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==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 (Selinus et al, 2001). 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 (Selinus and Finkelman, 2011).

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>

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 (Skinner, 2007).

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 (Skinner, 2007).

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 (Selinus, 2004).

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>

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 (Selinus, 2004).

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, 5(3), 273-281.</ref>

===Multidisciplinary nature of medical geology===

===Multidisciplinary nature of medical geology===

[[File:UNN_Medical_Geology_Fig_1.png|thumb|400px|{{figure number|1}}Venn diagram showing the multidisciplinary nature of medical geology (Selinus and Finkelman, 2011).]]

[[File:UNN_Medical_Geology_Fig_1.png|thumb|400px|{{figure number|1}}Venn diagram showing the multidisciplinary nature of medical geology.<ref name=S&F2011 />]]

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]], Selinus, and Finkelman, 2011).

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 (Selinus et al, 2013).

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>

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)/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.

[[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. Elsevier, Amsterdam, 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 (Selinus and Frank, 2000). 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, 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>

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 (Skinner, 2007).

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 (Skinner, 2007).

===Biological classification of elements===

===Biological classification of elements===

[[File:UNN_Medical_Geology_Fig_3.png|thumb|400px|{{figure number|3}}Periodic table illustrating major elements (pink), minor elements (blue), trace elements (yellow), and noble gases (gray) in the biosphere. Those in green are essential trace elements. Known established toxic elements are shown in red (Selinus et al, 2013).]]

[[File:UNN_Medical_Geology_Fig_3.png|thumb|400px|{{figure number|3}}Periodic table illustrating major elements (pink), minor elements (blue), trace elements (yellow), and noble gases (gray) in the biosphere. Those in green are essential trace elements. Known established toxic elements are shown in red.<ref name=Setal2013 />]]

Good understanding of health issues arising from geologic materials comes from sound knowledge of the classification of elements from the biological point of view because not all elements have been proven to cause health problems. Therefore, medical geology is mainly geared towards identifying and understanding the harmful elements (Selinus et al, 2013).

Good understanding of health issues arising from geologic materials comes from sound knowledge of the classification of elements from the biological point of view because not all elements have been proven to cause health problems. Therefore, medical geology is mainly geared towards identifying and understanding the harmful elements.<ref name=Setal2013 />

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 (Selinus et al, 2013).

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 />

Minor elements are those elements that are needed in moderate quantities; each has a concentration of 0.1% to 1.0% in the body (Selinus et al, 2013). 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, 151(9), 913-920.</ref> They are highly variable in their abundance in various rocks (Table 1).

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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 (Selinus et al, 2013).

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/streams. In addition, they can be released during volcanic eruptions.

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 (Selinus et al, 2010).

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>

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 (Selinus et al, 2013).

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 (2013), 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 (Skinner, 2007). 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 (Skinner, 2007). These emanate from groundwater which might have leached both toxic and non-toxic elements from rocks through which it flowed.

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 (2010). 22 persons out of 45 persons tested positive to minor arsenosis (Selinus et al, 2010).

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====

# It decreases the ageing process by maintaining the length of telomere and by reducing the oxidative stress of the mitochondria;

# It decreases the ageing process by maintaining the length of telomere and by reducing the oxidative stress of the mitochondria;

# It reduces the risk of asthma, arthritis and muscular dystrophy as a result of the anti-oxidative nature of selenoenzymes; and

# It reduces the risk of asthma, arthritis and muscular dystrophy as a result of the anti-oxidative nature of selenoenzymes; and

# Trivializes the effects of depression and anxiety (Selinus et al, 2013).

# Trivializes the effects of depression and anxiety.<ref name=Setal2013 />

===Toxicity effects of excess fluoride===

===Toxicity effects of excess fluoride===

[[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 (Selinus et al, 2010).]]

[[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 (Schamschula and Barmes, 1981).

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>

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 (Selinus et al, 2013). 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 (Schamschula and Barmes, 1981). 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]]).

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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 (Selinus et al, 2010).

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 impacts of harmattan dust====

====Health impacts of harmattan dust====

[[File:UNN_Medical_Geology_Fig_11.png|thumb|400px|{{figure number|11}}Dust storm as it approaches Bagdad, Iraq (Selinus et al, 2010).]]

[[File:UNN_Medical_Geology_Fig_11.png|thumb|400px|{{figure number|11}}Dust storm as it approaches Bagdad, Iraq.<ref name=Setal2010 />]]

In Nigeria, the most important source of dust is the Sahara Desert. Its influence arrives in Nigeria in the form of harmattan mainly in the months of December, January and February. Harmattan wind transports very fine particulate matter which may be toxic inorganic or organic particles and/or pathogens ([[:File:UNN_Medical_Geology_Fig_11.png|Figure 11]]). This triggers or strengthens respiratory problems such as asthma and catarrh.

In Nigeria, the most important source of dust is the Sahara Desert. Its influence arrives in Nigeria in the form of harmattan mainly in the months of December, January and February. Harmattan wind transports very fine particulate matter which may be toxic inorganic or organic particles and/or pathogens ([[:File:UNN_Medical_Geology_Fig_11.png|Figure 11]]). This triggers or strengthens respiratory problems such as asthma and catarrh.

Another important source of dust in Nigeria is unpaved roads. The passage of traffic cause particulate matter to rise from roads causing untold damage to people’s respiratory systems.

Another important source of dust in Nigeria is unpaved roads. The passage of traffic cause particulate matter to rise from roads causing untold damage to people’s respiratory systems.

The health effect of the dust depends on the size: the bigger particles affect the airways and lungs while fine particles go farther to affect parts of the alveolar. In addition, the composition of the dust goes a long way to determine the possible health effect; it can be organic or inorganic. Organic dust contains particles of animal, vegetable and those of microbial origin such as bacteria and fungi (Selinus et al, 2010). This type of dust causes allergic aveolitis. Organic dust may contain minerals such as quartz, feldspar and mica produced as a result of the abrasion action of the wind. These can get dissolved in the blood stream causing damage in the kidney, brain and other organs. Generally, the composition is dependent on the type of rock from which the dust was derived.

The health effect of the dust depends on the size: the bigger particles affect the airways and lungs while fine particles go farther to affect parts of the alveolar. In addition, the composition of the dust goes a long way to determine the possible health effect; it can be organic or inorganic. Organic dust contains particles of animal, vegetable and those of microbial origin such as bacteria and fungi.<ref name=Setal2010 /> This type of dust causes allergic aveolitis. Organic dust may contain minerals such as quartz, feldspar and mica produced as a result of the abrasion action of the wind. These can get dissolved in the blood stream causing damage in the kidney, brain and other organs. Generally, the composition is dependent on the type of rock from which the dust was derived.

====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: 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 />

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 (Selinus et al, 2010).

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 />

The toxicity of asbestos is determined by three factors: fiber dimension, bio-persistence and dosage. Fiber dimension refers to the relationship between fiber length and diameter; this decides where the asbestos would be deposited in the lung. With regard to fiber dimension, lung cancer has primarily been associated with fibers which are greater than 10 μm in length and greater than 0.15 μm in diameter; mesothelioma is associated with fibers which are greater than 5 μm in length and less than 0.1 μm in diameter while fibrosis has been associated with particles >5 μm in length (Selinus et al, 2013).

The toxicity of asbestos is determined by three factors: fiber dimension, bio-persistence and dosage. Fiber dimension refers to the relationship between fiber length and diameter; this decides where the asbestos would be deposited in the lung. With regard to fiber dimension, lung cancer has primarily been associated with fibers which are greater than 10 μm in length and greater than 0.15 μm in diameter; mesothelioma is associated with fibers which are greater than 5 μm in length and less than 0.1 μm in diameter while fibrosis has been associated with particles >5 μm in length.<ref name=Setal2013 />

Bio-persistence of asbestos is influenced by the rate and site of deposition; high rate of deposition can overwhelm macrophages and thus lead to toxicity effects. Other bio- persistence factors are rate of clearance, solubility, rate and pattern of breakage and ease of translocation across membranes.

Bio-persistence of asbestos is influenced by the rate and site of deposition; high rate of deposition can overwhelm macrophages and thus lead to toxicity effects. Other bio- persistence factors are rate of clearance, solubility, rate and pattern of breakage and ease of translocation across membranes.

Silica is an important component of diatomites–a resource mined and produced in Kenya, Ethiopia, Algeria and South Africa.<ref name=Dvies /> It is used in the manufacture of fillers, filters and may be used in making mild abrasives.

Silica is an important component of diatomites–a resource mined and produced in Kenya, Ethiopia, Algeria and South Africa.<ref name=Dvies /> It is used in the manufacture of fillers, filters and may be used in making mild abrasives.

Silica dust can be inhaled at quarries and at diatomite mines. It is most dangerous at the stage of calcining resulting to silicosis. It also affects people that live near the mine and processing plants. Worst of all, silicosis is contagious. In addition, its deposition in the lung is proven to cause fatal lung cancer (Selinus et al, 2013).

Silica dust can be inhaled at quarries and at diatomite mines. It is most dangerous at the stage of calcining resulting to silicosis. It also affects people that live near the mine and processing plants. Worst of all, silicosis is contagious. In addition, its deposition in the lung is proven to cause fatal lung cancer.<ref name=Setal2013 />

However, not all forms of silica cause silicosis. The dangerous types are the crystalline forms –quartz, chrystobalite and tridymite. They cause illnesses such as nodular pulmonary fibrosis (also known as silicosis), lung cancer, bronchitis and secondary heart diseases (Selinus et al, 2013).

However, not all forms of silica cause silicosis. The dangerous types are the crystalline forms –quartz, chrystobalite and tridymite. They cause illnesses such as nodular pulmonary fibrosis (also known as silicosis), lung cancer, bronchitis and secondary heart diseases.<ref name=Setal2013 />

===Geophagy===

===Geophagy===

Geophagy refers to the deliberate consumption of soil, clays and shale in some cultures. The practice is most common amongst the female folk especially during pregnancy. They say it is beneficial for the development of the fetus and helps to overcome anxiety and agitation (Selinus et al, 2013). However, the practice is not limited to women– men and children practice geophagy. Reasons abound why people eat clays, shales and soils.

Geophagy refers to the deliberate consumption of soil, clays and shale in some cultures. The practice is most common amongst the female folk especially during pregnancy. They say it is beneficial for the development of the fetus and helps to overcome anxiety and agitation.<ref name=Setal2013 /> However, the practice is not limited to women– men and children practice geophagy. Reasons abound why people eat clays, shales and soils.

====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 (Selinus, et al, 2013). Food shortage has also been reported as the cause of geophagy in Malawi (Selinus, et al, 2013).

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 (Selinus et al, 2013).

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 (Selinus et al, 2013). 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 (Selinus, et al, 2013).

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 />

====Geophagy for cultural reasons====

====Geophagy for cultural reasons====

====Nutritional reasons for indulging in geophagy====

====Nutritional reasons for indulging in geophagy====

Laboratory analyses have been used to authenticate the assumption by local geophagist that clays, shales and soils supply nutrients. For instance, the ability of clays to supply nutrients is dependent on the cation exchange capability of the clays. In the stomach, the ingested clay in contact with the acidity of the stomach releases elements such as calcium and iron through cation exchange reactions. As a result, pregnant women consume clays and shales to improve on their daily calcium levels needed for the fetal skeletal growth and development. According to Selinus et al( 2013), during the first trimester of pregnancy, ingested clays absorb dietary toxins which are harmful to the embryo and help to reduce the common symptoms of pregnancy sickness. In the second trimester of pregnancy, ingested clays help to reduce pregnancy-induced hypertension. The daily calcium level increases from 800 to 1,200 mg day-1 (Selinus et al, 2013).

Laboratory analyses have been used to authenticate the assumption by local geophagist that clays, shales and soils supply nutrients. For instance, the ability of clays to supply nutrients is dependent on the cation exchange capability of the clays. In the stomach, the ingested clay in contact with the acidity of the stomach releases elements such as calcium and iron through cation exchange reactions. As a result, pregnant women consume clays and shales to improve on their daily calcium levels needed for the fetal skeletal growth and development. According to Selinus et al,<ref name=Setal2013 /> during the first trimester of pregnancy, ingested clays absorb dietary toxins which are harmful to the embryo and help to reduce the common symptoms of pregnancy sickness. In the second trimester of pregnancy, ingested clays help to reduce pregnancy-induced hypertension. The daily calcium level increases from 800 to 1,200 mg day-1.<ref name=Setal2013 />

Results for analyses conducted on various samples of geophagical materials obtained from several countries are shown in the Table 6.

Results for analyses conducted on various samples of geophagical materials obtained from several countries are shown in the Table 6.

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.

Additionally, consumption of biological components of soils such as eggs and larvae of bacteria and fungi can lead to various kinds of diseases. For instance, ascariasis and trichuriasis are caused by the ingestion of Ascaris lumbricoides and Trichuris trichiura eggs respectively. Toxocariasis occurs through infection with the larvae of Toxocara canis or T. cati. Furthermore, hookworm is consumed through oral intake of Ancylostoma duodenale and A. ceylanicum (Selinus et al, 2013).

Additionally, consumption of biological components of soils such as eggs and larvae of bacteria and fungi can lead to various kinds of diseases. For instance, ascariasis and trichuriasis are caused by the ingestion of Ascaris lumbricoides and Trichuris trichiura eggs respectively. Toxocariasis occurs through infection with the larvae of Toxocara canis or T. cati. Furthermore, hookworm is consumed through oral intake of Ancylostoma duodenale and A. ceylanicum.<ref name=Setal2013 />

==Therapeutic applications of medical geology==

==Therapeutic applications of medical geology==

===Kaolin===

===Kaolin===

Kaolin is made up of the clay mineral, kaolinite with the chemical composition Al2Si2O5(OH)4. Kaolinite is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra. It is also known as China clay. Kaolinite has low shrink-swell capacity and low cation exchange capacity (Selinus et al, 2013). It is a soft, earthy, usually white mineral produced by the chemical weathering of aluminosilicate minerals such as feldspars. In many parts of the world, it is colored pink, orange or red by iron oxide, giving it a distinct rust hue. Lighter concentrations yield white, yellow or light orange colours (Selinus et al, 2013).

Kaolin is made up of the clay mineral, kaolinite with the chemical composition Al2Si2O5(OH)4. Kaolinite is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra. It is also known as China clay. Kaolinite has low shrink-swell capacity and low cation exchange capacity.<ref name=Setal2013 /> It is a soft, earthy, usually white mineral produced by the chemical weathering of aluminosilicate minerals such as feldspars. In many parts of the world, it is colored pink, orange or red by iron oxide, giving it a distinct rust hue. Lighter concentrations yield white, yellow or light orange colours.<ref name=Setal2013 />

Kaolin is used for the treatment of mild-to-moderate diarrhoea, dysentery and cholera. It is also used in combination products for the treatment of inflammation and soreness of the mouth. Such products are also used for the treatment of ulcers and inflammation of the large intestine.<ref name=Ngha /><ref name=Nghb />

Kaolin is used for the treatment of mild-to-moderate diarrhoea, dysentery and cholera. It is also used in combination products for the treatment of inflammation and soreness of the mouth. Such products are also used for the treatment of ulcers and inflammation of the large intestine.<ref name=Ngha /><ref name=Nghb />

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* 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.

* 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.

* Tan Koon, P.M., 2013. AlkaFlask Potable Alkaline Water Maker. Sourced from www.alkaflask.blogspot.sg on 13/02/2014.

* Tan Koon, P.M., 2013. AlkaFlask Potable Alkaline Water Maker. Sourced from www.alkaflask.blogspot.sg on 13/02/2014.