Medical Geology is an emerging scientific discipline that examines the impacts that geologic materials and processes have on human and ecosystem health. Medical Geology:
· Identifies and characterizes natural and anthropogenic sources of harmful materials in the environment.
· Predicts the movement and alteration of chemical, infectious, and other disease-causing agents over time and space.
· Provides an understanding of how people are exposed to harmful materials and describes what can be done to minimize or prevent such exposure.
The civilized existence of man is made possible by keeping him physically healthy through the application of medical knowledge. Although this is an important aspect of life, surprisingly little serious attention appears to have been given to it by the very persons who should have realized its important role in the study of the effects of various elements and metals on the human body.
Every day we eat, drink and breathe minerals and trace elements, never giving a thought to what moves from the environment and into our bodies. For most of us this interaction with natural materials is harmless, perhaps even beneficial, supplying us with essential nutrients. However, for some, the interaction with minerals and trace elements can have devastating, even fatal effects. These interactions are the realm of medical geology, a fast-growing field that not only involves geoscientists but also medical, public health, veterinary, agricultural, environmental and biological scientists. Medical geology is the study of the effects of geologic materials and processes on human, animal and plant health, with both good and possibly hazardous results.
The relationship between the Earth's surface that we humans inhabit and our health is under debate. The fact that a continuum and indelible link exists is not in doubt. We have obtained food, water, and shelter since Homo arrived, but in the twentieth century we have learned that disease as well as health may by derived from our environment.
The geochemical distribution and biochemical availability of the elements that are required for human existence are not uniformly distributed over the Earth's surface. For example, low concentrations of iodine (I) characterize the soils and rocks at high elevations and in limestone terrains. This is a natural global phenomenon. Medical acumen and geostatistical and epidemiological investigations have identified iodine as an essential nutrient. The thick necks that were depicted in ancient Chinese scrolls, and the cretinism found in mountainous regions, are now recognized as symptoms of the endemic disease goitre. Jharkhand and other Eastern states in India are Iodine deficiency zone. Reduction, but unfortunately not eradication, of this preventable malady is now possible through the use of iodine-enriched table salt and oils.
Fluorine (F), another element that is a constituent of some minerals, is now added to drinking water to minimize the development of dental caries, especially in children. Apart from the beneficial effects of maintaining a healthy oral cavity to aid mastication and minimize pain, it is probable that ingestion of fluorine in small amounts (parts per million) over a lifetime will stave off osteoporosis, or at least serve to preserve the mineral materials in the skeleton in old age. It was the recognition of a connection between high natural fluorine concentrations (100 ppm) in the drinking waters of certain localities in Oklahoma and India and overabundant calcium phosphate mineral deposition in the skeleton that most clearly illustrates the essential and continuing basic interactions between geology, geochemistry, medicine, and biochemistry. The fluorine effect, fully researched, led to applications aimed at reduction, if not prevention, of disease.
Radon is a naturally occurring colourless, odourless gas that is emitted from rocks containing minerals rich in the transuranic elements. The occupational health effects, in particular lung cancer, suffered by some European coal-miners who mine such rocks were ascribed to radiation, but may equally well have been induced by smoking. Granites that underlie portions of the north-east of the United States (New England) are known to contain minerals that emit radon. Recent epidemiological studies that measured environmental exposure (the average was less than 4 picocuries for the region) were not able to demonstrate an association between the incidence of lung cancer and sites where radon concentrations (possible doses) were elevated.
In its broadest sense, medical geology studies exposure to or deficiency of trace elements and minerals; inhalation of ambient and anthropogenic mineral dusts and volcanic emissions; transportation, modification and concentration of organic compounds; and exposure to radionuclides, microbes and pathogens.
Hippocrates and other Hellenic writers recognized that environmental factors affected geographical distributions of human diseases 2,400 years ago. And in 300 B.C., Aristotle noted lead poisoning in miners. Rocks and minerals have also been used for thousands of years to treat various maladies such as the plague, smallpox and fevers.
The geological profession has made considerable progress in studies on the distribution of elements, even in traces, in rock materials to understand their manner of evolution. A geochemist who takes to such studies rarely gives a thought as to which of the elements he has been examining are beneficial or harmful to the human race although the civilized existence of man requires a number of elements and metals. The soil which covers the underlying rock, in the process of weathering, concentrates some of these elements and even transfers some to plants growth on such soil, while groundwater which filters through the soil profile dissolves certain other elements. Civilized man, in order to coax more from the soil, adds fertilizers and uses pesticides for destroying pests which affect crop growth. Also with the good intention of keeping the human body in good conditions, he introduces certain elements in the form of drugs under medical advice. The geological factors which control the distribution and dissemination of these elements, as also their presumed therapeutical effects, is a factor of great importance to which geologists must direct their attention.
The types of rocks that form geologic units in the Earth’s crust supply most of the raw materials from which soils are formed and from which water derives it inorganic constituents. The compositions of what we eat and drink thus depend in part upon the compositions of the source rocks. The contents of individual trace elements vary widely with rock type. Chromium, titanium, nickel, and cobalt are conspicuously concentrated in low-silica igneous rocks that are quantitatively unimportant. Arsenic, iodine, molybdenum, and selenium are conspicuously concentrated in shale and clay. Metallic elements present in source rocks in small amounts-the so called minor elements or trace elements- have been shown to have important effects on human and animal health, resulting from their excess or deficiencies in soils, waters, and plants.
Rocks like Igneous, Sedimentary, and Metamorphics contribute trace elements to the water bodies like fluoride, Arsenic, lead, copper, mercury, zinc, etc. Jharkhand state in India provides an ideal opportunity for the study of the effect of geology on human health. The vast majority of the people of Jharkhand still live in rural areas within areas termed geochemical provinces. Very broadly, one could say that a geochemical province has characteristic chemical composition in soil, water stream sediments and rocks, enabling their delineation from others. The chemical composition is presumed to be have an impact on the health of the inhabitants of the particular geochemical province, particularly because of the fact that their food and water are obtained mostly from the terrain itself. This leads to the concept of "diseases of geochemical origin". Among these are dental fluorosis, iodine deficiency disorders (IDDs) and Arsenic toxicity based diseases.
Author has worked on distribution of trace elements in Permian coals of North Karanpura Coalfield of Jharkhand State of India and its environmental impact. It was found that concentration of arsenic in coal samples range from <0.01 to 0.49ppm with an arithmetic mean of 0.15ppm. (Priyadarshi, 2004). Concentration of arsenic is low compared to most world coals. Average ash% is very high (up to 32.51%). Average concentration of arsenic in the sediments of mine water was 1.4 ppm. Though the concentration of arsenic is low in the surface water ( 0.001-0.002 ppm) it may still affect the local habitants especially during summer season when the consumption of water increases many folds. Main source of arsenic in the water bodies is from the coals of the researched area. Elements like lead, barium, strontium, boron, etc. were also present in sufficient amount in the coals.
The low arsenic concentrations of the coal studied could be related to the geological characteristics of the source area in the basin and to a resulting low degree of arsenic mineralization (realgar or orpiment) of the synsedimentary solutions, which resulted in a paucity of arsenic in the system.
A detailed study has been presented on groundwater metal contents of Sahebgunj district in the state of Jharkhand, India with special reference to arsenic. Both tubewell and well waters have been studied separately with greater emphasis on tubewell waters. Groundwaters of all the nine blocks of Sahebgunj district have been surveyed for iron, manganese, calcium, magnesium, copper and zinc in addition to arsenic. Groundwaters of three blocks of Sahebgunj, namely, Sahebgunj, Rajmahal and Udhawa have been found to be alarmingly contaminated with arsenic present at or above 10 ppb.
Bakhari village, situated about 20 km from the Ranchi district headquarters in Jharkhand state , has a population of nearly 700, comprising mostly tribal and members of socially underprivileged groups. Two-thirds of the villagers have reportedly developed physical deformities as all the sources of drinking water in Bakhari have excess fluoride content.
It is to be expected that in areas characterized by metal-bearing formations, metals will also occur at elevated levels in the water and bottom sediments of the particular area. There is evidence that the high mercury content in rocks encountered in the catchment of La Grande River, Canada, may be responsible for high mercury levels in organisms (Boyle and Jonasson,1973). It was found that the Aphebian Shale in central and northern Quebec- near the headwaters of the La Grande- contained mercury levels averaging 0.5 ppm , which these authors regard as being high.
A study conducted by Colbourne et.al. (1975) confirmed that the stream sediment patterns for arsenic and copper in the Dartmoor area of South-West England may be correlated with significant enrichment of these elements in soils derived from rocks within the metamorphic aureole around the Dartmoor granitic intrusion. Previously it had been concluded that the source of arsenic within the metamorphosed country rocks was the result of hydrothermal activity during phases of granitic intrusion. Similarly, geothermal sources in North Island are a natural source for mercury enrichment.
All living tissues are composed mainly of eleven elements, but to remain viable, minute amounts of a few elements of the transition series also must be present. These act as mediators of the biocatalysts, the enzymes. The trace elements that have been most extensively studied are : Fe, Cu, Mn, Mg, Mo, and Zn. The body as it ages concentrates a large number of other elements; many of these, when present in excess, have been reported as being responsible for the introduction of cancer. Experiments reveal that nickel, cadmium, and some chromium compounds are true metal carcinogens. Arsenic has been strongly indicted as a primary human carcinogen. Asbestos may prove to be a carrier for the carcinogenic metals, nickel and chromium. In the 1980s, earth scientists helped medical scientists to recognize that there was more than one type of material called asbestos, and that the different asbestos materials are not equally carcinogenic. Chrysotile asbestos, for example, is commonly regarded as being less carcinogenic than amphibole asbestos. The last several years have seen renewed public attention on the potential health effects of asbesti form minerals that occur naturally as trace constituents in rocks or mineral deposits. For example, in 1999 the Seattle Post-Intelligencer brought nationwide media and scientific attention to asbestos-related health problems in residents of Libby, Mont. Many residents have diseases that have since been attributed to their exposure to amphibole asbestos minerals. The minerals were naturally inter grown with the vermiculite mined and processed at Libby.
Mercury is regarded as the most toxic metal, followed by cadmium, lead and others although there is no rigid order of toxicity. Contamination of the aqueous environment by cadmium appears to be less widespread than by mercury but has nonetheless hazardous effects on humans. During 1947 an unusual and painful disease of a “rheumatic nature” was recorded in the case of 44 patients from villages (e.g., Fuchu) on the banks of the Jintsu River, Toyama Prefecture, Japan. During subsequent years, it became known as the “itai-itai” disease (meaning “ouch-ouch”) in accordance with the patients shrieks resulting from painful skeletal deformities. However the cause of this disease was completely unknown until 1961, when sufficient evidence led to the postulation that cadmium played a role in its development.
Exposure to toxic levels of trace elements is one of the widespread forms of environmental health problems. Millions of people worldwide suffer health problems because they have been exposed to arsenic, lead, fluorine, mercury, uranium, etc. The devastation caused by excess arsenic in drinking water in Bangladesh, West Bengal India and elsewhere has been headline news. An estimated 25 to 75 million people are at risk of arsenosis in that region.
In Guizhou Province, China, the cool, damp autumn weather forces villagers to bring their harvests of chili peppers and corn indoors to dry. They hang the peppers over unvented stoves that, until the middle of the last century, had been fueled by wood. Due to the destruction of the forests, wood is now scarce so the villagers have turned to the plentiful outcrops of coal for heating, cooking and drying their harvests. But mineralizing solutions in this area have deposited enormous concentrations of arsenic - up to 35,000 parts per million - and other trace elements in these coals.
The chili peppers dried over these arsenic-rich coals are a key component of the villagers' diet and, unfortunately, their principal source of arsenic. Thousands of villagers are now suffering from arsenic poisoning and exhibit typical symptoms, including hyperpigmentation (flushed appearance, freckles), hyperkeratosis (scaly lesions on the skin, generally concentrated on the hands and feet), Bowen's disease (dark, horny, pre-cancerous lesions of the skin), and squamous cell carcinoma.
Most trace elements in drinking water are of concern from a public health point of view because of potential for excess above recommended limits. However, some trace elements are essential to health and so are required to be present at certain concentrations in drinking water or food. Iodine is one such essential element. Deficiency in dietary iodine can lead to a number of iodine-deficiency disorders (IDDs) in humans. No regulations or recommendations are placed on concentrations of iodine in drinking water because such standards are imposed to regulate upper rather than lower limits.
As iodine is an essential element for humans, there is considerable interest in its environmental geochemistry. It is unique amongst the elements in that most iodine in the terrestrial environment does not derive from normal weathering of crustal rocks but derives through volatilisation from the oceans, which represent the major reservoir of iodine on the Earth. As a result of this major source of environmental iodine, soils in coastal regions are strongly enriched in iodine, while those far removed from marine influence generally have low iodine contents.
Iodine concentrations in groundwaters (and surface waters) largely lie in the range 0.01–70 µg/l, depending on geographical location and local geology and soils. Higher concentrations can be found in saline waters such as coastal and arid or semi-arid areas. The principal sources of iodine in groundwater are aquifers and soils and the atmosphere. Iodine is found in low concentrations in most rocks because it is incompatible with most rock-forming (silicate) minerals. It may be present in higher concentrations in sulphide minerals, organic matter and iron oxides. Hence sulphide-, organic- and iron- rich rocks and soils tend to have the highest concentrations. Mineral veins (rich in sulphide minerals) and hydrothermal solutions are also relatively concentrated. Of the sedimentary rocks, muds and shales typically have the highest concentrations. Weathered rocks often have higher iodine concentrations than their pristine equivalents, presumably due to interaction with groundwater.
Uranium is present in the environment in low concentrations in all parts of the world, the most abundant deposits being in sedimentary rocks. The main areas of the world with rich uranium deposits are the Colorado plateau in Wyoming in the United States, Blind River and Beaver Lodge districts in Canada, the Erz Mountains in central Europe, the Ural Mountains in Russia, the Rand Mountains in South Africa, the French Alps, Radium Hill in Australia, Jadugoda in India and the Pirinean Mountain range in Spain. Open pit mining has been the preferred way of uranium production, but some deposits are too deep for this type of mining because it necessitates deep underground mining. The range of uranium content of the most ores is between 0.1-1.0% of U3O8. However, much higher grades are frequently found, presenting higher radiation hazards to miners from beta radiation from the ore and inhalation of uranium dust suspended in the air of the mining environment.
Normal functioning of the kidney, brain, liver, heart, and numerous other systems can be affected by uranium exposure, because in addition to being weakly radioactive, uranium is a toxic metal.
As we contemplate an increase in world population and an ageing population, it becomes apparent that evaluating long-term exposure to natural materials in our environment makes cooperation and coordinated study of geology and medicine essential. The intertwining of these areas of knowledge should enable us to continue to improve health and combat disease, and contribute to better living conditions for all people.
Medical geology, a long-recognized but perhaps underutilized discipline, presents the geoscience community with tremendous opportunities for collaborative work with the biomedical and ecological research communities. Such collaborations have great potential to help understand, mitigate and possibly eradicate environmental health problems that have plagued humans for thousands of years.
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Colbourne, P., Alloway, B.J., Thornton, I., 1975. Arsenic and heavy metals in soils associated with regional geochemical anaomalies in southwest England. Sci. Total Environ. 4, 359-363.
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