed heights=300px widths=300px>

<gallery mode=packed heights=300px widths=300px>

UNN_Medical_Geology_Fig_8.png|{{figure number|8}}Distribution of Cadmium in the central districts of Jamaica (after Wright et al, 2010).

UNN_Medical_Geology_Fig_8.png|{{figure number|8}}Distribution of Cadmium in the central districts of Jamaica<ref name=Wright>Wright, P. R. D., R. Rattray, and G. Lalor, 2010, A regional perspective of medical geology—Cadmium in Jamaica, ''in'' O. Selinus, R. B. Finkelman, and J. A. Centeno, eds., Medical geology: A regional synthesis: Berlin, Springer, p. 36–45.</ref>

UNN_Medical_Geology_Fig_9.png|{{figure number|9}}Correlation between yam Cd concentration and soil Cd concentration (Wright et al, 2010).

UNN_Medical_Geology_Fig_9.png|{{figure number|9}}Correlation between yam Cd concentration and soil Cd concentration.<ref name=Wright />

</gallery>

</gallery>

Cadmium has great affinity for sulphides and is therefore associated with sulphide deposits. It has very similar tetrahedral covalent radius to that of zinc; thus, it can displace zinc from sphalerite (ZnS).

Cadmium has great affinity for sulphides and is therefore associated with sulphide deposits. It has very similar tetrahedral covalent radius to that of zinc; thus, it can displace zinc from sphalerite (ZnS).

Cadmium is highly toxic to humans. According to Hutton,<ref name=Htton /> it mainly accumulates in soft tissues such as the kidneys and liver. In Japan, it is the cause of a disease known as itai-itai–a disease that affects mainly women.<ref name=Hisashi>Hisashi, N., F. Kunio, and K. Takashi, 2010, Medical Geology in China. In: Selinus, O., Finkelman, R.B. and Centeno, J.A., eds, Medical Geology: A Regional Synthesis, 329–338.</ref> Its symptoms include: backaches, pain in the limbs, arthralgia and pain in the pubic bones. This is the direct result of the loss of calcium in bones. The loss makes the bones to be fragile and causes the development of fractures. The victim remains in pain until death. In a particular autopsy conducted, 72 fracture points were seen.<ref name=Hisashi />

Cadmium is highly toxic to humans. According to Hutton,<ref name=Htton /> it mainly accumulates in soft tissues such as the kidneys and liver. In Japan, it is the cause of a disease known as itai-itai–a disease that affects mainly women.<ref name=Hisashi>Hisashi, N., F. Kunio, and K. Takashi, 2010, Medical geology in China, ''in'' O. Selinus, R. B. Finkelman, and J. A. Centeno, eds., Medical geology: A regional synthesis: Berlin, Springer, p. 329–338.</ref> Its symptoms include: backaches, pain in the limbs, arthralgia and pain in the pubic bones. This is the direct result of the loss of calcium in bones. The loss makes the bones to be fragile and causes the development of fractures. The victim remains in pain until death. In a particular autopsy conducted, 72 fracture points were seen.<ref name=Hisashi />

Health issues arising from high cadmium concentration has also been established in the central parts of Jamaica ([[:File:UNN_Medical_Geology_Fig_8.png|Figure 8]]). It occurs in the soil of a region with limestone and an overlying aluminum-rich bauxite deposit (Wright et al, 2010). Cadmium exists in a phosphatic band that forms the interface between the two lithologies. Further research indicates that the phosphatic band contains fossilized fish bones and teeth suggesting a marine origin. The processes of weathering release cadmium from the phosphatic band into the soil.

Health issues arising from high cadmium concentration has also been established in the central parts of Jamaica ([[:File:UNN_Medical_Geology_Fig_8.png|Figure 8]]). It occurs in the soil of a region with limestone and an overlying aluminum-rich bauxite deposit.<ref name=Wright /> Cadmium exists in a phosphatic band that forms the interface between the two lithologies. Further research indicates that the phosphatic band contains fossilized fish bones and teeth suggesting a marine origin. The processes of weathering release cadmium from the phosphatic band into the soil.

This has drastically increased the cadmium level in Jamaican soil to maximum values of 900 mg/kg against cadmium levels in other parts of the world which range from 0.1 mg/kg to 0.5 mk/kg (Wright et al, 2010).

This has drastically increased the cadmium level in Jamaican soil to maximum values of 900 mg/kg against cadmium levels in other parts of the world which range from 0.1 mg/kg to 0.5 mk/kg.<ref name=Wright />

The cadmium storage ability varies greatly in the various parts of plants, namely: the fruit, roots and the leaf as shown by tests conducted on food crops root crops, legumes and vegetables (Wright et al, 2010) (Table 5).

The cadmium storage ability varies greatly in the various parts of plants, namely: the fruit, roots and the leaf as shown by tests conducted on food crops root crops, legumes and vegetables (Table 5).

{| class="wikitable"

{| class="wikitable"

|-

|-

|+ Table 5: Concentrations of Cadmium in various plant species in Jamaica (Wright et al, 2010).

|+ {{Table number|5}}Concentrations of cadmium in various plant species in Jamaica.<ref name=Wright />

|-

|-

! Food Category || Number of Samples || Range (Conc. in mg/kg)

! Food Category || Number of Samples || Range (Conc. in mg/kg)

Amongst the above plant species, yam and carrot show the greatest ability to store cadmium. The concentration of cadmium in yam increases as the soil Cd level increases; it, however, decreases at low levels indicating toxicity as shown in [[:File:UNN_Medical_Geology_Fig_9.png|Figure 9]].

Amongst the above plant species, yam and carrot show the greatest ability to store cadmium. The concentration of cadmium in yam increases as the soil Cd level increases; it, however, decreases at low levels indicating toxicity as shown in [[:File:UNN_Medical_Geology_Fig_9.png|Figure 9]].

Toxicity effects of cadmium occurred in Jamaica as a result of food intake from Cd- contaminated food crops, legumes and vegetables. The mean Cd intake was 9.3 μg/kg bodyweight/week above WHO guideline of 7 μg/kg bodyweight/week while the drinking water standard for cadmium is 5μg l-1 (Wright et al, 2010).

Toxicity effects of cadmium occurred in Jamaica as a result of food intake from Cd- contaminated food crops, legumes and vegetables. The mean Cd intake was 9.3 μg/kg bodyweight/week above WHO guideline of 7 μg/kg bodyweight/week while the drinking water standard for cadmium is 5μg l-1 .<ref name=Wright />

===Health effects of radon gas===

===Health effects of radon gas===

Radon is a colourless inert gas formed from the radioactive disintegration of radium –the radioactive daughter of uranium. It has been established that there is a link between the levels of radon emitted by the rocks and that emitted by soils. The level of radon emitted by any rock depends on the quantity of uranium it contains which occurs in association with other minerals such as gold, phosphate and copper. This explains the scourge of lung cancer amongst uranium miners, as radon is carcinogenic. Radon emitted from most rocks travel to the surface through fractures and faults.<ref name=Fnklman2010b /> Its movement into buildings occurs through foundation cracks, cracks in the floor and walls below and above the surface. It can also enter through gaps in timber floors and around pipe fittings ([[:File:UNN_Medical_Geology_Fig_10.png|Figure 10]]).

Radon is a colourless inert gas formed from the radioactive disintegration of radium –the radioactive daughter of uranium. It has been established that there is a link between the levels of radon emitted by the rocks and that emitted by soils. The level of radon emitted by any rock depends on the quantity of uranium it contains which occurs in association with other minerals such as gold, phosphate and copper. This explains the scourge of lung cancer amongst uranium miners, as radon is carcinogenic. Radon emitted from most rocks travel to the surface through fractures and faults.<ref name=Fnklman2010b /> Its movement into buildings occurs through foundation cracks, cracks in the floor and walls below and above the surface. It can also enter through gaps in timber floors and around pipe fittings ([[:File:UNN_Medical_Geology_Fig_10.png|Figure 10]]).

African countries that have uranium as a natural resource include: South Africa which has the largest deposit of uranium in the continent–241,000 metric tons, Niger, Namibia, Gabon, Algeria, Botswana, Central African Republic, Chad. Others are: Egypt, Nigeria, Morocco, Mali, Madagascar, Malawi, Togo, Tanzania, Mauritania, Somalia, Guinea, Zambia and Lesotho.<ref name=Dvies />

African countries that have uranium as a natural resource include: South Africa, which has the largest deposit of uranium in the continent–241,000 metric tons; Niger; Namibia; Gabon; Algeria; Botswana; Central African Republic; and Chad. Others are: Egypt, Nigeria, Morocco, Mali, Madagascar, Malawi, Togo, Tanzania, Mauritania, Somalia, Guinea, Zambia and Lesotho.<ref name=Dvies />

===Health effects of geogenic dust===

===Health effects of geogenic dust===

====Health effects of asbestos====

====Health effects of asbestos====

Asbestos is an industrial term that comprises six different natural fibrous silicates. They include: grunerite, (Fe, Mg)7 Si8O22(OH)2, riebeckite, Na2(Fe,Mg)3Fe2Si8O22(OH)2, tremolite, Ca2Mg5Si8O22(OH)2, anthophyllite, (Mg, Fe)7Si8O22(OH)2 and actinolite, Ca2(Fe, Mg)5Si8O22(OH)2 all belonging to the amphibole group while the sixth mineral, chrysotile, Mg6(Si4O10)(OH)8 is a serpentine.<ref name=Ljung>Ljung, K., A. de Vos, A. Cook, and P. Weinstein, 2010, An Overview of Medical Geology Issues in Australia and Oceania. In: Selinus, O., Finkelman, R.B. and Centeno, J., Eds, Medical Geology – A Regional Synthesis. Springer, Germany, 107-135.</ref> These minerals can exist together as a homogenous mineral deposit or in combination with other minerals. Asbestos have found diverse applications owing to its flexibility, high tensile strength and resistance to heat, chemicals, and electricity. Thus, they are used in the manufacture of pipe lagging, asbestos roofing sheets, clutches and brake linings and insulation materials.<ref name=Ljung />

Asbestos is an industrial term that comprises six different natural fibrous silicates. They include: grunerite, (Fe, Mg)7 Si8O22(OH)2, riebeckite, Na2(Fe,Mg)3Fe2Si8O22(OH)2, tremolite, Ca2Mg5Si8O22(OH)2, anthophyllite, (Mg, Fe)7Si8O22(OH)2 and actinolite, Ca2(Fe, Mg)5Si8O22(OH)2 all belonging to the amphibole group while the sixth mineral, chrysotile, Mg6(Si4O10)(OH)8 is a serpentine.<ref name=Ljung>Ljung, K., A. de Vos, A. Cook, and P. Weinstein, 2010, An overview of medical geology issues in Australia and Oceania, ''in'' O. Selinus, R. B. Finkelman, and J. Centeno, eds., Medical geology—A regional synthesis: Berlin, Springer, p. 107–135.</ref> These minerals can exist together as a homogenous mineral deposit or in combination with other minerals. Asbestos have found diverse applications owing to its flexibility, high tensile strength and resistance to heat, chemicals, and electricity. Thus, they are used in the manufacture of pipe lagging, asbestos roofing sheets, clutches and brake linings and insulation materials.<ref name=Ljung />

Notwithstanding their many applications, they are extremely dangerous to human health. Because of their fibrous structure, asbestos can penetrate deep into the lungs when inhaled causing different forms of damage to the affected tissues. This disease is known as asbestosis–a fatal lung disease that saps the patient of strength. Such inhalation can also lead to lung cancer, cancer of the gastrointestinal tract and pleural mesothelioma.<ref name=Setal2010 />

Notwithstanding their many applications, they are extremely dangerous to human health. Because of their fibrous structure, asbestos can penetrate deep into the lungs when inhaled causing different forms of damage to the affected tissues. This disease is known as asbestosis–a fatal lung disease that saps the patient of strength. Such inhalation can also lead to lung cancer, cancer of the gastrointestinal tract and pleural mesothelioma.<ref name=Setal2010 />

====Shale and clay as food and food detoxifier====

====Shale and clay as food and food detoxifier====

Many African tribes eat clay as a source of food. It is intended to create a sensation of ‘fullness’ in the stomach. It is done as part of the menu in most cases. Geophagy is also practiced in times of famine. At such times, most people depend heavily on the eating of clay, shale or soil for survival as food supply dwindles, as a result of flood, drought or war. In South America, the Ottomac tribe resorts to the eating of soil when their local supply of fish and turtles declines during a time of annual flooding. The soil was prepared from alluvial sand molded into 12.5 cm–15 cm diameter balls.<ref name=Setal2013 /> Food shortage has also been reported as the cause of geophagy in Malawi.<ref name=Setal2013 />

Many African tribes eat clay as a source of food. It is intended to create a sensation of ‘fullness’ in the stomach. It is done as part of the menu in most cases. Geophagy is also practiced in times of famine. At such times, most people depend heavily on the eating of clay, shale or soil for survival as food supply dwindles, as a result of flood, drought or war. In South America, the Ottomac tribe resorts to the eating of soil when their local supply of fish and turtles declines during a time of annual flooding. The soil was prepared from [[alluvial]] sand molded into 12.5 cm–15 cm diameter balls.<ref name=Setal2013 /> Food shortage has also been reported as the cause of geophagy in Malawi.<ref name=Setal2013 />

In addition, shale, clays and soils are used as food detoxifiers. This is practiced mostly during times of famine to detoxify toxic food items from plant origin before consumption. Clay is used in this regard because of its cation exchange capacity so that potentially harmful chemicals get adsorbed into the clay structure making the food item harmless. This is practiced by some African tribes who use clay to detoxify wild yam, Dioscorea dumentorum, during famine. The use of clays and soil to detoxify wild plant foodstuffs is not restricted to Africans alone, the Aymara and Quechua people who live on the Andes of Bolivia and Peru consume wild potatoes by dipping them in clay slurry. The clay slurry effectively removes potentially toxic glycoalkaloids and, thus, renders it harmless to the natives.<ref name=Setal2013 />

In addition, shale, clays and soils are used as food detoxifiers. This is practiced mostly during times of famine to detoxify toxic food items from plant origin before consumption. Clay is used in this regard because of its cation exchange capacity so that potentially harmful chemicals get adsorbed into the clay structure making the food item harmless. This is practiced by some African tribes who use clay to detoxify wild yam, Dioscorea dumentorum, during famine. The use of clays and soil to detoxify wild plant foodstuffs is not restricted to Africans alone, the Aymara and Quechua people who live on the Andes of Bolivia and Peru consume wild potatoes by dipping them in clay slurry. The clay slurry effectively removes potentially toxic glycoalkaloids and, thus, renders it harmless to the natives.<ref name=Setal2013 />

====Geophagy for pharmaceutical reasons====

====Geophagy for pharmaceutical reasons====

From ancient times, soils and clays had been used as pharmaceuticals by humans for the treatment of various diseases. Such practices still persist in the modern world. In Europe, the various varieties of the soil, terra sigillata, have been used for over 2,000 years for the treatment of a number of health problems such as bites and stings of venomous animals, malignant ulcers, nose bleeds, gout, dysentery and poisoning.<ref name=Setal2013 /> The effectiveness of terra sigillata is attributed to the ion exchange capacity of the soil. As a result, bentonite– enriched in the clay mineral montmorillonite– is extensively used in the developed nations as an antidote to poisons. Also, kaolin is used in the treatment of gastrointestinal disorders such as gastrodynia (stomachache), dyspepsia (acid indigestion), nausea and diarrhea.

From ancient times, soils and clays had been used as pharmaceuticals by humans for the treatment of various diseases. Such practices still persist in the modern world. In Europe, the various varieties of the soil, terra sigillata, have been used for over 2,000 years for the treatment of a number of health problems such as bites and stings of venomous animals, malignant ulcers, nose bleeds, gout, dysentery and poisoning.<ref name=Setal2013 /> The effectiveness of terra sigillata is attributed to the ion exchange capacity of the soil. As a result, [[bentonite]]– enriched in the clay mineral montmorillonite– is extensively used in the developed nations as an antidote to poisons. Also, kaolin is used in the treatment of gastrointestinal disorders such as gastrodynia (stomachache), dyspepsia (acid indigestion), nausea and diarrhea.

In Nigeria, 400–500 tonnes of Paleocene shale collected from the village of Uzalla situated in Orhionmw, Edo State is used for the treatment of dysenteric ailments; this is called eko by the villagers.<ref name=Setal2013 />

In Nigeria, 400–500 tonnes of Paleocene shale collected from the village of Uzalla situated in Orhionmw, Edo State is used for the treatment of dysenteric ailments; this is called eko by the villagers.<ref name=Setal2013 />

====Dangers of Geophagy====

====Dangers of Geophagy====

Despite the various benefits of geophagy, it can be detrimental to human health. The cation exchange capacity and the adsorption potential of clay and shale can lead to the deficiency of certain elements in the body. For instance, in Turkey, iron-deficiency anemia has been linked to the consumption of clays especially sepiolite and montmorillonite of high capillary electrochromatography.<ref name=Abraham>Abraham, P. W., 2013, Geophagy and the Involuntary Ingestion of Soil. In: O. Selinus, Essentials of Medical Geology: Springer Netherlands, pp. 433-454.</ref> This is caused by the effectiveness of clays to adsorb iron. In addition, the consumption of clay has been confirmed to cause potassium deficiency–a condition known as hypokalemia. It is reflected by low concentration of potassium in the blood. In a situation whereby there is concurrent deficiency of iron and potassium, a disease known as cachexia Africana results. This can, however, be treated by iron and potassium supplementation programmes.

Despite the various benefits of geophagy, it can be detrimental to human health. The cation exchange capacity and the adsorption potential of clay and shale can lead to the deficiency of certain elements in the body. For instance, in Turkey, iron-deficiency anemia has been linked to the consumption of clays especially sepiolite and montmorillonite of high capillary electrochromatography.<ref name=Abraham>Abraham, P. W., 2013, Geophagy and the involuntary ingestion of soil, ''in'' O. Selinus, Essentials of medical geology: Amsterdam, Springer, p. 433–454.</ref> This is caused by the effectiveness of clays to adsorb iron. In addition, the consumption of clay has been confirmed to cause potassium deficiency–a condition known as hypokalemia. It is reflected by low concentration of potassium in the blood. In a situation whereby there is concurrent deficiency of iron and potassium, a disease known as cachexia Africana results. This can, however, be treated by iron and potassium supplementation programs.

In Turkey, the consumption of soil by women and children has been noted to cause the combined deficiency of iron and zinc.<ref name=Abraham /> According to a research conducted, deficiency of zinc leads to growth retardation and delayed puberty. Thus, for persons that have low concentration of zinc in the blood, geophagy helps to further lower the level of zinc in the blood. However, zinc supplementation programmes have been supremely effective in improving growth and normal puberty maturation in this region.

In Turkey, the consumption of soil by women and children has been noted to cause the combined deficiency of iron and zinc.<ref name=Abraham /> According to a research conducted, deficiency of zinc leads to growth retardation and delayed puberty. Thus, for persons that have low concentration of zinc in the blood, geophagy helps to further lower the level of zinc in the blood. However, zinc supplementation programs have been supremely effective in improving growth and normal puberty maturation in this region.

In an environment where the soil is contaminated with lead, geophagy could expose little children to lead poisoning. This could lead to damage to the developing brain and nervous system. Lead is particularly dangerous to young children as research has shown that there is no safe level for lead in children.

In an environment where the soil is contaminated with lead, geophagy could expose little children to lead poisoning. This could lead to damage to the developing brain and nervous system. Lead is particularly dangerous to young children as research has shown that there is no safe level for lead in children.

From ancient times, man has explored geologic materials and put them to use for his well- being. Some of them had been used domestically while others have many industrial, as well as medical applications, depending on available technology.

From ancient times, man has explored geologic materials and put them to use for his well- being. Some of them had been used domestically while others have many industrial, as well as medical applications, depending on available technology.

Therapeutic application of medical geology refers to the use of geological materials in the treatment of diseases. Nigeria has a lot of potentials for the therapeutic applications of geologic materials. For instance, the country is blessed with thermal mineralized waters in various parts of the nation such as the Ikogosi Warm Spring in Ekiti State, the mineralized thermal springs at Awe in Nasarawa State and those in the onshore/offshore locations of Delta, Rivers, Cross Rivers, Edo, Bayelsa and Imo States. In addition, Nigeria is blessed with abundance of medicinal clays such as kaolin and bentonite in most states of the federation. Also, there is abundance of peat, trona and potash in some states (after Nghargbu et al, 2013<ref name=Ngha>Nghargbu, K., Ponikowska, I., Latour, T., Kurowska, E., Schoeneich, K., and Alagbe, S.A., 2013a. Balneo-therapeutic Quality of Water from Thermal Chlorosodic Springs of the Middle Benue Trough, Nigeria. Unpublished Work, Nasarawa State University, Keffi, Nigeria,1-9.</ref><ref name=Nghb>Nghargbu, K., Ponikowska, I., Latour, T., Kurowska, E., Schoeneich, K., and Alagbe, S.A. 2013b. Geomedical Resources Inventory: The Nigerian Content. Unpublished Work, Nasarawa State University, Keffi, Nigeria, 1-15.</ref>).

Therapeutic application of medical geology refers to the use of geological materials in the treatment of diseases. Nigeria has a lot of potentials for the therapeutic applications of geologic materials. For instance, the country is blessed with thermal mineralized waters in various parts of the nation such as the Ikogosi Warm Spring in Ekiti State, the mineralized thermal springs at Awe in Nasarawa State and those in the onshore/offshore locations of Delta, Rivers, Cross Rivers, Edo, Bayelsa and Imo States. In addition, Nigeria is blessed with abundance of medicinal clays such as kaolin and [[bentonite]] in most states of the federation. Also, there is abundance of peat, trona and potash in some states (after Nghargbu et al, 2013<ref name=Ngha>Nghargbu, K., I. Ponikowska, T. Latour, E. Kurowska, K. Schoeneich, and S. A., Alagbe, 2013a, Balneo-therapeutic quality of water from thermal chlorosodic springs of the Middle Benue Trough, Nigeria: Unpublished paper, Nasarawa State University, Keffi, Nigeria, 9 p.</ref><ref name=Nghb>Nghargbu, K., I. Ponikowska, T. Latour, E. Kurowska, K. Schoeneich, and S. A. Alagbe, 2013b, Geomedical Resources Inventory: The Nigerian Content: Unpublished work, Nasarawa State University, Keffi, Nigeria, 15 p.</ref>).

Sadly, lack of technological know-how and fewer number of medical geology practitioners in Nigeria have limited the extraction of these resources for medical purposes.

Sadly, lack of technological know-how and fewer number of medical geology practitioners in Nigeria have limited the extraction of these resources for medical purposes.

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UNN_Medical_Geology_Fig_12.png|{{figure number|12}}Tangarahu Spring, Awe, Nigeria.<ref name=Ngha /><ref name=Nghb />

UNN_Medical_Geology_Fig_12.png|{{figure number|12}}Tangarahu Spring, Awe, Nigeria.<ref name=Ngha /><ref name=Nghb />

UNN_Medical_Geology_Fig_13.png|{{figure number|13}}Geology of Awe and environs. QUATERNARY (A) Alluvium (B) Tertiary To Recent Volcanics; CRETACEOUS (C) Nkporo Shale Group (D) Awgu-Ndeabo Shale Group (E) Ezeaku Shale Group (F) Asu River Group; PRECAMBRIAN (G) Basement Complex (H) Anticlinal Axis (I) Synclinal Axis (J) Fracture.<ref name=Ngha /><ref name=Nghb />]]

UNN_Medical_Geology_Fig_13.png|{{figure number|13}}Geology of Awe and environs. Quaternary (A) Alluvium (B) Tertiary To Recent Volcanics; Cretaceous (C) Nkporo Shale Group (D) Awgu-Ndeabo Shale Group (E) Ezeaku Shale Group (F) Asu River Group; Precambrian (G) Basement Complex (H) Anticlinal Axis (I) Synclinal Axis (J) Fracture.<ref name=Ngha /><ref name=Nghb />

</gallery>

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[[File:UNN_Medical_Geology_Fig_15.png|thumb|400px|{{figure number|15}}Application of bentonite cream on the face.<ref name=Ngha /><ref name=Nghb />]]

[[File:UNN_Medical_Geology_Fig_15.png|thumb|400px|{{figure number|15}}Application of bentonite cream on the face.<ref name=Ngha /><ref name=Nghb />]]

Bentonite is an absorbent aluminum phylosilicate rock containing mostly montmorillonite. It is formed mainly from volcanic ash. The name comes from the largest known deposit of bentonite clay located in Fort Benton, Wyoming, USA. It is a unique clay due to its ability to produce electronegative charge when hydrated giving it the ability to attract and neutralize toxins which are electropositive. When mixed with water, bentonite rapidly swells open like a highly porous sponge, making the toxins and heavy metal to be drawn in through electrical attraction without leaching away any of its beneficial elements. This phenomenon prevents toxic molecules from passing through the walls of the intestines and entering the bloodstream; instead, they are eliminated from the body through the kidneys.

[[Bentonite]] is an absorbent aluminum phylosilicate rock containing mostly montmorillonite. It is formed mainly from volcanic ash. The name comes from the largest known deposit of bentonite clay located in Fort Benton, Wyoming, USA. It is a unique clay due to its ability to produce electronegative charge when hydrated giving it the ability to attract and neutralize toxins which are electropositive. When mixed with water, bentonite rapidly swells open like a highly porous sponge, making the toxins and heavy metal to be drawn in through electrical attraction without leaching away any of its beneficial elements. This phenomenon prevents toxic molecules from passing through the walls of the intestines and entering the bloodstream; instead, they are eliminated from the body through the kidneys.

Based on the above properties, bentonite is an important healing clay. It can be applied on the skin to remove eczema and also applied on the face ([[:File:UNN_Medical_Geology_Fig_15.png|Figure 15]]) and other parts of the body as a cream where it leaves the skin smooth and radiant.<ref>Knishinsky, R., 1998, The Clay Cure. Healing Arts Press, Rochester, 112p.</ref>

Based on the above properties, bentonite is an important healing clay. It can be applied on the skin to remove eczema and also applied on the face ([[:File:UNN_Medical_Geology_Fig_15.png|Figure 15]]) and other parts of the body as a cream where it leaves the skin smooth and radiant.<ref>Knishinsky, R., 1998, The clay cure: Rochester, New York, Healing Arts Press, 112 p.</ref>

===Kaolin===

===Kaolin===

===Milk of Magnesia===

===Milk of Magnesia===

[[File:UNN_Medical_Geology_Fig_16.png|thumb|400px|{{figure number|16}}Milk of Magnesia (sourced from: www.bing.com/images on 31/03/2014)]]

[[File:UNN_Medical_Geology_Fig_16.png|thumb|400px|{{figure number|16}}Milk of Magnesia]]

Milk of magnesia is a name given to magnesium hydroxide – an inorganic compound with the formula, “Mg(OH)2”. It forms a milk-like appearance when in suspension, hence the name. The solid mineral form of magnesium hydroxide is brucite [Mg(OH)2] which occurs in clay minerals especially in chlorite. Brucite occupies the interlayer position which is normally occupied by monovalent and divalent cations such as Na+, K+, Mg+ and Ca+ in chlorite. In this manner, chlorite interlayer is cemented by brucite and can neither swell nor shrink (Zumdahl, 2009).

Milk of magnesia is a name given to magnesium hydroxide – an inorganic compound with the formula, “Mg(OH)2”. It forms a milk-like appearance when in suspension, hence the name. The solid mineral form of magnesium hydroxide is brucite [Mg(OH)2] which occurs in clay minerals especially in chlorite. Brucite occupies the interlayer position which is normally occupied by monovalent and divalent cations such as Na+, K+, Mg+ and Ca+ in chlorite. In this manner, chlorite interlayer is cemented by brucite and can neither swell nor shrink.<ref>Zumdahl, S. S., 2009, Chemical principles: New York, Houghton Mifflin, 120 p.</ref>

Milk of magnesia is used as an antacid to neutralize stomach acid. Hydroxide ions from the Mg(OH)2 combine with acidic hydroxide (H+) ions produced from hydrochloric acid by parietal cells in the stomach to produce water. It is made into capsules and chewable tablets for use against constipation and indigestion ([[:File:UNN_Medical_Geology_Fig_16.png|Figure 16]]).

Milk of magnesia is used as an antacid to neutralize stomach acid. Hydroxide ions from the Mg(OH)2 combine with acidic hydroxide (H+) ions produced from hydrochloric acid by parietal cells in the stomach to produce water. It is made into capsules and chewable tablets for use against constipation and indigestion ([[:File:UNN_Medical_Geology_Fig_16.png|Figure 16]]).

As a laxative, milk of magnesia absorbs fluid from the body, through osmotic pressure, into the lumen of the small intestine while retaining the fluid already in the small intestine.<ref>Pradyot, P., 2002. Handbook of Inorganic Chemicals. McGraw-Hill, New York, 186p.</ref> First, Mg2+ is poorly absorbed from the intestinal tract, so it draws water from the surrounding tissue by osmosis. Not only does this increase the water content, it softens the faeces and increases the volume of faeces in the intestine which naturally stimulates intestinal motility. Furthermore, Mg2+ ions cause the release of cholecystokinin (CCK) which results in intraluminal accumulation of water, electrolytes and increased intestinal motility. This stimulates the nerves of the colon to distend leading to peristalsis culminating in the evacuation of its contents.

As a laxative, milk of magnesia absorbs fluid from the body, through osmotic pressure, into the lumen of the small intestine while retaining the fluid already in the small intestine.<ref>Pradyot, P., 2002, Handbook of inorganic chemicals: New York, McGraw-Hill, 186 p.</ref> First, Mg2+ is poorly absorbed from the intestinal tract, so it draws water from the surrounding tissue by osmosis. Not only does this increase the water content, it softens the feces and increases the volume of feces in the intestine which naturally stimulates intestinal motility. Furthermore, Mg2+ ions cause the release of cholecystokinin (CCK) which results in intraluminal accumulation of water, electrolytes and increased intestinal motility. This stimulates the nerves of the colon to distend leading to peristalsis culminating in the evacuation of its contents.

===Plaster of Paris===

===Plaster of Paris===

===Alkaline Water===

===Alkaline Water===

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UNN_Medical_Geology_Fig_18.png|{{figure number|18}}Increase in pH due to alkaline water intake<ref name=TK>Tan Koon, P. M., 2013, [www.alkaflask.blogspot.sg  AlkaFlask Potable Alkaline Water Maker].</ref>

UNN_Medical_Geology_Fig_18.png|{{figure number|18}}Increase in pH due to alkaline water intake<ref name=TK>Tan Koon, P. M., 2013, [http://alkaflask.blogspot.com/ AlkaFlask Potable Alkaline Water Maker].</ref>

UNN_Medical_Geology_Fig_19.png|{{figure number|19}}Arrangement of different geologic materials in the alkaline water flask.<ref name=TK>

UNN_Medical_Geology_Fig_19.png|{{figure number|19}}Arrangement of different geologic materials in the alkaline water flask.<ref name=TK>

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Medical geology is also concerned with the use of geologic materials for the treatment of various diseases. Five chlorosodic warm springs at Awe namely: Ruwan Akiri, Ruwan Dumi, Tangarahu Ruwan Zafi and Bitrus have proven to be efficient in the treatment of orthopaedic injuries, arterial high blood pressure, poor circulation of blood in the lower limbs caused either by diabetes or sclerosis. They can also be used in the treatment of polineuropathy, pareses and atrophy of muscles. The mineralized water is used through balneotherapy– the science of treating diseases by bathing in mineralized waters. Chlorosodic water from these springs can also be applied in treatment through oral intake.

Medical geology is also concerned with the use of geologic materials for the treatment of various diseases. Five chlorosodic warm springs at Awe namely: Ruwan Akiri, Ruwan Dumi, Tangarahu Ruwan Zafi and Bitrus have proven to be efficient in the treatment of orthopaedic injuries, arterial high blood pressure, poor circulation of blood in the lower limbs caused either by diabetes or sclerosis. They can also be used in the treatment of polineuropathy, pareses and atrophy of muscles. The mineralized water is used through balneotherapy– the science of treating diseases by bathing in mineralized waters. Chlorosodic water from these springs can also be applied in treatment through oral intake.

Medical geology has also found bentonite be a potential pharmaceutical material. When used, it removes toxins, bacteria and heavy metals from the body by producing negative ions when hydrated. It is applied on the skin for the removal of eczema and on the face to make it smooth and radiant.

Medical geology has also found [[bentonite]] to be a potential pharmaceutical material. When used, it removes toxins, bacteria and heavy metals from the body by producing negative ions when hydrated. It is applied on the skin for the removal of eczema and on the face to make it smooth and radiant.

The mineral brucite from chlorite is used as an excellent antacid and a laxative in the form of magnesium hydroxide, commonly known as milk of magnesia. It is applied in the treatment of constipation, indigestion and heartburn.

The mineral brucite from chlorite is used as an excellent antacid and a laxative in the form of magnesium hydroxide, commonly known as milk of magnesia. It is applied in the treatment of constipation, indigestion and heartburn.

==References==

==References==

{{reflist}}

{{reflist}}

 

* Wright, P.R.D., Rattray, R. and Lalor, G., 2010. A Regional Perspective of Medical Geology– Cadmium in Jamaica. In: Selinus, O., Finkelman, R.B. and Centeno, J.A., (eds) 2010. Medical Geology: A Regional Synthesis, 36–45.

* [http://www.medicaljobsaustralia.com/ Medical Jobs Australia]

* Wuyi, W., Linsheng, Y., Shaofan, H. and Jian’an T., 2003. Mitigation of Endemic Arsenocosis with Selenium: an Example from China. HCWSkinner ARBerger, 51–56.

* [http://www.medicaljobsaustralia.com/jobs/australia/nurses-and-midwives/ Nursing Jobs]

* Zheng, B., Wang, B. and Finkelman, R.B., 2010. Medical Geology in China: Then and Now. In: Selinus, O., Finkelman, R.B. and Centeno, J.A., (eds), Medical Geology: A Regional Synthesis, 303–319.